january/february 2017 · pdf fileviewpoint rainstorm in the cloud by alix paultre, editorial...

January/February 2017

Special Report: Consumer Electronics (pg 27)

VIEWpoint

Rainstorm in the CloudBy Alix Paultre, Editorial Director, Power Systems Design

POWERline

Ambiq Micro’s Apollo 2 can double battery life in wearables

NOTABLEandNewsworthy

Thermoelectric paint harvests energy from almost any heat

MARKETwatch

Keeping up with consumerBy Kevin Parmenter, PSD Contributor

DESIGNtips

Using supercapacitors in energy harvesting

By Pierre Mars, CAP-XX

COVER STORY

Advanced distributed power

By Mark Adams, CUI, and Mark Patrick, Mouser Electronics

TECHNICAL FEATURES

Test & Measurement

Measuring the power of complex RF waveformsBy Giovanni D’Amore, Keysight Technologies

Automotive

Busbar choices for EV power distributionBy Dominik Pawlik, Rogers Power Electronics Solutions

Marine

Powering marine

By Patrick Le Fevre, Powerbox

SPECIAL REPORT:CONSUMER ELECTRONICS

Smart dimming technologies

By David Gamperl, ams

Step-by-step

By Andrea Colognese, Rohm Semiconductor

Innovative topology

for piezo drivers

By Jim Mutzabaugh, Apex Microtechnology

Empowering wireless

charger design

By Eko Lisuwandi, Linear Technology

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ROUNDupCES

Consumer Electronics Las VegasBy Alix Paultre, Editorial Director, Power Systems Desig

PAULTREonPower

The design explosionBy Alix Paultre, Editorial Director, Power Systems Design

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Highlighted Products News, Industry News and

more web-only content, to:

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COVER STORY

Advanced distributed Power (pg 10)

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POWER SYSTEMS DESIGN

This year’s CES, the 50th, was a geek orgy of gadgets and their related services and infrastructures, each vying for attention in the hopes that it will be the “Next Big Thing”. The reality is that there probably won’t be any one new big shiny thing going forward, the big thing is that there are a lot of powerful little things now working together to create devices for the IoT and infrastructure technologies for the Cloud that supports it.

This year’s CES underscored that concept in spades, with a plethora of products and services. Some of them were quite innovative, and some just seemed to be there because the functionality behind them can now be created.

A popular example that attracted a lot of attention at CES was a laundry-folding machine that supposedly would reduce your cleaning workload by folding your clothes for you. The problem is that it can’t just take a mass of clothes, separate them, and fold them, you have to separate the clothes and then hand each one in the machine for it to properly access them. A large step in the right direction, but with too much hand-holding to make it a truly functional solution.

Another good example was an intelligent hair brush that not only allowed you to align your hair and clean out any debris the way a normal brush would do, but also used an array of sophisticated sensors to tell you why you were having a bad hair day. Frankly I could skip the analysis and go straight (pardon the pun) to fixing the bad hair, but the brush can only tell you that there is a problem, it cannot address your bad hair itself.

The personal products space is now jammed with gadgets and wearables that will tell you how wet you are, how dry you are, how fast you are moving certain parts of your body, and whether or not you are moving those body parts in the proper way to get a good workout. Some of the personal devices will even yell at you to motivate you into proper behavior and motions. You can now store and analyze all sorts of personal data, from how effectively you are hydrating yourself to how long you are brushing your teeth and the areas in the mouth you missed.

A lot of these devices will turn out to be fads, flashes in the pan that promised great things only to disappoint, or services to address demands that did not materialize. But it is extremely important that we have these odd and novel devices and services appear on the scene, even if only to disappear a short while afterwards leaving us all bemused, as the industry is always richer for it.

Best Regards,

Alix PaultreEditorial Director, Power Systems [email protected]

Rainstorm in

the CloudPower Systems Corporation 146 Charles Street Annapolis, MD 21401 USA Tel: +410.295.0177Fax: +510.217.3608 www.powersystemsdesign.com Editorial Director Alix Paultre, Editorial Director,Power Systems Design [email protected]

Contributing Editors Liu Hong, Editor-in-Chief, Power Systems Design [email protected] Kevin Parmenter, PSD Contributer

Publishing Director Jim Graham [email protected]

Publisher Julia [email protected]

Production Manager Chris [email protected]

Circulation Management Sarah [email protected]

Sales Team Marcus Plantenberg, [email protected]

Registration of copyright: January 2004ISSN number: 1613-6365

Power Systems Corporation and Power Systems Design Magazine assume and hereby disclaim any liability to any person for any loss or damage by errors or ommissions in the material contained herein regardless of whether such errors result from negligence, accident or any other cause whatsoever.

Free Magazine Subscriptions, go to: www.powersystemsdesign.com

Volume 14, Issue 1

Service roboticsMaking everyday life easier

Service robots offer welcome assistance to millions of people worldwide – from performing household chores to helping sick, elderly or disabled people. But with their assistance and the resulting close interaction with humans also come unique challenges from a design perspective. While being durable and reliable service robots must also be able to sense human beings and their needs – capabilities made possible by Infineon’s specialized solutions.

Benefits for you: › Strong – more power with OptiMOS™ and StrongIRFET™

› Light and compact designs – lowest RDS(on) of Infineon power semiconductors e.g. OptiMOS™, StrongIRFET™ and CoolMOS™ allowing highest power density and reduction of cooling elements

› Quiet – smooth and quiet motor control by powerful microcontrollers and sensors

› System cost reduction – by excellent price/performance ratio of semiconductor devices

› Easy control method – enabled by microcontrollers (XMC™) & quick software realization due to tailor-made graphical user interface (GUI) DAVE™

› Infineon is a one-stop semiconductor shop for all your service robotics design needs

So delve into our portfolio to find the solutions and components that will take your service robotics designs to the next level.

For more information please visitwww.infineon.com/service-robotics

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POWER SYSTEMS DESIGN 2012OCTOBER

Ambiq Micro, a leader in ultra-low power solutions, released the Apollo 2 Wearables

and IoT Platform. The Platform offers breakthrough power consumption of under 10µA/MHz, which allows for double the battery life in wearable devices. Apollo 2's performance will lead to longer battery life, enhanced intelligence and improved functionality in wearables and IoT consumer electronics (CE) products. Ambiq Micro's Apollo 2 Platform provides dramatic reductions in energy consumption through its patented Subthreshold Power Optimized Technology (SPOT) technology.

Today’s consumers demand sig-nificantly extended battery life, sleeker and more fashionable form factors, as well as myriad power-ful features from their wearable devices. These benefits, however, are only possible with greatly-re-duced energy consumption, which is achieved using devices such as Ambiq Micro’s Apollo, powered by SPOT.

"The incredible pace of Moore's Law disrupted computing every year or two and took us from room-sized supercomputers to billions of pocket-sized mobile phones," said Scott Hanson, founder and CTO, Ambiq Micro.

Ambiq Micro's Apollo 2 can double battery life in wearables

"Ambiq Micro's SPOT tech-nology will bring a similar pace of innovation to the IoT. As the foundation of our Apollo MCU, SPOT allows us to drive energy consumption below what we previously imagined was possible. With Apollo 2, we extend the SPOT technology to achieve new ef-ficiencies for the next wave of IoT and connected devices."

Wearables and IoT devices need a longer battery life or smaller bat-teries to create slimmer and more fashionable form factors. To meet customer demands, devices must be always on, always connected and always aware. In order to provide that functionality without compromising battery life, devices will require lower power consump-tion standards.

Ambiq Micro's Apollo 2 provides wearables and IoT device original equipment manufacturers (OEMs) a platform with a 5x reduction in power consumption, which leads to double the battery life of com-petitors. The Apollo Platform con-sumes an industry-leading 34µA/MHz when executing instructions from flash memory and features sleep-mode currents as low as 140nA.

"The market for wearables and

IoT devices is growing rapidly, especially with younger genera-tions accustomed to always-on and always-aware aesthetically designed devices enhancing their daily lives," said James Lee, Presi-dent, Foxlink "This growth and stringent expectation mean chips powering our devices need to be faster and more efficient than ever. With Ambiq Micro's Apollo 2, we can offer some of the most feature-rich devices to consumers without sacrificing precious battery life or introducing unnecessary form fac-tor constraints."

Ambiq Micro offers a wearables and IoT platform with ultra-low power consumption. A variety of major brands and OEMs are cur-rently using Ambiq Micro's tech-nology to build the most challeng-ing low-power devices.

Ambiq Micro www.ambiqmicro.com

Thermoelectric paint harvests energy from almost any heat

A new study, led by Professor Jae Sung Son of Materials Science and Engineering

at UNIST has succeeded in developing a new technique that can be used to turn industrial waste heat into electricity for vehicles and other applications.

In their study, the team presented a new type of high-performance thermoelectric (TE) materials that possess liquid-like properties. These newly developed materials are both shape-engineerable and geometrically compatible in that they can be directly brush-painted on almost any surface.

As well as waste heat recovery system for ships. In addition, the thermoelectric generator modules used in these devices are configured as rectangular parallelepipeds.

The output power of thermoelectric generators depends on device engineering minimizing heat loss, as well as inherent material properties. According to the research team, the currently existing liquid-like TE materials have been largely neglected due to the limited flat or angular shape of devices.

However, considering that the

surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, the research team presented the shape-engineerable thermoelectric painting technique where they directly brush TE paints onto the surface of heat sources to produce electricity.

Using this technique, one can now easily achieve electricity via the application of TE paints on the exterior surfaces of buildings, roofs, and cars. Scientists hope that their findings, described in the prestigious journal Nature Communications this week, will pave the way to designing materials and devices that can be easily transferred to other applications.

To show the feasibility of the currently proposed technology,

they also fabricated TE generators through painting TE paints on flat, curved and large-sized hemispherical substrates, demonstrating that it is the most effective means of heat energy collection from any heat sources with exceedingly high output power density of 4.0 mW cm−2, which is the best value among the reported printed TE generators.

“By developing integral thermoelectric modules through painting process, we have overcome limitations of flat thermoelectric modules and are able to collect heat energy more efficiently.” said Professor Son. “Our thermoelectric material can be applied any heat source regardless of its shape, type and size.” said Professor Son.

UNIST www.unist.ac.kr

NOTABLEandNewsworthy

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MARKETwatch


By: Kevin Parmenter, Power Systems Design Contributor

The consumer electronics market is growing, yet it’s always in a state

of flux. In this huge and competitive market you must have the latest features and functions and the best, easy-to-use interface or your products will be yesterday’s news and they won’t sell. The typical pace of the consumer market is 3-6 months, so once the newer models are released you better have an offering with the latest technologies on them. The stakes are also high since safety and quality missteps are extremely costly. Imagine airlines telling your customers they can’t bring certain models of your products on planes on penalty of being fined and removed from the aircraft. From power electronics industry perspective, the safety standard we’ve all been working with is IEC60950. But that is now being replaced with IEC62368. This new risk-based standard covers audio/video, information and communication technology equipment. Since this standard proves to be the one that covers both consumer electronics and

Keeping up with consumer

industrial power supplies, it’s incumbent on us to learn all about it. Hopefully by meeting the new standard, organizations can cut down on recalls, especially battery and power electronics related incidents. Consumer electronics are setting the bar for ease-of-use and GUIs and smart manufacturers are mindful of this. An interesting side effect from improved consumer electronic interfaces is that consumers have come to expect user-friendly interfaces in the work environment. For instance, a nurse or lab tech now expects the same intuitive, reliable, high-resolution graphics touch screen interface on their $200 phone to be as good or better on the $200,000 clinical chemistry analyzer that they use at work. In my view, consumer electronics will continue to expand rapidly due to the possibilities provided with connectivity and the falling price of computing power. For example, a garage door opener was not thought of as a consumer electronics product until recently, but now an interface for your garage

door opener can be connected to your home Wi-Fi and your cell phone app will allow you to open and close the door and alert you to when it goes up and down – plus you can read the temperature in your garage. Also newly considered a consumer electronics products are light bulbs and thermostats, thanks to smart lighting Wi-Fi connected products. The largest electronics show on earth, the Consumer Electronics Show, or CES, will have already happened when you read this, but the themes have already been announced: connectivity, 5G specifically; drones; virtual reality; self-driving vehicles; GPU’s (graphics processors); immersive entertainment, including video and audio products; consumer convenience products; wearables and of course IoT and IoE. Semiconductor companies also will be in attendance to promote reference designs for key consumer vertical markets. As these applications grow and improve, they will need to be powered and/or charged.

By: Pierre Mars, CAP-XX

The environment has abundant energy, so energy harvesters are an ideal power source

for Internet of Things (IoT) ap-plications, eliminating the need to replace and dispose of batteries. However, small energy harvesters often cannot provide the peak pow-er required to collect and transmit data. Let’s take a look at how to use a supercapacitor charged from an energy harvester to provide the peak power required using a small solar cell as a case study.

The typical power architecture has an energy harvester supplying a supercapacitor charging circuit with the supercapacitor directly supplying the load. The high C and low ESR of the supercapacitor maintains a sufficiently stable volt-age for the load to function during its peak power bursts.

Characterize the energy harvesterExperimentally verify the power available from your energy harvest-er in your expected conditions. For example, a well-lit office is ~500lux but solar cell power is typically quoted at 50,000 lux (summer day) or 100,000 lux (1KW/m2). Connect a potentiometer and current sense resistor across the solar cell array in the light level

Using supercapacitors in energy harvesting

you require and vary the resistance from open circuit through to short circuit, measuring current and voltage at each step deriving a V-I curve and the peak power avail-able. Consider the open circuit voltage and voltage at the peak power point when selecting your solar cell array – determined by the number of cells in series, ~0.65V/cell, which determines the possible charging ICs (constrained by input voltage range), and whether to use a single-cell supercapacitor (2.75V max) or dual-cell supercapacitor (5.5V max), and how the super-capacitor is coupled to the IoT application. Figure 1 shows the V-I curve for the solar cells used for this case study at ~500 lux, peak power = 1.4mW at 2.6V.

The energy harvester supplies low

average power to charge the su-percapacitor, which then supplies periodic or sporadic peak power to collect and transmit data. The power available from the energy harvester sets the power budget:

IoT power x duty cycle = EH average power.

Set how often the IoT application reports to meet the power budget available from your energy harvester.

Supercapacitor PropertiesSupercapacitors are ideal power buffers between an energy har-vester and a load demanding more power than the energy harvester can deliver, due to:• Low ESR to enable high power

delivery

Figure 1: V-I curve for solar cell array in typical light conditions

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input current. Figure 3 shows our circuit.

However, we have found this IC would not start charging a super-capacitor from 0V and did not behave gracefully into a short circuit. It recognized a discharged supercapacitor as a damaged battery. To overcome this, we bypassed the BQ25504 with M2 to charge the supercapacitor directly until 1.8V. Initially the gates of M1 and M2 are high with the source of M2 = 0V (discharged super-capacitor) and the source of M1 high (open circuit voltage of solar cell, turning M2 ON and M1 OFF. When the supercapacitor reaches 1.8V the output of U1 turns low, turning M2 OFF and M1 ON and the supercapacitor is charged by the BQ25504.Figure 4 compares the two charg-ing circuits. The BQ25504 circuit charged in 2.4hrs compared to 3.5hrs for the direct charge circuit. The direct charge circuit has the advantages of simplicity and low cost but the disadvantages of a 1.1

hour (45%) longer charge time, and the supercapacitor won’t charge if light levels fall so that the solar cell voltage < superca-pacitor voltage + VF of D1.

The boost convertor circuit has the advantages of maximizing solar cell output power and still charging the supercapacitor even if light levels fall so that the solar cell voltage falls to ~130mV, but only if light levels during initial charge are sufficient to charge the supercapacitor to 1.8V through M2.

Sizing the supercapacitorConsider the supercapacitor’s ESR when sizing it. Vi = superca-pacitor initial voltage. If the load draws a constant current IL for duration T during peak power events then final voltage,

Vf = Vi - IL.ESR – IL.T/C

For a constant power require-ment, P, lasting duration T, then Energy = PT. As the supercapaci-

tor voltage drops, the load cur-rent increases to keep P = VL.IL constant. Let Vint_f = final inter-nal supercapacitor voltage, not including the voltage drop due to ESR, then Vint_f = √(Vi2 – 2PT/C) ……….(1)Vf = Vint_f – IL.ESR……….(2)P = Vf.IL……….(3)

Where Vf is the final load voltage including the voltage drop across ESR. Combining equations (2) and (3) we have:P = (Vint_f – IL.ESR).IL orIL

2.ESR –Vint_f + P = 0 ……….(4)

Solving (4), ……….(5)Vf is given by equation (2) substi-tuting for Vint_f in equations (2),

(3) and (5) from equation (1) and for the value of IL from equation (5). Select C and ESR such that Vf is > minimum voltage required to run the application. Allow head-room for supercapacitor ageing as there will be some C loss and ESR increase over time.

Charging forwardSupercapacitors, with high C and low ESR are an ideal power buffer to enable peak power IoT applications using low power energy harvesters. We have can-vassed principles of supercapaci-tor charging circuits with a solar cell case study and how to size a supercapacitor.

www.cap-xx.com

Figure 4: Comparison of direct charging and charging through a boost converter with MPPT

• High C to support the peak power demand for the dura-tion required

• Low leakage current, impor-tant not to waste the low charge current available

• Simple charging• Single cells up to 2.8V, suit-

able for many applications that can run in the 1.8V – 2.5V range. Dual cells can be used in series for voltages up to 5.5V

• Small thin form-factors for IoT applications, particularly wearables

An example is the CAP-XX HA130 which is 20mm x 18mm x 1.7mm, 800mF, 60mΩ ESR, 2.75V, typi-cal leakage current 1µA. Organic electrolyte supercapacitors have an order of magnitude lower leakage current than aqueous electrolyte supercapacitors, but require over 48hrs on volt-age to decay to final levels of leakage current.

Supercapacitor ChargingSupercapacitors are much simpler to charge than batteries, only requiring charge current and over-voltage protection rather than a constant-current constant-voltage charge regime. Supercapacitors

charge from 0V and due to their low ESR and high C will look like a short circuit to the charging circuit.

Supercapacitor charging circuits must:• Start charging from 0V• Behave gracefully into a short

circuit• Provide over-voltage protec-

tion• Prevent the supercapacitor

from discharging back into the source

• Be designed for maximum efficiency

Most energy harvesters have high input impedance, so will charge directly into a supercapacitor at 0V, supplying short circuit current.If a solar cell array is configured so that:

Target Supercapacitor charge voltage < Solar cell open circuit voltage in your application’s light level < max supercapacitor volt-age

then the simplest charging cir-cuit is that of Figure 2, since the supercapacitor cannot go over voltage. D1 prevents the superca-pacitor discharging back into the solar cell when light fades. The BAT54 is chosen for its low for-ward voltage at low currents and low reverse leakage current.

Alternate pathsAn alternative approach, which maximizes efficiency, is to use a boost converter with maximum power point tracking (MPPT). The IC varies the input current drawn to maintain the solar cell near its peak power point and still charges the supercapacitor when light level falls so that solar cell voltage < supercapacitor charge voltage. We chose the BQ25504 from TI since it only requires 15µW and 330mV at the input to run, and is 80% efficient with only 10µA

Figure 3: Supercapacitor charged by solar cell with MPPT Boost Converter

Figure 2: Simplest Supercapacitor Solar Cell Direct Charging Circuit

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Advanced distributed power

By: Mark Adams, CUI, and Mark Patrick, Mouser Electronics

Making true multi-sourcing of digital DC/DC converters a reality

DC-DC converter mod-ules have been around a long time and can be found in most power

conversion stages of virtually every application today. As their use evolved to changing application requirements so did the design approach used to construct them.

One of these trends meant that in order to preserve conversion efficiency, in a distributed power architecture, it was necessary to undertake the last stage of volt-age conversion as close as pos-sible to the load. Named point of load (POL) converters, and typi-cally powering a microprocessor or a programmable logic device such as an FPGA, this approach boosts overall power conversion efficiency in addition to improv-ing output voltage stability re-sulting from stray impedances in system wiring or long PCB tracks.

As the use of a distributed power architecture grew in popularity, so did the need for provisioning different voltage rails, both regu-lated and unregulated, and the concept of the intermediate bus architecture (IBA) was formed (see Figure 1).

Finding the right solutionAs DC-DC converter modules be-

came a fundamental component in many designs, customers became more concerned about supply chain reliability and the need to second-source equivalent devices. Power industry trade associations led the drive to create standards to tackle these issues.

For the most part, the specifica-tions developed addressed the important issues at that time, that of ensuring devices had a standard mechanical footprint and the core electrical characteristics of output power, input voltage range, etc. Often the standards applied to a particular category of converter such as regulated or non-regulat-ed. What they did not address was what happened inside the convert-er modules themselves, such as the conversion topology, making

the process of swapping out one DC-DC converter for another one from another manufacturer not as straightforward as it should have been.

These standards satisfied the in-dustry's need for second-sourcing converters until two other related trends combined to shake up the DC-DC power conversion market-place. The first was the launch of digital signal processing devices for use in power conversion appli-cations that spawned the creation of digital DC-DC converters. Hav-ing the ability to influence precisely the control loop of the conversion process meant that you could vary output voltage(s) dynamically to suit load conditions. This tech-nology trend was complemented very shortly after by a coalition of

leading semiconductor vendors to establish a standard communica-tions protocol to digitally monitor and control the power conversion process. The industry standard PMBus protocol was formed.

It should be briefly mentioned that an alternative approach to hav-ing to consider second sourcing a module is by designing a discrete DC-DC converter into the applica-tion. While discrete designs do have their merits in low power or extremely cost-sensitive high volume applications, engineering expertise and time to market are becoming increasing factors in the “make vs. buy equation.”

Having the skills to architect an efficient conversion circuit is the reserve of experienced power systems engineers, of which there are very few. Also, given the nature of the development process, it is unlikely that an engineer would opt for this approach for a high current application due to the intricacy of the design and the expertise needed to accomplish the required outcome.

Embracing digitalEmbedded developers have in-creasingly been adopting digital DC-DC converters over the past years. Complex programmable devices like FPGAs now require sophisticated power management functions such as device sequenc-ing and controlling ramp rates in order to operate correctly. Also, the pressures of space-constrained applications have made board

space and the need to reduce the number of external components an absolute priority, for which these digital converters are a perfect fit.

Sharing characteristics such as power switching and output filters in common with analog controlled DC-DC converters, the digital de-vices benefit significantly from the dynamic flexibility to control power delivery to the load in real-time and accommodate changes in load conditions on-the-fly. Communica-tions, monitoring, and control are implemented over the industry-standard PMBus.

Improving the overall power ef-ficiency of the power conversion system is also key. Using digital power modules also simplifies or enables many other aspects of power system design including active current sharing, voltage sequencing, tracking, soft start and stop, and synchronization. In data networking applications, this is particularly important since the power budget required increases

with data throughput. Being able to adjust the converter to still oper-ate efficiently and at a lower clock rate during low data throughput periods is vital.

At low loads the power supplies are relatively inefficient, resulting in excessive energy consumption and waste heat generation, with undesirable technical, financial and environmental consequences. By implementing a digital control loop encompassing both interme-diate bus and POL converters, the intermediate bus voltage can be varied dynamically in response to varying loads. The input voltage to the POL converters can be ad-justed under low-load conditions, increasing conversion efficiency at low loads.

An example of a digital POL DC-DC converter is the NDM2Z-50 from CUI (see Figure 2). This single output converter has an input voltage in the range of 4.5 to 14 VDC and a programmable output voltage ranging from 0.6

Figure 1: Intermediate bus architecture uses multiple PoL converters on the same board (source AMP Group)

Figure 2: Example digital POL DC-DC converter, the NDM2Z-50 from CUI (source CUI)

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COVER STORY


to 3.3 VDC capable of deliver-ing up to 50 A output. Equipped with a host of PMBus-controlled features such as voltage track-ing, synchronization, and phase-spreading together with monitor-ing key operating parameters, this highly efficient and compact converter module is available in either vertical or horizontal formats.

Techniques such as dynamic volt-age scaling (DVS) can be used to save energy. Should the demand for compute resource reduce, then the clock frequency of a processor together with its sup-ply voltage can also be reduced. Typically DVS, an open loop function, can be implemented by using a simple look-up table that matches pre-determined combi-nations of frequency and supply voltage to the processor's com-pute demand.

Another approach, operating as

a closed loop function, is that of adaptive voltage scaling. Slightly more advanced compared to DVS, AVS adapts the voltage delivered to the processor to the minimum required taking account of its clock speed and compute loading.

The benefit to controlling a digital converter’s switching frequency via the PMBus can be

seen in Figure 3. This example, using the NDM2Z-50 mentioned above, highlights the impact that switching frequency has on the operating efficiency across all load conditions. This needs to be considered in context with other parameters such as output voltage and transient response in order to gather a complete viewpoint of the most efficient converter settings required for a given load and voltage output.

A digital converter also makes possible the ability to incorporate a compensation loop, which adjusts the frequency response of the closed control loop, in order to achieve the optimum transient response without affecting stability. Previously, creating the compensation network required a lot of time to perfect, including using trial and error techniques, and something that was prone to changes due to temperature and component aging.

Further developments in semi-conductor process technol-ogy over the past decade have brought to market new process-ing devices that, while provid-ing leaps forward in computing power, have also challenged the demands for power. No longer is regulation tolerance measured in the range of ±10 %. Levels of ±1 % have become the norm, with tolerances of ±0.5% now becoming more common. This next generation of silicon devices is also offering semiconductor vendors better yield rates thanks to digital power. Devices such as FPGAs can be optimized and binned by their ideal core operat-ing voltage.

There is no doubt that adop-tion of standards by the industry has aided the process of second sourcing. This has particularly been the case with mechanical and layout specifications making drop-in replacements possible along with industry consensus regarding popular input and out-put voltages. However, the intro-duction of sophisticated power management ICs, while making the conversion process more ef-ficient and enabling management of the converter possible, has in-creasingly led to a software-driv-en environment. The complexi-ties this software layer brings, in terms of converter configuration parameters and control of the conversion process meant that second sourcing had another set of interoperability challenges to encounter.

Figure 3: Impact of switching frequency on efficiency for a given load condition

Mindful that over the years the standards required for power delivery modules had not kept up with these advances, three industry leaders in digital power, CUI, Ericsson Power Modules and Murata came together to form the Architects of Modern Power (AMP Group) consortium in October 2014. Facilitating a deeply tech-nical collaboration between the parties, the standards the AMP Group has established cover the mechanical, electrical, communi-cations, monitoring and control specifications of a digital power DC-DC converter (see Figure 4). They are defined for both digital POL converters, sub-divided by output current, and for advanced bus converters (ABC). The NDM2Z-50 highlighted above conforms to the megaAMP stan-dard for converters delivering full output current in the range 40 – 50 Amps. Another example of a product conforming to this stan-dard from one of the other found-ing members of the AMP Group, Murata, is the OKDX-T/50-W12-001-C. Not only do the two prod-ucts share identical electrical and mechanical specifications but also the configuration file from one can be used with the other. In the Advanced Bus Converter space, examples of interoperability can be seen in CUI’s NEB-D series and Ericsson’s BMR457 series, which both meet the ABC-ebAMP standard.

Mouser Electronicswww.mouser.comFigure 4: AMP Group standards

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TEST & MEASUREMENT



Measuring the power of complex RF waveforms

By: Giovanni D’Amore, Keysight Technologies

How different approaches influence measurement outcomes using three examples

The ability to make consistent measurements of RF or microwave power

levels is vital to developing effective radio systems and networks. This article explores how different approaches affect the resultant measurements.

The test case compares various approaches to making average power measurements of continuous-wave (CW), multi-tone, 32 QAM (quadrature amplitude modulation), and pulsed signals. A Keysight MXG vector signal generator was used to produce a 6 GHz signal with an output power of -20 dBm.

Power-sensor based measurements used a Keysight U2000A USB power sensor connected to an N9938A FieldFox spectrum analyzer with Option 302. Spectrum-analyzer based measurements used the same FieldFox analyzer, with an integral channel power meter (CPM, Option 310) connected to the signal generator using coaxial cable.

Measuring a CW signal CW signals do not carry information and so the average power and peak power are the same and the signal has no bandwidth. Measurement equipment can use a narrow filter to improve its sensitivity (noise floor).

Figure 1a shows the swept frequency response of a typical spectrum analyzer, around a tone, across a measurement span of 500 kHz. The signal’s peak (and therefore also average) power is -20.08 dBm. The USB power sensor used in Figure 1b gives -20.00 dBm. The CPM option on the FieldFox,

shown in Figure 1c, gives -20.09 dBm.

The three measurements are within 0.1 dB. The power sensor has the highest accuracy, or lowest measurement uncertainty.

Measuring a multi-tone signalIn this example, the power from the signal generator is distributed among five tones at 500 kHz intervals. The peak power of this signal differs from its average power because of the phase relationship between the tones.

If the total power for the tones is -20 dBm (10 µW) then each

has a power of 26.98 dBm (2µW). An average power sensor will measure the average power of all five tones, in this case, -20.13 dBm (see Figure 2a-c). The CPM gives a measurement of 20.2 dBm, so long as the CPM’s measurement span is set to include all five tones (in this case, this demands a span of at least 2.5 MHz).

Power sensors can’t make measurements of single tones or specific measurement spans, because they are not frequency selective. Peak power measurements usually need a sensor that can handle peak powers and a filter wide enough to capture all the tones at once.

Measuring a digitally modulated signalThe digitally modulated signal shown here uses 32 QAM with a symbol rate of 5 Msymbol/s. The symbols are filtered, so the signal bandwidth is approximately 8 MHz (see Figure 3a). The power sensor reports an average power of -20.00 dBm (Figure 3b), and the CPM reports -20.07 dBm (Figure 3c).

A power sensor will report the correct average power of a signal with unknown bandwidth, so long as its power and frequency are within the sensor’s capabilities. To make accurate measurements with the FieldFox you need to set the correct measurement span on its CPM. This can be done by using a standard spectrum analyzer to discover the signal’s bandwidth, and then switching in the CPM once it has the correct span setting.

Measuring pulsed waveformsIn pulsed waveforms, the ratio of the pulse width (how long the pulse is on) to the time between the pulses (its period) is its duty factor (DF). The peak power of such waveforms is the average power divided by the DF, given a repeating pulse-train. Figure 4 shows the measured spectrum and average power of a pulsed waveform with a 20 µs pulse width and a 20% DF.

Figure 4a shows the spectrum

Figure 1: One of the useful attributes of the linear push-pull, analog-bridge topology is that it enables the use of identical compensation for each amplifier.(Figure A top)(Figure B left)(Figure C right)

Figure 2: The Micro-Cap 11 Spice simulation schematic was critical to performing a full evaluation of the design before any actual prototyping of the design. (Figure A top)(Figure B left)(Figure C right)

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rates in its ADC to capture rapid transitions in pulsed and complex modulated waveforms.

A typical peak power sensor has two measurement paths, optimised for measuring either the average or the peak power. In the peak-power measurement path, the sensor has a two-layer detection scheme.

The first detection occurs when the wideband diode rectifies the incoming waveform, while preserving the shape of its envelope. The signal is then amplified and filtered. The filter’s bandwidth is usually

selectable, at up to 30 MHz for the Keysight P-Series and X-Series sensors, and must be greater than the signal under measurement.

The second detection happens after filtering, when the ADC samples the signal (at up to 1 Gsample/s in peak-power meters such as the Keysight 8990). This high sampling rate captures the true shape of the waveform, from which the peak power, pulsewidth, period, rise- and fall time characteristics can be measured or derived.

Making measurements with a

Figure 6: Measuring a pulsed waveform using a peak power sensor connected to a spectrum analyzer (Source: Keysight Technologies)

Figure 5: Block diagram of a peak power sensor/meter (Source: Keysight Tech-nologies)

peak power sensor Peak-power sensors can interface with spectrum analyzers to make field measurements of the time domain profile of a pulsed waveform. Figure 6 shows the measured power envelope of a pulsed waveform as a function of time.

The input waveform is a pulse-modulated 40 GHz signal with a 1 µs pulse width and 10% DF. It was captured using a Keysight N9344C handheld spectrum analyser connected to a U2020 X-Series USB peak and average power sensor.

Using this peak-power sensor, an analyzer can display peak power, average power, and waveform characteristics such as rise and fall times. Markers on the display can be set to show specific timing and power levels in the waveform. The Keysight peak power meters have bandwidths of up to 30 MHz, making it possible to measure waveforms’ rise and fall times down to 13 ns.

This test case has shown that modern power sensors, power meters and spectrum analyzers can make sophisticated measurements on complex signals, but must be deployed with an understanding of their advantages and constraints in order for those measurements to be valid.

www.keysight.com

analyzer display of a typical “sin(x)/x” response as a function of frequency. Sidebands in the frequency domain

continue outside the displayed 1 MHz frequency span. The average power using the power sensor (Figure 4b) is reported

as -27.01 dBm. The CPM (Figure 4c) reports an average power of -26.8 dBm.

For the CPM measurement, the span was set to 3 MHz to capture most of the waveform’s sideband energy (increasing the span beyond 3 MHz did not change the measured power.) The peak power for this waveform with a 20% DF can be calculated by increasing the average level by 6.99 dB (10log(1/DF)). Using a measured average power of -27 dBm, the peak power is calculated as -20 dBm — which is what the signal generator was set to produce.

Detection and filtering in peak power measurements The block diagram for a peak power sensor/meter is like that of an average power sensor (Figure 5), although the peak power sensor/meter has a wider bandwidth and higher sample

Figure 3: The simulation of the closed-loop gain of the circuit shows a gain flatness of ±1.1 dB at 10 MHz, at the selected gain. (Figure A top)(Figure B left)(Figure C right)

Figure 4: The output-voltage and slew-rate measurement shows 360 Vp-p drive to the load with ±100-V supplies. (Figure A left)(Figure B top righ)(Figure C bottom right)

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Busbar choices for EV power distribution

By: Dominik Pawlik, Rogers Power Electronics Solutions

Automotive systems like robust electric motor drives need quality power delivery

Interest in electric vehicles (EVs) and hybrid electric vehicles (HEVs) is growing steadily as battery

technologies improve and the driving range of such vehicles increases. Perhaps as important, EVs/HEVs offer a “green” alternative to traditional vehicles powered by internal-combustion gasoline engines.

EVs and HEVs rely on robust electric motor drives, large-capacity battery pack, power inverters, and efficient distribution of power from charging source to battery and then throughout the vehicle. Busbars, which comprise a system of electrical conductors for collecting and distributing current, provide the means to efficiently distribute power to the vehicles’ various subsystems. A number of different types of busbars are commercially available, so specifying the best match for an EV/HEV application is a matter of understanding the various requirements of an EV/HEV and how different types of power busbars can meet those requirements.

Efficient use of a limited amount of energy is critical to any vehicle design and EVs and HEVs typically work with rechargeable lithium-ion battery backs as their source of energy. Fortunately, the cost of these battery packs has been dropping in recent years, to around a current cost of about $300 USD/kWh. The cost of EV/HEV battery power is expected to continue to drop during the next decade, making EVs and HEVs more affordable and priced more in line with vehicles based on internal-combustion engines.

Acceptance of EVs/HEVs is growing to a point where over 200,000 Nissan Leafs have been sold worldwide. In fact, in some countries, such as Japan, electric vehicle charging stations now outnumber gas stations. Many EVs are now referred to as “plug-in” EVs for their recharging capabilities and are equipped with “fast-charge” charging modes to provide quick energy for shorter driving distances.

Power distribution & driving rangePower storage and driving range

have been chief concerns with EVs/HEVs, with power typically provided by large banks of battery cells combined in sealed packs to achieve the required operating voltage and current to power a vehicle’s electric motor. Of course, induction motors, whether dedicated to each wheel in some novel designs or with power transferred to the front wheel axle through a transmission system, are not the only subsystem in an EV/HEV requiring electric power. All of the basic vehicular functions found in a vehicle powered by an internal combustion engine, including heating, cooling, lights, and warning systems, require electric power in an EV/HEV, and each subsystem when in use can subtract from the total driving range possible with a charged vehicle battery pack.

Fortunately, effective power distribution within an EV/HEV can contribute to improved driving range. A number of battery technologies are employed in new EVs and HEVs, with lithium-ion (Li-ion) technology providing the most

popular solution for the large battery packs that operate the electric drive motor. Traditional lead-acid batteries are still commonly used within EVs and HEVs as auxiliary power sources, for functions such as sensors, cooling fans, and lights. Li-ion battery systems can provide 130 Wh/kg energy capacity and handle thousands of charging cycles with minimum degradation of storage capacity.

For a typical EV or HEV with a driving range of 100 miles or more, this translates into a useful Li-ion battery lifetime of 6 years or more (or the typical warranty period for a new EV/HEV). Several manufacturers are developing variants of lithium-based power cells, including lithium-iron-phosphate batteries and lithium-titanate batteries, attempting to add range to EVs and HEVs, although cost must be within certain limits for competitive automotive markets. Additional vehicular battery technologies include nickel-metal-hydride (NiMH) cells, which are heavier and less efficient than Li-ion batteries, but considerably less in cost, and zinc-air batteries, but Li-ion batteries currently represent the dominant technology in EVs and HEVs.

Connecting cellsCells in a high-power EV/HEV battery pack can be combined in series or parallel to achieve voltage ratings approaching 400

V. Individual cells of about 1.5 to 2.0 V are typically combined using busbars rather than insulated cables. A busbar is essentially an electric conductor and ground plane separated by an insulator. It can be fabricated as a single layer component or with multiple layers, including circuit paths for signals as well as for distributing power.

As with other basic circuit components, a busbar can be characterized by its resistance, capacitance, and inductance, ideally with its electrical contributions distributed as evenly as possible across its length to avoid performance inconsistencies. While the lowest possible resistance and inductance values are to be preferred in a busbar for EV and HEV power distribution, some busbars for that purpose have capacitance added in different ways to increase the charge-carrying capabilities of the power-distribution structure.

Because even low resistance will cause heating effects from large current flow at high enough power levels, it is important to minimize the contact resistance at all connection points along a busbar, including solder joints. To minimize contact resistance, groups of battery cells are often laser welded to a busbar in the process of assembling the large, high-power battery packs for EVs/HEVs. Laser welded connections can also be made as part of an

automated assembly process to minimize manufacturing costs in large-volume production.

Busbars & thermal managementWith the proper materials, a busbar can assist thermal management along with power distribution in an EV/HEV. A busbar’s conductor material and the cross-sectional size of the busbar will determine its current-carrying capacity. Laminated busbars typically consist of copper or aluminum conductors which may or may not be plated with an additional conductive metal, such as silver or gold. Busbars can be fabricated in a variety of shapes, including flat strips, solid rods, and hollow tubes, with flat or hollow forms generally preferred for high-current applications.

Although the AC drive motors used in EVs/HEVs generate very little heat compared to their internal combustion counterparts, the flow of current across any resistive junction in a vehicular power-distribution system can generate heat, including within the battery pack itself. Typically, good electrical conductors such as copper are also good thermal conductors. In a busbar, it is the blend of materials and differences in coefficients of thermal expansion (CTEs) for a busbar’s composite materials that can pose challenges due to ohmic heating and at elevated environmental temperatures.

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Busbars designed for low electrical and thermal resistance can readily serve as part of an EV’s/HEV’s thermal path, from a heat source to a heat sink or coolant reservoir. Busbar materials can also limit process manufacturing temperatures for interconnection methods, such as when using lead-free-solder attachment methods, and expected reliability, particularly if busbar material temperatures are not rated above the temperature limits of a lead-free or reflow solder process.

Along with combining the power cells within an EV/HEV battery pack, laminated busbars offer practical alternatives to multiple-conductor cables for distributing power to the many sensors, subsystems, and other electronic components throughout an EV/HEV. Primary among these different electronic components is the AC drive

motor and inverter system that provides drive power typically to the front axle in an EV/HEV (see Figure 1). The inverter converts DC from the battery pack to the multiple-phase AC power needed by a three-phase induction or permanent-magnet motor.

Power conversion & energy requirementsPower conversion in an EV/HEV usually takes place in several stages, often employing IGBT devices for power conversion. The voltage from the vehicle battery pack is first increased by a DC/DC boost converter to the minimum voltage required by the inverter. This can be a significant increase in DC voltage, from 200 V or less to 600 V or more. Once the voltage is boosted, it is converted to an AC voltage at the proper frequency by means of the inverter to drive the vehicle’s electric motor. Busbars and different connectors

provide practical methods for distributing energy initially from the high-power battery pack to these different power-generating components and on to other components within an EV/HEV electrical system.

Busbars can also serve as a key part of charging process so essential to EVs and HEVs, as a portion of the low-inductance power transmission path that delivers energy from a home or charging station to the Li-ion cells of a vehicle power pack. Mechanically, busbars for EVs/HEVs must be durable, capable of withstanding high levels of vibration, and operate over wide ambient temperature extremes. Electrically, they must provide low-inductance conduction of electrical energy with high isolation from other circuits and potential ground points to avoid arcing.

The energy requirements of an EV/HEV can vary widely, with the largest amounts of electrical energy required by the inverter and electric drive motor. An EV motor has a wide range of power levels, from lower-voltage operation at slow speeds to higher-power use when

accelerating or climbing steep grades. Low-inductance busbars can help achieve low-loss transfer of energy with high energy efficiency from a battery pack, by minimizing energy losses in the power transmission path from an EV’s high-power battery pack to the inverter and electric drive motor.

In contrast to power cables, busbars also make it possible to achieve power distribution with high power density, by mounting active components for power conversion, such as IGBT semiconductors, and passive circuit elements, such as capacitors and EMI filters for noise reduction, on the busbars. In most cases, circuit elements can be incorporated onto a laminated busbar prior to its installation in an EV or HEV, or as part of the busbar’s manufacturing process. Incorporating electrolytic capacitors into busbars for motor drives can improve performance while also conserving circuit volume. For further savings of space within an EV/HEV, hybrid forms of busbars are available with signal paths alongside the power planes for interconnecting sensors and control units to on-board vehicle computers and driver controls.

Performance limitsUnderstanding the performance limits of a laminated busbar can help guide optimum use of

these components for power distribution in EVs and HEVs. As an example, the ROLINX Hybrid from Rogers Corp., Power Electronics Solutions is a laminated busbar that combines power and signal paths in a compact assembly (see Figure 2) suitable for power distribution and signal connections within and from the large rechargeable battery pack in an EV/HEV. In addition to power-handling capabilities that equal or surpass those of shielded cables, the low-inductance busbar provides signal and ground planes for mounting and connection of additional components, including electrolytic capacitors and surface-mount-technology (SMT) components, such as EMI/RFI filters for noise reduction within a vehicle’s power distribution system.

As noted earlier, busbar performance will depend upon the composite materials used

to construct the busbar. The ROLINX Hybrid employs either copper or aluminum conductors in various thicknesses: standard thicknesses from 0.5 to 6.0 mm for copper and from 1.0 to 5.0 mm for aluminum. For any EV/HEV application where heat is a concern, copper offers superior thermal characteristics to aluminum, with thermal conductivity of 401 W/mK for copper compared to 237 W/mK for aluminum, and thermal expansion of 16.5 ppm/K for copper compared to 23.1 ppm/K for aluminum.

Design considerationsIn the design of the conductors for any busbar, the ground return conductor should be at least as large in area as the voltage conductor. This serves to improve the capacitance of the busbar and also provides a sufficiently large ground plane for thermal dissipation and to minimize voltage variations

Figure 2: The ROLINX Hybrid is an example of a commercial laminated busbar that combines signal and power connections to save space in the design of an EV or HEV.

Figure 1: Laminated busbars in EVs/HEVs are essentially for transferring electrical energy from the large high-power battery pack to the inverter for conversion to AC electricity for use by the electric engine.

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due to temperature effects. An adequate busbar ground plane can also help to limit coupling effects from nearby electronic circuits and components in an EV/ HEV.

Insulation/dielectric materials used in the construction of busbars for EVs and HEVs are as important as its conductor materials. Insulation should exhibit stable dielectric constant with temperature so that the resulting capacitance and voltage through a busbar remains stable with temperature. Higher busbar capacitance translates into lower impedance and better rejection of noise, and can be achieved by using thinner dielectric layers between a busbar’s conductive layers.

Insulation is used on both the outside and inside of a sealed busbar construction, with a variety of insulation materials applied, including flexible polyester films (for higher-voltage, lower temperature applications) and polyimide films (for higher-temperature, lower-voltage applications). Inner insulation often includes

some form of filler for increased insulation and rigidity, such as glass fiber or cloth (see Figure 3). When required, busbars can be sealed by means of edge insulation, typically by means of mold or potting.

Specifying busbars for EV/HEVsSpecifying a laminated busbar for an EV/HEV or other application requires an understanding of certain minimum dimensions, including the form factor for a particular EV or HEV requirement and several spacing distances within the busbar, such as clearance and creepage distances. Depending upon the busbar manufacturer and the busbar’s metallization and dielectric materials, the clearance and creepage distances will be a function of voltage capacity. Clearance is the shortest allowable distance in air between two conductors to prevent arcing, while clearance is the shortest distance along the surface of an insulator between two conductors to prevent arcing.

Using a ROLINX busbar as an

Figure 3: The edges of a busbar may or may not be sealed with insulating material depending upon the requirements of an application.

example, the minimum clearance distances for voltages of 750, 1500, and 3000 V are 5.5, 11.0, and 22.0 mm, respectively.

The minimum creepage distances for the same type of busbar for 750, 1500, and 3000 V are slightly less, at 5.2, 10.6, and 21.6 mm, respectively. Such minimum distances must be taken into consideration in the design of any high-voltage busbars and its conductor and connector spacings.

Otherwise, busbar manufacturers can review the minimum requirements for a busbar intended for use within an EV/HEV, or other power distribution application, detailing the tradeoffs between cost and material choices and performance. Of course, for EV/HEV power distribution applications, drive safety is an added concern and busbar materials selection should be performed with the intent of achieving the highest reliability possible, not only for meeting vehicle warranty requirements but for the safety of the driver and passengers.

Rogers Power Electronics Solutionswww.rogerscorp.com

Powering marine

By: Patrick Le Fèvre, Powerbox

What are the challenges?

We are all aware about self-driving cars, and all exciting

projects the automotive industry is engaged in, but very few have heard about unmanned ship and projects to operate large fleets of vessels navigating from dock to dock without operational crews (see Figure 1). In early stages, projects such as Maritime Unmanned Navigation Through Intelligence In Networks (MUNIN) investigated feasibility and test-bed development for future developments. Considering unmanned ships will require extreme reliability from the main

generator to single point-of-load, challenges placed on power designers will be far beyond anything we have known.

State of the art in marine powerFuture generations of power supplies for unmanned ship are still under definition though it is important to understand the specificity of the Marine segment, which is quite unique in terms of environmental and regulations. Due to the nature of the business, the requirements imposed on products and systems deployed in shipping and offshore installations are heavier than what is currently requested for land

industrial and office environment.

In addition, International regulations and standards applying to the Marine Industry are very complex, requiring in depth knowledge of the application and where it will be operated. Power designers must know a lot about marine specific voltage distribution, combining DC and AC networks, safety regulation and many others such as “Operational Zones” which, from ship to ship and nature of merchandized transported could be totally different.

The Zones

Figure 1: Rolls-Royce unmanned ship project (source: Rolls-Royce)

MARINE


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Norske Veritas (DNV), Korean Register of Shipping (KR) and many other notified bodies in the maritime world.

More power in smaller footprintWith the increase number of embedded electronics, the marine industry has a need for more functionality in a smaller space. Nowadays, ship owners want to equip their vessels with broadband internet connections for both passengers and crew with as much as possible the same features than when ashore.

For instance, position tracking systems are built-in to monitor requiring very compact power supplies, operated in confined environment without fan. Such power supplies have to be designed for conduction cooling,

with high attention on dissipative components placement and optimized conduction cooling (see Figure 2).

For most of the power distribution systems, power units are preferably in cassette format, which is simpler to install, maintain and upgrade. The Marine Cassettes are usually fixed on DIN-Rail though electrical designers within the ship-industry are requiring the power supply to be as well compliant with standalone conduction cooling installation anywhere on the ship, meaning, as for the embedded power supply, the design has to be highly optimized for conduction cooling (see Figure 3).Packaging more power in smaller box, with optimized conduction cooling requires a high degree of integration of the power circuits. The efficiency should be as high as possible, because a small housing also means that the cooling surface is smaller. By using the of the most recent resonant circuits and switching control methods, efficiency up to 95% can be achieved.

Power designers are exploring new technologies such as digital control and the latest generation of Gallium Nitride (GaN) power FETs, targeting higher efficiency and flatter curves, keeping the efficiency high from very low loads to high loads. All new technologies are explored though the nature of the business (often ships are in the middle of oceans and weeks from any lands) requirement for

Figure 3: Powerbox PT577 - Marine grade power supply in cassette format with built-in ORing diodes

Generally two zones are distinguished on a ship; the “bridge and the open deck zone”, and the "general power zone", which basically extends to all other spaces in the ship.

One example of specific requirement per zone is the electromagnetic emission and immunity (EMC). The areas open deck and bridge have extra demands on the electromagnetic emission and immunity (EMC), as a lot of sensitive equipment is positioned here, such as communication, radar and navigation devices. These EMC requirements regarding emissions are well below the known EN55022 Level B and measurement starts already at 10 kHz, instead of the usual 150 kHz.

The limits regarding mechanical and climatic requirements are also higher than for the average industrial application. Vibration levels up to 4g are common, as well as large temperature fluctuations from -25°C and +70°C and high relative humidity where condensation cannot be excluded.

The rulesIt is common to say that; every country with a maritime sector has its own certification-authority with specific demand for local certification, which forces power designers to keep track of the final application where the power supplies will be installed.

In general, there is a common

group of standards and qualification processes that have similar roots for all countries-certification though, from country to country and maritime sub segments, there are as well, a number of very specific requirements increasing complexity. The difficulty is there is no de-facto percentage of “common standards” versus specific, requiring power designers to start any new project by reviewing a large number of documents prior designing anything.

In order to develop a sustainable way-of-working, to ensure that the power solutions can be utilized all over the world, Marine power supplies designers used to combine the requirements from all countries active in marine construction and operation, to establish a cross reference table with equivalence and specific action in case of major deviations (i.e. higher demand on shock and vibration).

Once such equivalence table is established, the toughest requirements of each category is selected and used as reference for

designing, verifying and qualifying the final power supply. This is done in close cooperation with the final customer, reducing risk to under-specified the power supply and to miss final qualification.

From this design methodology, combined with in depth knowledge of local standards and regulations results a test protocol that meet international and local requirements. This test protocol is then applied to all products, simplifying the final approval but as well that the power supply can be used in case of replacement or system-upgrade in any country.

Usually Marine Customers expect the power supplies to comply, certified and be stamped with the type approval logo of Germanischer Lloyd (GL) though, because of the extensive testing to meet EN60945 for extended approvals by Bureau Veritas (BV), Lloyds Register (LRS), America Bureau of Shipping (ABS), Det

Figure 2: Powerbox PT571 - Marine grade power supply designed optimized for conduction cooling in confined environment

Reliable. Available. Now.

tracopower.com

TMF Series5 to 30 Watt fully encapsulated power supply modules for medical application.

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MARINE


extremely high reliability applies and new technologies have to be verified for extreme conditions. This an ongoing process, which is also mandatory for future unmanned ship were maintenance during operation almost impossible.

Reliability and zero downtime are the rule. For that, power supplies should be able to be connected in parallel for redundancy operation. It is very common to add an external ORing block (usually in similar dimensions as the power supplies) which the electricians interconnect to the power supplies. This conventional way tends to disappear and electronics paralleling circuitry built-in the power supply itself. Adding that function into the power unit saved

space in the shelf for more vital equipment but add requirement on power designer to integrate more into smaller packaging.

What’s next in marine?Existing power solutions for the Marine Industry have proven their robustness and international compliances. Power designers are exploring new technology to permanently improve efficiency, decrease power consumption and dissipation. Unmanned ships will require a level of reliability that will be close to the mythic “Fault Zero” and ability for power supplies to be controlled and monitor from a central office (see Figure 4), which could be on the other side of the planet.

For the power designe, it will be

an amazing challenge to combine state-of-the arts technology in switching, thermal management, control and intelligence. We are close to a new era where power supplies will become self-controlled and able to diagnose early sign of failures to apply corrective action. Is that a dream or reality? In my opinion it’s knocking at the door and will soon be there!

Powerboxwwww.prbx.com

References:Maritime Unmanned Navigation Through Intelligence In Networks (MUNIN)http://www.unmanned-ship.org/munin/

Figure 4: Rolls-Royce oX Land-based control center (source: Rolls-Royce)

Special Report:Consumer Electronics

Inside:

Smart dimming technologies...

Step-by-step...

Innovative topology for piezo drivers...

Empowering wireless charger design...

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SPECIAL REPORT : CONSUMER ELECTRONICS



Smart dimming technologies

By: David Gamperl, ams

Proper illumination can help optimize visual impact and power consumption of new HDR TVs

Resolution is the most obvious battleground on which rival television and display manufactur-

ers fight. Consumers have been willing to pay a premium for high-definition HD) displays, and, more recently, for 4k displays. Eventually, ultra-high definition 8k displays are expected to supersede the current generation of high-end TVs.

But with the introduction of High Dynamic Range (HDR) displays, consumers are learning that con-trast also has a strong impact on the viewing experience (see Figure 1). By providing a much greater contrast between the brightest light colors and the deepest, dark-est blacks, an HDR display offers a richer, more exciting and more vivid viewing experience.

The development of new HDR displays, however, poses a power-system design problem for display manufacturers: the requirement for high contrast calls for a very high-brightness back-light, able to reproduce extremely bright por-tions of an image faithfully. But the very high-current display circuit must also be dimmed down to extremely low levels to render the dark portions of the image correct-ly. At the same time, TV manufac-

turers must comply with stringent regulations and guidelines, such as the US Department of Energy’s ENERGY STAR program, which strictly limit the average power consumption of a new TV.

Conventional pulse width modula-tion (PWM) backlight dimming methods alone can achieve no better than a 1:1000 ratio between the highest and lowest current level. If implemented in a high-performance HDR display, a power controller IC with digital PWM dimming alone will result in wast-ed power and impaired picture quality. This is why a new approach to TV backlight power control is needed, to provide a wider spread between peak and minimum

brightness levels, as well as to pro-vide for granular local control of multiple segments of the display screen’s back-light (see Figure 1).

New peak illuminance requirement in HDR displaysDolby, through its Dolby Vision initiative, was the first company to demonstrate the way an HDR TV could perform. Its 2015 demonstra-tion unit had a peak display bright-ness of 4000 nits. By comparison, today’s HD or 4K TVs typically have a peak brightness of around 300 nits. The dramatic increase in peak illuminance both enables the TV to reproduce very bright images faithfully, and extends the contrast between bright and dark displayed images.

The very large contrast ratio is both the factor which makes an HDR display so pleasing to watch, and which makes the power sys-tem design so difficult. This is because, in order to re-produce deep blue, black and grey colors correctly, the backlight needs to be dimmed down to very low levels. This means that if peak brightness is 4000 nits, and a conventional PWM controller can dim at best to 0.1%, then the minimum display brightness is not low enough, and dark blacks will all be rendered as the same greyish color.

In practice, manufacturers of today’s HDR displays are therefore specifying a peak brightness of around 800-1000 nits, a compro-mise which provides for better rendering of very dark colors, but which blunts the appeal of HDR displays by reducing the vividness of the brightest colors. By relying on digital PWM control alone, there is no way out of this problem: a PWM-controlled metal–oxide–semiconductor field-effect transistor (MOSFET) has a certain minimum on-time, which is deter-mined by its turn-off delay and fall time characteristics. The turn-off delay and fall time are basic prop-erties of the power device’s silicon, and these properties prevent PWM controllers from dimming to any less than 0.1% of peak output.

How local dimming helps improve display contrast performanceThe way in which the display is backlit affects contrast, as well as the dimming arrangement. Most

TVs with LED backlights found in homes today are edge-lit, and implement global dimming. This means that if most of the image is bright, the backlight for the entire display is driven at or close to full power; if most of the image is dark, the backlight for the whole display is dimmed to a low level. Global dimming is therefore un-suitable for HDR displays, particu-larly because it is poor at handling the type of image shown in Figure 1, in which both bright and dark portions have to be displayed simultaneously.

In the end, HDR technology calls for direct backlighting with local dimming – a backlight architecture which requires more individual LEDs, more LED channels and a more complex LED driving system. It is therefore more expensive. But by dividing the display’s backlight-ing system into segments – typi-cally today between 16 and 256 in a direct-backlit 47” TV – the back-light brightness can be precisely matched to the content of the image shown in the small square display area served by each seg-ment. Deep dark blues and bright whites can therefore be dis-played simultaneously, with no power wasted on the backlighting of dark portions of the image.

This local dimming approach calls for the LED driver to be synchro-nized to the video or graphics processor (GPU). If the interface between the devices allows, the backlight driver may be directly controlled by the GPU.

Local dimming is a feature enabled by a backlight controller, such as the AS3824 LED from ams. Figure 2 shows how a vertical synchroni-zation signal (VSYNC – a patented feature of ams LED controllers) may be used to mark the start of each new frame, providing a syn-chronization input to a backlight controller. The diagram shows that, in frame 1, a bright image calls for a very high PWM duty cy-cle in segment 1, while segment n has a reduced PWM duty cycle be-cause it is rendering a darker por-tion of the image. Then in frame 2, new video content means that the brightness of the segments must change. Instructions for new PWM duty cycles in segment 1 and seg-ment n are sent by the GPU during frame 1, and the segments’ signals are refreshed with the rising edge of frame 2.

Figure 2 also shows a delay be-tween the rising/falling edge of VSYNC and the rising edge of the PWM signal. In the AS3824 con-

Figure 1: according to AMD’s graphics processor division Radeon Technologies Group, HDR dis-plays should be able to render images with a dynamic range close to that of the human eye. (Image credit: Radeon Technologies Group)

Figure 2: a synchronization signal ensures that the backlight dimming signals are not out of phase with the frame timing

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troller, this delay is programmable, enabling the display manufacturer to compensate for the turn-on de-lay of the LCD’s pixels so that the LEDs begin to draw current exactly at the same time as the pixels are turned on. The result is improved picture quality and minimized power consumption. Delaying the PWM turn-on also reduces the load on the LEDs’ power supply, enabling the system to generate less noise and interference.

Analog dimming: a method for boosting peak brightnessMulti-channel LED controllers – which provides individual control of multiple channels – enable gran-ular local dimming of segments of a display. Up to 32 AS3824 ICs may be daisy-chained via their SPI inter-face to control displays with more than 16 segments (see Figure 3). But manufacturers of HDR dis-plays still face the problem of the contrast ratio. How can they increase peak brightness above 1000 nits while retaining the abil-ity to render very dark colors?

The answer is a patented innova-tion introduced in the AS3824 controller IC: an analogue method for boosting the PWM-controlled current. This can boost the current controlled by the PWM signal by up to a factor of eight over its base level, to illuminate properly the brightest segments of an image.

At the same time, the darkest channel could have an analog LED cur-rent of just 10% of its base value, turned on for the minimum PWM duty cycle – potentially as little as 0.1%. In other words, the dynamic range of the digital PWM part of the dimming scheme is unchanged, but the additional analog scale extends the total (analog + digital) dynamic range (see Figure 4).

The addition of analog dimming is implemented through DACs integrated in the AS3824, which provide a reference voltage output determined by a digital signal input from the display’s video processor or GPU. Amplified, this reference voltage controls the amplitude of the current sup-plied by the FET that powers the channel’s LEDs. In effect, the application of analogue current control produces a power scheme based on simultaneous pulse width modulation and pulse amplitude modulation.

The AS3824 may be used to drive FETs or BJTs with a high current rating. It is important to regulate any external switch-mode power supply so that its output voltage is matched to the

voltage requirements of the LED strings connected to it. Voltage headroom above that required by the FETs controlled by the AS3824 leads to power dissipation, reducing system efficiency.

To enable this, the DC-DC feedback function of the AS3824 works with any kind of DC-DC converter (boost or buck), as well as with other converter architectures such as LLC controllers, by sinking the current across R1 to its feedback (FB) pins (see Figure 5). The timings of the feed-back function are fully programmable via SPI. In manual feedback mode, the output voltage of the SMPS can be adjusted directly by the multi-channel controller. In this manner, the controller is always in full control of the output voltage of the SMPS, thus helping to minimize system power losses.

Sophisticated power control for better contrast ratiosImplementation of LED backlighting control provides for granular, multi-channel control of a direct backlit display screen, as well as an analogue + digital dimming range many times

Figure 3: each daisy-chained AS3824 controller can control the LEDs in up to 16 display segments

Figure 5: the feedback function in AS3824 controllers helps optimize the regulation of the SMPS output voltagewider than that of a typical LED backlight controller using digital-only PWM dimming.

The result is a dramatically im-proved contrast ratio to allow the reproduction of the brightest white colors in some segments of a display at the same time as rendering deep dark blues and grays in other segments, provid-ing a viewing experience dramati-cally better than that in today’s HD and 4k TVs and displays. Resolution revolution Resolution is the most obvious battleground on which rival TV and display manufacturers fight. But with the introduction of High Dynamic Range (HDR) displays, consumers are learning that contrast also has a strong impact on the viewing experience. By providing a much greater con-trast between the brightest light colors and the deepest, darkest blacks, an HDR display offers a richer, more exciting and more vivid viewing experience.

The development of new HDR displays, however, poses a pow-er-system design problem for display manufacturers to solve: the requirement for high contrast

calls for a very high-brightness backlight, able to reproduce ex-tremely bright portions of an im-age faithfully. But the very high-current display circuit must also be dimmed down to extremely low levels to render the dark por-tions of the image correctly.

Conventional PWM backlight dimming methods alone can achieve no better than a 1:1000 ratio between the highest and lowest current level. If imple-mented in a high-performance HDR dis-play, a power controller IC with digital PWM dimming alone will result in wasted power and im-paired picture quality.

Innovative LED power controller technology which overlays analog current control on top of the conventional PWM dimming signal, can provide for a hugely increased dimming scale compared to digital PWM-only control. This enables display manufacturers to achieve much higher contrast ratios than today, for a vastly improved viewing experience.

AMSwww.ams.com

Figure 4: the combination of digital and analog dimming signals, as shown in segment 1/frame 1, provides for a greater contrast ratio between the brightest and the darkest segments of the screen

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SPECIAL REPORT : CONSUMER ELECTRONICS POWER SYSTEMS DESIGN 2017JANUARY/FEBRUARY

Step-by-step

By: Andrea Colognese, Rohm Semiconductor

Addressing the design challenges of stepper motor applications

Combining ultra-precise control with long operating life, stepper motors have

become a critical building block in motion-based applications ranging from white goods to factory automation and robotics to printers and point-of-sale equipment. For the designer, the challenge is to ensure the best combination of performance, functionality and robustness while addressing key functional safety considerations.

At the same time, keeping heat dissipation to a minimum demands optimized efficiency. Addressing these challenges requires careful design of motor drive circuitry. In particular, choice of motor driver ICs and support tools is critical to both application success and speed of development.

A growing marketResearch firm, P&S Market research, predicts that the global stepper motor market will grow from an estimated $1,654.1 million in 2015 to $2,172.5 million in 2022 – showing a CAGR of approximately 3.8%. Target applications for these motors include industrial CNC machines, 3D printing, point-

of-sale systems, valve control, office equipment, factory automation and robotics. And as these applications become smaller and more integrated, the growth of the market for miniature stepper motors is also expected to increase.

In addition, hybrid stepper motors are increasingly being used, particularly in surgical hand tools, pumps and ventilation equipment and this sector is expected to continue to grow along with the packaging sector where stepper motors are heavily used in the integrated machines that offer greater productivity, reliability and efficiency – with reduced costs.

At their simplest level, stepper motors are a special class of brushless DC motors that can be operated via digital control in an open loop configuration without feedback from sensors or encoders. These motors have a different construction to ordinary DC motors. In a simple DC motor, the permanent magnet (stator) is on the outside and the coil (rotor) is on the inside. This is reversed in a stepper motor where the coil (stator) is on the outside and permanent magnets form the rotor.

Key advantages of stepper motors include:

• Availability of full torque

from standstill• Precise and repeatable

positioning (good stepper motors have an accuracy of 3% - 5% per step and this error is non-cumulative from one step to the next)

• Excellent start/stop/reverse response

• Reliability (as there are no contact brushes)

Important application considerationsWhile stepper motors are theoretically easy to control, there are still a number of important considerations for the application designer. Take, for example, speed of motor rotation. With DC motors, speed increases as the applied voltage increases. Stepper motors are “digital” – increasing the voltage level has no effect on rotation speed. The speed of a stepper motor is controlled by the pulse timing – the higher the rate, the faster the motor turns.

However, every motor has a maximum acceptable pulse rate. This, combined with the number of pulses per full turn, determines the maximum possible speed of rotation. The impact of possible reduction in torque at higher rotation speeds (as a result of winding inductance) and ‘motion quality’ – i.e. vibration – must also be taken into account.

The precision and accuracy demanded by the target

application is also important. For those applications that require very high levels of accuracy, for example, control schemes will be expected to support advanced techniques such as micro-stepping, where fractional currents are applied. At the same time, designers must understand how the stepper motors have to accelerate and decelerate in order to achieve optimum performance.

As stepper motor drive schemes are essentially a special application of power

management techniques, consideration needs to be given to the efficiency and safety of the system. In industrial and other electrical noisy environments, for instance, high levels of ESD resistance will be needed for application ‘robustness’. Designers may also need to incorporate circuit protection features such as over current protection (OCP) and current limitation, under- and over-voltage lockout (UVLO/OVLO), and thermal shutdown (TSD).

Integrated stepper-motor drivers

Figure 1: Latest SMDs combine high levels of integrated technology with safety and robustness features

Figure 2: Integrated 36V SMD



In recent years the advent of integrated stepper motor driver (SMD) ICs has helped designers to simplify the implementation of stepper motor control schemes while saving board space and reducing component count. Increasingly these ICs are being made available with development boards and reference designs to build comprehensive ‘support eco-systems’ that further speed the evaluation and prototyping of stepper motor applications.

For example, Rohm’s family of integrated SMDs provides a good illustration of some of the latest developments in this area. Available with a wide range of supply voltages and current capabilities, these advanced devices have been developed using knowledge and experience gained over many years of developing power management solutions. Specifically, ROHMs SMD design philosophy is based on addressing the three fundamental areas of technology, safety and robustness, as illustrated in Figure 1.

The ROHM SMD family for bipolar stepper motors includes 45V high-voltage, 36V standard, micro-step and DC, and low-voltage (15V) drivers with both CLK-IN and PARA-IN variants. Each device uses the company’s established high-density, mixed-signal bipolar+CMOS+DMOS (BCD) semiconductor process technology. This provides the means for integrating highly efficient DMOS power technology with lower power control circuitry and requisite protection functionality in a single device. The integration of a P-channel power device, simplifies the power output stages as the charge pump that would normally be used to drive the high side n-channel is not

needed. This, in turn, ensures a more robust and reliable design.

As an example, Figure 2 shows a schematic of one of a new ROHM solution that will be launched shortly. This high-performance, high-reliability 36V SMD is available with current ratings of 1.0A (BD63710EFV), 1.5A (BD63715EFV), 2.0A (BD63720EFV) and 3.0A (BD63730EFV) and is supplied in a compact 28-pin HTSSOP package.

Each device incorporates a constant current PWM driver for optimized efficiency and a single, integrated power supply that eliminates the need for external power supplies and associated passive components. This built-in power supply saves space and reduces component count when compared to discrete alternatives as well as delivering enhanced EMI performance.

High levels of integrated functionality offer simplicity for

Figure 3: Integrated drive signal translation simplifies the implementation of stepper motor control

Figure 4: Decay mode switching

the designer. As an example, many SMDs require a multi-phase signal from a CPU to control the motor. Using ROHM’s innovative CLK-IN feature, the CPU only needs to provide a single-phase clock signal - all of the low-level phasing is addressed with the on-board translator circuit (see Figure 3).

Typically, when driving a stepper motor, a slow decay in drive current is desirable for smooth torque and low vibration, whereas a fast decay is required for high-speed operation with high pulse rates. As Figure 4 shows, ROHM’s SMDs incorporate a sophisticated mixed decay capability that allows the decay rate to be optimized based on the motor’s characteristics and application requirements. Using mixed-decay mode designers can fine-tune motor performance to

address issues associated with vibration and current waveform distortion. As Figure 2 shows, high levels of protection are provided in the form of built-in UVLO, OVLO, TSD and OCP functionality. The SMDs also incorporate a proprietary ‘Ghost Supply Prevention’ function on all input pins that prevents spurious voltages causing the stepper motor to move in an uncontrolled way when the SMD is unpowered. At the same time, the H-bridge DMOS output ensures a minimum human body model (HBM) ESD resistance of ± 4000V. Design Support - Arduino Evaluation Kit

Selecting advanced and highly integrated devices is only part of the solution. Today’s design engineers are under ever-increasing pressure to deliver

Figure 5: The ROHM Arduino-based EVK allows rapid evaluation and prototyping of stepper motor systems

right-first-time designs in ever-shorter timescales. As a result, the nature of the ‘support eco-system’ available from the SMD manufacturer is becoming an increasingly important aspect of supplier selection.

To support design-in and evaluation of its own SMDs, ROHM is going to launch an Arduino-based evaluation kit (EVK). Designed as a ‘shield’ to plug directly into the Arduino main board, this EVK, which is shown in Figure 5, allows engineers to rapidly evaluate and prototype stepper motor systems.

The EVK will be available in 15 different model variants – each based on a particular ROHM SMD IC. This comprehensive solution covers supply voltages from 8V to 42V, allows up to 2.5A / phase, and supports micro-stepping and single- or multi-phase control of one or two stepper motors. The ‘easy to adapt’ EVK is supplied with a software library and example programs to facilitate a rapid learning curve.

Once the design is proven, engineers can move rapidly from prototype to production phases fully supported by the Bill-of-Materials (BOM) and Gerber-based PCB layouts that are provided with the EVK.

www.rohm.com



Innovative topology for piezo drivers

By: Jim Mutzabaugh, Apex Microtechnology

Improvements in device characteristics have extended their usefulness

Piezoelectric elements have traditionally been used primarily in applications in the audio

industry, operating in the human audio range (nominally 100 Hz to 18 kHz). However, subsequent improvements in device characteristics have extended their usefulness into markets which demand much-higher performance. For example, nuclear instrumentation and bioscience are among the applications which are pushing the performance of these elements.

What is a piezoelectric element?Piezo actuators are unlike any conventional electrical-to-mechanical energy transducers, as they use the piezoelectric effect, where a crystal material will expand very slightly and precisely when a voltage is applied, and return to its original dimensions when the voltage is removed. The complement is also true: a crystal which is subject to an applied stress will generate a voltage, and is used in some non-flame igniters for flammable gases, for example.

Piezo-based actuators are used when a standard electromechanical

motor cannot provide the precise, repeatable micromotion needed without complex gearing (and even with gearing, the system would have slop, backlash, and other shortcomings. They are also used to provide motion with extremely fast and precise rise and fall times, such as in ultrasound transducers, as well as for optical-system lens and fixture micropositioning, among other applications.

The piezoelectric actuator became a mass-market transducer with the introduction and subsequent popularity of inkjet printers several decades ago. Their ability to quickly and precisely stimulate an ink droplet to be ejected is well suited to low-cost ink-on-paper printers at moderate resolution

and medium speed, a good fit for home, small business, and similar situations. They are now used in 3-D printers which are used for rapid prototyping and even moderate production runs.

When the piezoelectric transducer (PZT) is energized, it expands very rapidly by about 0.1% of its nominal length. This expansion (typically on the order of 10-100 µm) generates a precise pressure pulse, which in turn forces the ink or other material out through the orifice of the nozzle, in the case of a printer.

Hard driving Driving a piezo actuator imposes some unique voltage/current requirements. The drive amplifier

for the element must supply high voltage at fast slew rates, and also with precise and repeatable on/off timing. Although a small piezo element looks like a small 1-2 pF load, a larger or multi-element transducer looks like a much-larger load of 100-200 pF, and requires about 50-150 V minimum (and often higher) excitation with a turn-on and turn-off time of several microseconds (and often faster). As a result, the design needs a relatively high voltage, fast-slewing drive circuit which can source/sink current into a capacitive load, which is very different than what is needed for driving conventional electromagnetic motors.Piezoelectric elements (often referred to as PZTs) can be represented by a series-RC combination, where C can be from several hundred picofarads to several nanofarads, with series resistances between several ohms and one to two kilohms. They can be challenging to drive effectively due to their combination of required voltage levels, sink/source current, and equivalent RC values.

The design of the PZT drive-circuit problem was especially difficult when a customer's application simultaneously required these stringent piezo-driver specifications for their military project:

Output Specifications:

• Piezo Drive Voltage: ≥350 V (unipolar) or ±75 V (bipolar);

• Load Voltage Slew Rate: ≥4000 V/µsec (min);

• Peak Driving Current: ≥5 A (peak);

• Controlling Bandwidth: ≥10 MHz;

• Gain Flatness to 10 MHz: ≤2 dB.

System Specifications:• Less than ±12 V input;• PZT element equivalent: 1 nF

in series with 30 Ω;• And, of course, minimum

parts count on the bill of materials.

The specifications appear to be somewhat mutually exclusive:1. High-voltage operation;2. High-current output;3. Wide bandwidth;4. High slew rate.

It is relatively straightforward to design a system that meets any one of these parameters, but the design then needs to compromise

on the other three performance requirements. For example, there are high-voltage (±450 V), low-current (200 mA) op amps, as well as high-current (5 A peak), low-voltage (±200 volts) devices. However, an amplifier with greater than 4000 V/µsec slew rate is currently unavailable in a single op amp, either as a hybrid or monolithic device.

Alternative topology offers a solutionSince there was no conventional approach that would meet the need, it was necessary to investigate the use of a linear push-pull, analog-bridge topology, see Figure 1, for the design:

The 180˚ phase shifter allows each amplifier to be configured in the same mode of operation; in this case, it is the inverting mode. This allows the designer to use identical compensation for each amplifier, since each will be looking into the same load impedance. In contrast, if a single-polarity excitation

Figure 1: One of the useful attributes of the linear push-pull, analog-bridge to-pology is that it enables the use of identical compensation for each amplifier.

Figure 2: The Micro-Cap 11 Spice simulation schematic was critical to performing a full evaluation of the design before any actual prototyping of the design.



voltage was used, each amplifier leg would have to be compensated separately, one way for the inverting leg and perhaps another way for the non-inverting leg.

Further, if noise-gain compensation

is needed for the inverting leg, another method would be required for the non-inverting side, since noise gain compensation is limited in that configuration. In addition, it is much easier to simply generate a low-voltage complementary-

driver voltage.

Note that there are two major advantages when using the linear-bridge circuit, and they enable the design to meet the design criteria:

1. With each leg swinging out of phase with the other, the differential voltage applied to the load is twice that of the output swing of each leg.

2. Measured differentially across the load, the effective slew rate is double that of the single leg.

The Apex Microtechnology PA107 high-voltage power amplifier was selected as the system amplifier. Its primary specifications include:1. Slew Rate: ≥2500 V/µsec;

3000 V/µsec (typical);2. Output Current: 1.5 A

(continuous), 5 A peak (within SOA);

3. Gain Bandwidth: 100 MHz at 1 MHz.

Figure 2 shows the Spice simulation circuit developed using Micro-Cap 11 from Spectrum Software, based on using the PA107 in a dual-bridge topology:

The PA107 uses ±100 V supplies, and the outputs can swing ±90 V, which is within 10 V of either supply rail. The gain-setting resistors and feedback capacitors were selected based up the gain flatness required at 10 MHz, as well as achieving the required slew rate. (The designer must keep in mind that slew rate is also

Figure 3: The simulation of the closed-loop gain of the circuit shows a gain flatness of ±1.1 dB at 10 MHz, at the selected gain.

Figure 4: The output-voltage and slew-rate measurement shows 360 Vp-p drive to the load with ±100-V supplies.

Figure 5: The current through R6 indicates the peak output current, which occurs during the transitions where the charge is being transferred across the capacitive element of the PZT.

Table 1

a function of closed-loop gain.)

During the component-selection cycle, there would be a tradeoff between closed-loop gain, slew rate and bandwidth. The higher the gain, the higher the closed-loop slew rate. However, the higher gain would tend to reduce the closed-loop bandwidth. Conversely, a lower gain would increase the system bandwidth, but reduce slew rate and may approach the ±12-V input needed to drive the complementary outputs to ±90 volts.

After several iterations and manipulating the values of the feedback resistor and capacitor, the optimal gain was determined to be 7.68 (17.71 dB). This kept the input below the 12-V input threshold and also met the 10-MHz gain-flatness and slew-rate requirements.

Figure 3 shows the simulated closed-loop gain plot of the circuit. Note that the selected gain shows a gain flatness of ±1.1 dB at 10 MHz. The excitation voltage applied to the inputs for the transient analysis was ±11.71 V square wave with a 1 µsec period and a 50% duty cycle.

Figure 4 shows the simulations for the output-voltage and slew-rate measurement. The ±90 V output on each leg using ±100-V supplies meant that the circuit could apply

360 Vp-p to the PZT load. The designer does have to consider the peak output current during the transitions where the charge is being transferred across the capacitive element of the PZT. That situation was simulated by looking at the current through R6, Figure 5. The measured current through the resistive element of the piezoelectric element was 4.91 A.

Results and conclusionsThe comparison of the project’s requirements with the simulated

results shows the validity of the topology and design approach:

By the judicious selection of topologies and components, these very stringent design requirements were met. This result was achieved through the combination of the performance characteristics of the analog-bridge topology and the overall high-performance specifications of the PA107 high-voltage power amplifier.

Apexwww.apexanalog.com

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Empowering wireless charger design

By: Eko Lisuwandi, Linear Technology

Monolithic full-bridge AutoResonant transmitter IC simplifies wireless battery charger systems

The use of batteries in everyday devices is getting more ubiquitous. In

many of these products, a charging connector is difficult or impossible to use. For example, some products require sealed enclosures to protect sensitive electronics from harsh environments and to enable for convenient cleaning or sterilization. Other products may simply be too small to include a connector, and in products where the battery-powered application includes movement or rotation, forget about charging with wires. Wireless charging adds value, reliability and robustness in these and other applications.

There are many ways to deliver power wirelessly.

Across a short distance of less than a few inches, capacitive or inductive coupling is commonly used. In this article, solutions using inductive coupling are discussed.

In a typical inductively coupled wireless power system, an AC magnetic field is generated by a transmit coil, which then induces an AC current in a receive coil just like a typical transformer system. The main difference between a transformer system

and a wireless power system is that an air gap or other non-magnetic material gap separates the transmitter and receiver. Furthermore, the coupling between the transmit coil and the receive coil is typically very low. Whereas a coupling of 0.95 to 1 is common in a transformer system, the coupling coefficient in a wireless power system varies from 0.8 to as low as 0.05.

Wireless charging basicsA wireless power system is

composed of two parts separated by an air gap: transmit (TX) circuitry, including a transmit coil, and receive (RX) circuitry, including a receive coil. When designing a wireless power

battery charging system, a key parameter is the amount of power that actually adds energy to the battery.

This received power depends

on many factors including:• Amount of power being transmitted• Distance and alignment between the transmit coil and the receive coil, commonly represented as the coupling factor between the coils• Tolerance of the transmit and receive components

The main goal in any wireless power transmitter design is the ability for the transmit circuit to generate a strong field to guarantee delivery of the required

Figure 1: The LTC4125 driving a 24µH transmit coil at 103kHz, with 1.3A input current threshold, 119kHz frequency limit with LTC4120-4.2 as a 400mA single-cell charger at the receiver

Figure 2: LTC4125 AutoResonant Drive

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received power under worst-case power transfer conditions. However, it is equally important to avoid thermal and electrical overstress in the receiver during best-case conditions. This is especially important when output power requirements are low, and the coupling is great. An example would be a battery charger when the battery is fully charged with an RX coil placed close to the TX coil.

A Simple but Complete Transmitter Solution Using the LTC4125For our example, we’ll use the LTC4125 transmitter IC, designed to pair with one of the various battery charger ICs in Linear Technology’s portfolio as the receiver, for example the LTC4120 – a Wireless Power Receiver and Battery Charger IC (see Figure 1).

The LTC4125 comes with all of the features necessary for a simple, powerful and safe wireless power transmitter circuit. In particular, it has the ability to adjust its output power, depending on the receiver load requirement as well as to detect the presence of a conductive foreign object.

As mentioned earlier, the transmitter in a wireless battery charger system needs to generate a strong magnetic field in order to guarantee delivery of power under worst-case power transfer conditions. To meet this goal, the LTC4125 employs a proprietary AutoResonant technology.

The LTC4125 AutoResonant Drive ensures that the voltage at each SW pin is always in phase with the current into the pin. Referring to Figure 2: when current is flowing from SW1 to SW2, switches A and C are on while switches D and B are off, and vice versa in reverse. Locking the driving frequency cycle by cycle with this method ensures that the LTC4125 always drives the external LC network at its resonant frequency. This is true even with continuously changing variables that affect the

resonant frequency of the LC tank such as temperature and the reflected impedance of a nearby receiver.

With this technology, the LTC4125 continually adjusts the driving frequency of the integrated full bridge switches to match the actual resonant frequency of the series LC network. In this fashion, the LTC4125 is able to efficiently build a large amplitude AC current in the transmitter coil without the need of a high DC input voltage, nor of a highly

precise LC value.

The LTC4125 also adjusts the pulse width of the waveform across the series LC network by varying the duty cycle of the full bridge switches. By adjusting the duty cycle higher, more current is generated in the series LC network and therefore more power is available to the receiver load.

Figure 3: LTC4125 Pulse Width Sweep – Voltage & Current in the TX Coil Increases as the Duty Cycle Is Increased

Figure 4: Comparison of the LTC4125 Transmitter LC Tank Voltage Frequency With & Without the Presence of a Conductive Foreign Object

The LTC4125 performs a periodic sweep of this duty cycle to find the optimum operating point for the load condition at the receiver. This Optimum Power Point Search allows operation tolerant of a large air gap and misalignment of the coils while avoiding thermal and electrical overstress to the receiver circuit in all cases. The period between each sweep is easily

programmable with a single external capacitor (see Figure 3).

The system shown in Figure 1 is quite tolerant of considerable misalignment. When the coils are misaligned significantly, the LTC4125 is able to adjust the generated

magnetic field strength to

ensure that the LTC4120 receives the full charge current. In the system shown in Figure 1, up to 2W can be transmitted at a distance of up to 12mm.

Foreign conductive object detectionAnother essential feature of any viable wireless power transmit circuit is the ability to detect the presence of a conductive

Figure 5: LTC4125 drivingn a 24µH transmit coil at 103kHz, 119kHz frequency limit in a wireless power system with LTC3652HV as a 1A single cell charger

Figure 6a(right) 6b(left): Typical Complete Wireless Power Transmitter Board Using LTC4125

44 WWW.POWERSYSTEMSDESIGN.COM


foreign object placed in the magnetic field generated by the transmit coil. A transmit circuit designed to deliver more than a few hundred milliwatts to the receiver needs the ability to detect the presence of conductive foreign objects in order to prevent eddy current from forming in the object and causing undesirable heating.

The AutoResonant architecture of the LTC4125 allows a unique method for the IC to detect the presence of a conductive foreign object. A conductive foreign object reduces the effective inductance value in the series LC network. This causes the AutoResonant driver to increase the integrated full bridge driving frequency.

The graph in Figure 4 contrasts the frequency of the voltage developed across the transmit coil, with and without the presence of a conductive foreign object.

By programming a frequency limit via a resistor divider, the LTC4125 reduces the driving pulse width to zero for a period of time when the AutoResonant drive exceeds this frequency limit. In this fashion, the LTC4125 stops delivery of any power when it detects the presence of a conductive foreign object.

Note that by using this frequency shift phenomenon to detect the

presence of a conductive foreign object, the detection sensitivity can be directly traded off with the component tolerance of the resonant capacitor (C) and the transmit coil inductance (L). For a typical 5% initial tolerance on each of the L and C values, this frequency limit can be programmed at 10% higher than the expected natural frequency from the typical LC value for a reasonably sensitive foreign object detection and robust transmitter circuit design. However, tighter tolerance 1% components can be used with the frequency limit set at only 3% higher than the typical expected natural frequency for a higher detection sensitivity while still maintaining the robustness of the design. Power level flexibility & performanceWith some simple resistor and capacitor value changes, the same application circuit can be paired with a different receiver IC for higher wattage charging (see Figure 5). Due to the high efficiency full bridge driver on the transmit circuit as well as the high efficiency buck switching topology of the receive circuit, overall system efficiency as high as 70% can be achieved.

This overall system efficiency is calculated from the DC input of the transmit circuit to the battery output of the receive circuit. Note that the quality factor of the two coils, as well as their

coupling, is just as important to the overall efficiency of the system as the rest of the circuit implementation.

All of these features in the LTC4125 are achieved without any direct communication between the transmitter and receiver coils. This allows for a simple application design, covering various power requirements up to 5W as well as many different physical coil arrangements.

Figure 6 showcases the small overall size of the typical LTC4125 application circuit as well as its simplicity. As mentioned before, most of the features are customizable using external resistors or capacitors.

Powering forwardAdvanced solutions like the LTC4125 provide all of the features necessary to make a safe, simple and highly efficient wireless power transmitter. The AutoResonant technology, Optimum Power Search and the Conductive Foreign Object detection via frequency shift ease the design of a full-featured wireless power transmitter with excellent distance and alignment tolerance. The LTC4125 is a simple and exceptional choice in a robust wireless power transmitter design.

Linear Technologywww.linear.com

By: Alix Paultre, Editorial Director, PSD

Consumer ElectronicsLas Vegas

Toyota touted their next-generation car and its advanced infrastructure

If you are using your cell phone to control your human-carrying drone while a passenger, are you piloting it?

Advanced sports monitoring will also incorporate motion capture

For those who want to keep vinyl alive, here's a turntable with a built-in tube amplifier.

ROUNDupCES


46

ROUNDupCES


large-scale displays are now as good as the TV in your living room

It's bad enough my friends beat me at chess

The elusive Faraday Future car, a step closer to reality

High-end automotove audio is also still very popular in certain circles

Insanely flat and vivid OLED displays were everywhere

48

PAULTREonPower


POWER SYSTEMS DESIGN

By: Alix Paultre, Editorial Director, PSD

The design explosion

Let’s continue the thought

we began with at the front

of the issue, as simply

saying that it’s good to

have a lot of product development,

even if some of it is on stuff that

is a little crazy, leaves a lot to be

said. How does a laundry-folding

robot help humanity? Will having a

toothbrush that sends me emails

about the performance dynamics of

my brushing prowess bring about a

better world? Kinda.

This is a fantastic time to be an

engineer. Hell, it’s a great time to be

an intelligent creative person with

even a modicum of resources, as

this is a golden age of design and

development. There hasn’t been a

time in history where technology

and tools have been more open

to people. Today a person with

an idea that is at least based on

physical reality can take that idea

and manifest it in a product with

a minimum of fuss, compared to

legacy situations.

This ease of entry into the

development space has manifested

itself in some ways as the rapidly-

growing Maker movement, as

interested people from all walks of

life take these readily-available tools

and technologies to create things

that only they can see and bring

them into the real world for all to

enjoy (or not). The other ways this

has manifested itself is less flashy,

as legacy systems rapidly modernize

using the new devices and abilities.

But both are important.

The explosion of devices, some

frivolous, moves the ball forward in

important ways. First, by capturing

the imagination of the public, the

more whimsical devices help advance

technology adoption, showing people

ways advanced technology can help

them. That clothes-folding machine

may never hit the store shelves, but

the shiny future it helped paint in the

mind’s eye of the public is invaluable

to an attitude of acceptance and

optimism.

Another important way gadget

generation helps the industry is that it

provides work for the manufacturing

community, from electronic design

engineers to packaging specialists

and advertising copyrighters. That

bad-hair predicting hairbrush

may have been a fad, but it kept a

company alive with a novel product

while they were working on that more

reasonable project with the longer

development cycle. That benefit

cascades through the industry as the

various circles of business support

leverage one another into action.

The last is very important to the

electronics industry, and that is

the ability to expand and develop

our manufacturing base and its

capabilities. Things like small hi-

res displays, flex circuits, improved

packaging, and more sophisticated

manufacturing techniques all cost

a lot of money to develop and

nurture, and nothing improves

commercialization like volume.

Every widget created increases the

products moving through assembly

lines, enabling volumes of scale to

be applied to the latest technologies,

bringing their prices down faster and

speeding adoption.

PSD

www.powersystemsdesign.com

ROHM Semiconductor, a leading enabler of SiC, has been focused on developing SiC for use as a material for next-generation power devices for years and has achieved lower power consumption and higher efficiency operation.

Energy Efficient and SustainableSystems with SiC

ROHM is the first semiconductor supplier worldwide who succeeded to provide SiC Trench MF Technology in mass production

Local system specialists provide comprehensive application support

In-House integrated manufacturing system from substrate to module

SiC WaferSBD, MOSFET,Discrete and Modules

Leading Technology Full System Level Support

Full Quality and Supply Chain Control Full Line-up

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SMALLERSTRONGERFASTER

Linear Technology ASM STANDARD PAGE TRIM SIZES : 8 x 10.5” Minimum 8.5 x 11.25” / 216mm x 286mm Maximum

Agency contact: Jon MiwaPhone: 926-642-3053Email: [email protected]

Active Area <300mm2

LTC3119

2.5V to 18VVIN

GND

VOUT0.8V to 18V

Info & Free Samples

, LT, LTC, LTM, Linear Technology, the Linear logo and PowerPath are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

www.linear.com/product/LTC31191-800-4-LINEAR

Broad Line of Monolithic Buck-Boost Converters

Our LTC3119 brings a new level of performance and integration to our growing family of monolithic Buck-Boost converters. Its internal switches can deliver up to 5A of output current while having fast transient response due to its current mode control and a compact solution footprint. Its 2.5V to 18V input range is ideal for single to multicell battery configurations as well as poorly regulated 5V or 12V adapters and the output can be set to any voltage from 0.8V to 18V. The LTC3119 has a low 35µA quiescent current, programmable switching frequency from 400kHz to 2MHz and can deliver up to 98% conversion efficiency allowing design flexibility and a low noise output.

Internal FETs & Sense Resistor Simplify Design

18V/5A Monolithic Buck-Boost

PartNumber Comments

VINRange

(V)

VOUTRange

(V)

IOUT inBuck Mode

(A)

LTC3114-1 2.2 to 40LTC3118LTC3115LTC3112LTC3113

LTM8054LTM8056LTM8055LTM4607

LTM4609

LTM4605

2.2 to 182.7 to 402.7 to 151.8 to 5.5

5 to 365 to 585 to 36

4.5 to 36

4.5 to 36

4.5 to 20

2.7 to 402 to 18

2.7 to 402.5 to 141.8 to 5.5

1.2 to 361.2 to 481.2 to 360.8 to 24

0.8 to 34

0.8 to 16

122

2.54

5.45.58.510

10

12

IQ = 30μA, Efficiency up to 96%, Programmable Output CurrentDual Input PowerPath™, Efficiency up to 94%IQ = 30μA, Efficiency up to 95%, UVLOIQ = 50μA, Efficiency up to 95%, OVP, Output DisconnectIQ = 40μA, Efficiency up to 96%, Output Disconnect

15mm x 11.25mm x 3.42mm BGA Package, Internal InductorLTC3119 2.5 to 18 0.8 to 18 5 IQ = 35μA, Efficiency up to 98%, MPPC

15mm x 15mm x 4.92mm BGA Package, Internal Inductor15mm x 15mm x 4.92mm BGA Package, Internal Inductor15mm x 15mm x 2.82mm LGA Package, External Inductor15mm x 15mm x 2.82mm LGA or 15mm x 15mm x 3.42mm BGA Package, External Inductor15mm x 15mm x 2.82mm LGA Package, External Inductor

Linear’s European Sales Offices: Finland +358-46-712-2171France +33-1-56701990 Germany +49-89-9624550 Italy +39-039-5965080 Sweden +46-8-623-1600 UK +44-1628-477066 Fran-chised Distributors: Pan-European Farnell Austria +49-89-9624550 Belgium +49-89-9624550 Austria Arrow, Digi-Key Denmark Arrow, Digi-Key Eastern Europe Arrow, Digi-Key, Setron Finland Digi-Key,

Fintronic Oy France Arrow, Digi-Key Germany Arrow, Digi-Key, Setron Ireland Arrow, Digi-Key Israel Avnet Italy Arrow, Digi-Key Netherlands Arrow, Digi-Key Norway Arrow, Digi-Key Russia Arrow, Digi-Key, Gamma, PT Electronics Spain Arrow, Digi-Key Sweden Arrow, Digi-Key Switzerland Arrow, Digi-Key Turkey Arrow, Digi-Key UK Arrow, Astute Electronics (Military only), Digi-Key

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