CONTENTS

www.power-mag.com Issue 4 2015 Power Electronics Europe

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Editor Achim ScharfTel: +49 (0)892865 9794Fax: +49 (0)892800 132Email: achimscharf@aol.com

Production Editor Chris DavisTel: +44 (0)1732 370340

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Eastern US Karen C Smith-Kerncemail: KarenKCS@aol.comWestern US and CanadaAlan A KerncTel: +1 717 397 7100Fax: +1 717 397 7800email: AlanKCS@aol.com

Italy Ferruccio SilveraTel: +39 022 846 716 Email: ferruccio@silvera.it

Japan:Yoshinori Ikeda, Pacific Business IncTel: 81-(0)3-3661-6138Fax: 81-(0)3-3661-6139Email: pbi2010@gol.com

TaiwanPrisco Ind. Service Corp.Tel: 886 2 2322 5266 Fax: 886 2 2322 2205

Publisher & UK Sales Ian AtkinsonTel: +44 (0)1732 370340Fax: +44 (0)1732 360034Email: ian@dfamedia.co.ukwww.power-mag.com

Circulation and subscription: Power ElectronicsEurope is available for the following subscriptioncharges. Power Electronics Europe: annual chargeUK/NI £60, overseas $130, EUR 120; single copiesUK/NI £10, overseas US$32, EUR 25. Contact: DFA Media, 192 The High Street, Tonbridge, Kent TN9 1BE Great Britain. Tel: +44 (0)1732 370340. Fax: +44 (0)1732 360034. Refunds on cancelledsubscriptions will only be provided at the Publisher’sdiscretion, unless specifically guaranteed within theterms of subscription offer.

Editorial information should be sent to The Editor,Power Electronics Europe, PO Box 340131, 80098Munich, Germany.

The contents of Power Electronics Europe aresubject to reproduction in information storage andretrieval systems. All rights reserved. No part of thispublication may be reproduced in any form or by anymeans, electronic or mechanical includingphotocopying, recording or any information storageor retrieval system without the express prior writtenconsent of the publisher.

Printed by: Garnett Dickinson.

ISSN 1748-3530

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Automotive Opportunities for Power GaNThis article includes studies of the market opportunity, current performance and

projected performance of very large area GaN devices that have applicability to

the automotive market. Comparisons are made regarding the performance

differences between SiC, GaN, and IGBT devices. A yieldable large area 650

V/100 A GaN device is described. Girvan Patterson, GaN Systems Inc,

Ottava, Canada

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Digital Control Limits InrushCurrentAC/DC power supplies and rectifiers employ large bulk capacitors. During power-

up, these capacitors require large amount of current to charge up resulting in a

large inrush current. This inrush current creates limitations in the operation of

power devices and interference of those devices with power line and circuit

breakers. It also affects the reliability of power system due to overstress caused by

instantaneous but huge surge in initial current at power up. Known solutions to

limit inrush current [1, 2] require resistors or conventional NTC thermistors which

contribute significant power loss and decrease the efficiency. Our approach has

two objectives: first, to illustrate advantages of digital power control that

overcomes many of the disadvantages of the existing technology and second, to

raise interests in digital control of the high power converters, stimulating

development of its next generation. Anatoliy Tsyrganovich,

Leonid Neyman, and Abdus Sattar, IXYS Corporation, USA

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Making Battery Fuel Gauges Tell the TruthA new and highly accurate technique for battery fuel gauging could help users of

mobiles and other portable devices avoid the inconvenience and frustration of

unexpected system shutdowns. Steve Sheard, ON Semiconductor, USA

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48 V GaN Point-of-Load ConverterGallium nitride (GaN) devices have hit the power electronics market with force. By

offering lower capacitances and zero reverse recovery, they promise to

dramatically improve efficiency and open up new markets. One of these new

opportunities is powering high-current loads directly from the 48 V bus, common

in server and telecommunications environments. This approach provides

advantages over the traditional two-stage solution of using a bus converter

followed by a point-of-load (PoL) voltage regulation module (VRM). The single-

stage provides a more-efficient solution while providing improved transient

response and form factor improvements. Michael Seeman, Systems and

Applications Engineering Manager, Texas Instruments, Dallas, USA

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ProductsProduct update.

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Website Product Locator

Novel Low InductivePhase-Leg IGBT ModuleEases ParallelingAt PCIM 2015 ABB has introduced the LinPak, a newopen standard phase-leg type IGBT module with arating of 1700 V and 2 x1000 A and a footprint of 100mm x 140 mm. This type of module will set a newstandard in power density. We designed the LinPak toaccommodate chipsets from 1200 V up to 3300 V.The LinPak IGBT module features an exceptionally lowstray inductance enabling the full utilization ofadvanced low switching loss IGBT chipsets and evenfuture full Silicon Carbide switch solutions. In additionthe LinPak is ideally suited for parallel connection withnegligible derating, thus a large range of inverter powercan be realized with just one module type. Togetherwith the open standard concept this module fulfills along wish of the industry in nearly all high powersegments such as traction & CAV (commercial,construction and agricultural vehicles), wind-power &solar and industrial drives to name a few. Full story on page 15.

Cover supplied by ABB Switzerland Semiconductors.

COVER STORY

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Industry News

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Market NewsPEE looks at the latest Market News and company

developments

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Making Battery Fuel Gauges Tell the TruthA new and highly accurate technique for battery fuel gauging could help users of mobiles andother portable devices avoid the inconvenience and frustration of unexpected system shutdowns. Steve Sheard, ON Semiconductor, USA

Battery-powered mobile devices havebecome vital to modern life. Users oftenneed to continue operating their devices atlow battery levels, and can sufferinconvenience if the system suddenly shutsdown despite indicating that a few percentof battery energy still remains. Given theimportance of knowing accurately howmuch energy is remaining in the battery atany time, accurate battery “fuel-gauging” ishighly important. However, the coulomb-counting technique traditionally used inportable devices is not only inaccurate,leading to a high risk of unexpected

shutdown, but is also subject totemperature-related errors and consumesprecious battery energy that may be betterutilized to power other functional circuitry.

Fuel gauging by coulomb countingCoulomb counting uses a precisioncurrent-sensing resistor to monitor thebattery output current continuously. Thecurrent is integrated over time, and theresult is compared with the knownmaximum battery charge to calculate theremaining charge available.Coulomb counting is inherently

inaccurate because it is unable to detectbattery self-discharge events, since the self-discharge current does not pass throughthe coulomb counter’s sense resistor.Moreover, self-discharge events tend toincrease the ambient temperature, whichchanges the resistance of the senseresistor thereby further impairing accuracy.In addition, the battery has to be fullycharged every time for an accuratecalibration. Further disadvantages ofcoulomb counting include the relativelyhigh cost of the precision sense resistor, aswell as the precious battery energydissipated by this resistor as the sensecurrent passes through continuously.A coulomb counter may be accurate to

within around 8 %. Hence if the indicatorsuggests 10 % of charge is remaining, thereal value may be as little as 2 %. With sucha level of inaccuracy, the user may becomeanxious about the remaining battery lifeeven if the indicator shows 20 % or so ofcharge remaining. The worry of suddenplummets in indicated battery life only serveto add to the general sense of mistrust ofthe status information presented.As the market waits patiently for

improvements in battery technology (orindeed resigned to the status quo), andequipment designers conceive increasinglycomplex power-management schemes toconserve every possible scrap of batteryenergy, it is extremely important that thefuel gauge provides an accurate reading forthe user while itself consuming as little ofthe battery’s energy as possible.

A better wayON Semiconductor has developed aproprietary method for calculating theremaining battery energy based on thevoltage measured across the battery usinga precision analogue-to-digital converter(ADC). Figure 1 illustrates a basicapplication circuit showing the majorfunctional blocks of a fuel-gauging systemusing this technique.A reference table describing the voltage-

vs-capacity characteristic of the batterytechnology being monitored is stored inmemory. By comparing the measured

Figure 1: Voltage-sensing method for battery fuel gauging

Figure 2. The remaining battery capacity is inferred from the measured voltage by referring to thebattery reference table

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voltage with values stored in the table, theremaining battery capacity can be calculated.Figure 2 illustrates the principle: if themeasured voltage is 4.0 V, comparison withthe reference table suggests 75 % of batterycharge is remaining.

Repeated voltage measurements aretaken at known time intervals. The batterytemperature is also monitored. The timeremaining before the battery will becompletely depleted can then becalculated, based on the voltage andtemperature measurements and thechanges in the voltage recorded at theknown time intervals. More frequentreadings are taken at lower batteryvoltages, to ensure accurate predictions asthe remaining battery life becomes shorter.

By measuring the voltage across thebattery pack, this approach is able to takeaccount of battery self-discharge events.Moreover, the battery does not need to befully charged for calibration. The remainingbattery life can be calculated accuratelyeven if the battery is only charged to 50 %.

Because measurements are taken atintervals, the monitoring circuitry does notneed to be active continuously. This allowsthe fuel gauging circuitry to enter energy-

saving sleep mode in betweenmeasurements. The active powerconsumption can also be reduced, incomparison with a conventional coulombcounter, since no sense resistor is needed.

Operation at low ambient temperatures isknown to have a significant effect on theperformance of Li-ion batteries. In particular,the battery impedance changes as thetemperature falls to 0°C or lower, resultingin increased battery voltage drop whendischarge current flows. A unique correctionalgorithm in its LC709203F battery-voltagesensing fuel gauge IC helps ensure fuel-gauging accuracy remains within 2.8 % overa wide ambient temperature range and atall battery voltages.

Experimental resultsTo compare fuel gauging using theLC709203F with the performance of acoulomb counting circuit, a smartphonewith a new battery was adapted to allowthe positive and negative batteryconnections and the thermistor output ofthe battery pack to be connected to thedevice while allowing the smartphone’sbuilt-in fuel gauge to continue operating.Data loggers were used to record the

output of the built-in fuel gauge, which wasmonitored via the smartphone I2C bus, andthe output of the LC709203F. Thesmartphone was placed in a constant-temperature tank at 0°C, and operated inairplane mode with the backlight turned on.Figure 3 illustrates the experimental setup.

Figure 4 shows the results of thecomparison. The accuracy achieved usingthe LC709203F is better than 2.8 % forthe duration of the test, and is better than2 % at the lowest levels of remainingbattery energy. The standard fuel-gaugesystem operates with varying levels of errorand reaches its highest level of more than6 % as battery energy nears depletion.From the user’s point of view, greateraccuracy is desirable at lower levels ofbattery energy, to be able to predict whenthe equipment may shut down.

Size and power savingsThe LC709203F allows effective fuelgauging using only one externalcomponent, whereas alternative devicesmay require two to five, or as many as 14,additional components. This delivers avaluable saving in Bill Of Material costs anddesign time, and also increases reliability.Moreover, the 1.76mm x 1.6mm packageis about 45% smaller than alternativedevices. Combined with the reducedcomponent count, this allows the overallPCB footprint of the fuel gauge circuit tobe reduced by around 77%. This canrepresent a crucial gain for smartphonedesigners who continually battle tosqueeze in all the design elements toprovide the functionality and user interfacedemanded by consumers, leaving littlespace for the components that actuallymake it all happen.

Total power consumption is also lower.The LC709203F operating current of 15µA is approximately 1/10th that of theclosest competing device, which draws118 µA. In addition to this improvement ofover 87 % in active consumption, theLC709203F draws up to 60 % lowercurrent in sleep mode.

ConclusionThe relatively poor accuracy ofconventional coulomb-counting batteryfuel gauges leaves users of today’s mobiledevices vulnerable to inconvenientinterruptions when using their devices,particularly when working close to thelimits of remaining battery energy. A newtechnique that uses precision sensing ofbattery voltage, with error correction andtemperature compensation built in,promises a more accurate, cost-effectiveand energy-efficient solution that willenable users to manage their mobilebatteries more effectively.

Figure 3. Comparison of built-in smartphone battery fuel gauge and voltage measurement techniqueusing LC709203F

Figure 4.Results of

comparison test

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