three-phase metrology with enhanced esd protection and

Load

Phase A Phase

C

Phase B

Neu

tral

+

-

Sx, COMx

MSP430F67791A

R33

32768 Hz

XIN

XOUT

GPIOs

TOTAL

AB

kWh

LCDCAP

PULSE LEDs

ZigBee Radio(CC2530)

UART RX

UART TX

UART 9600 bpsUART RX

UART RX

UART TX

6' Modulator

6' Modulator

-

Source From Utility

CT

Phase APha

se B

Phase C

6' Modulator

6' Modulator

6' Modulator

+

+

-

+

-

+

-

+

-

RSTVCC

VSS

6' Modulator

+

-

+

-

6' Modulator

¯û

24

VREF

IA

IB

IC

VA

VB

VN

VN

VC

VN

IN

Neu

tral

CT

CT

CT

Capacitive power supply(TPS54060)

UART TX

TI DesignsThree-Phase Metrology With Enhanced ESD Protectionand Tamper Detection

TI Designs Design FeaturesTI Designs provide the foundation that you need • Three-Phase Meter With Tamper Detection Whichincluding methodology, testing, and design files to Exceeds Class 0.2 Accuracy Requirements fromquickly evaluate and customize the system. TI Designs ANSI and IEChelp you accelerate your time to market. • Passed IEC 61000-4-2 Level-4 Air Discharge Tests

[1] (See Below for Details)Design Resources• TI Energy Library Firmware Calculates All Energy

Measurement Parameters Including Active andTIDM-3PHMTR-TAMP- Design Folder Reactive Power and Energy, RMS Current andESDVoltage, Power Factor, and Line FrequencyMSP430F67791A Product Folder

TPS54060 Product Folder • Support for ZigBee® Communication to In HomeDisplay or Connections to Wi-Fi®, Wireless M-Bus,CC2530 ` Product Folderand IEEE-802.15.4g Add-On CommunicationsCC2530EMK Tools FolderModulesTIDM-LOWEND-IHD Tools Folder

• Automated or Manual Switching Between Main andAuxiliary Power Sources for Metrology Engine

ASK Our E2E ExpertsFeatured ApplicationsWEBENCH® Calculator Tools

• Metering• Street Lighting

An IMPORTANT NOTICE at the end of this TI reference design addresses authorized use, intellectual property matters and otherimportant disclaimers and information.

All trademarks are the property of their respective owners.

1TIDU817–March 2015 Three-Phase Metrology With Enhanced ESD Protection and TamperDetectionSubmit Documentation Feedback

Copyright © 2015, Texas Instruments Incorporated

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http://www.ti.com/product/tps54060

http://www.ti.com/product/cc2530

http://www.ti.com/tool/CC2530EMK

http://www.ti.com/tool/TIDM-LOWEND-IHD

http://e2e.ti.com/

http://e2e.ti.com/support/development_tools/webench_design_center/default.aspx

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http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=TIDU817

System Description www.ti.com

1 System DescriptionThis design implements an ANSI/IEC Class 0.2 three-phase energy meter with enhanced ESD protection.The design also features tamper detection to limit the feasibility of energy theft and communicationsthrough ZigBee™ connectivity. The e-meter system on chip SoC is used to perform all metrology functionsand sends active power results to the CC2530EM add-on board. Developers can use the companion InHome Display TI design (TIDM-LOWEND-IHD) to display results remotely [2].

The design guide has a complete metrology source code provided as a downloadable zip file.

1.1 MSP430F67791AFor sensing and calculating the metrology parameters, the MSP430F67791A e-meter SoC is used. Thisdevice is the latest metering system on chip (SoC) that belongs to the MSP430F67xxA family of devices.This MSP430F67xxA family of devices offer enhancements when compared to the previous non-AMSP430F67xx devices such as the MSP430F67791. One of these enhancements addresses improvedESD robustness (see the Differences Between MSP430F67xx and MSP430F67xxA Devices applicationnote for more details on this change as well as other changes compared to the non-A MSP430F67xxdevices). These ESD enhancements can enable increased ESD immunity when compared to the previousmeters based on the non-A MSP430F67xx devices.

In regard to metrology, the MSP430F67791A energy library software has support for calculation of variousparameters for up to three-phase energy measurement. The key parameters calculated during energymeasurements are: RMS current and voltage; active power, reactive power, and energies; power factor;and frequency. These parameters can be viewed either from the calibration graphical user interface (GUI)or liquid crystal display (LCD).

1.2 CC2530For ZigBee communication, the CC2530EMK evaluation kit is used. Place the board of the kit into theEVMs RF connector to enable ZigBee communication. The F67791A e-meter software automaticallypackages the active power readings into a packet. This packet is then sent to the CC2530 that isconnected to the RF connector of the design.

The TIDM-LOWEND-IHD TI design can be used as a receiver. When this receiver is used, the CC2530 onthe IHD430 receives the packet from the CC2530 on the design and displays the packet on the IHD430LCD.

1.3 TPS54060The TPS54060 is used in the power supply to help provide a 3.3-V output from an input mains voltage of120/230-V RMS AC at 50/60 Hz. Figure 8 shows how the TPS54060 is used to create the 3.3-V outputfrom the 120/230-V RMS AC input.

2 Three-Phase Metrology With Enhanced ESD Protection and Tamper TIDU817–March 2015Detection Submit Documentation Feedback


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http://www.ti.com/lit/pdf/slaa666


Load

Phase A Phase

C

Phase B

Neu

tral

+

-

Sx, COMx

MSP430F67791A

R33

32768 Hz

XIN

XOUT

GPIOs

TOTAL

AB

kWh

LCDCAP

PULSE LEDs

ZigBee Radio(CC2530)

UART RX

UART TX

UART 9600 bpsUART RX

UART RX

UART TX

6' Modulator

6' Modulator

-

Source From Utility

CT

Phase APha

se B

Phase C

6' Modulator

6' Modulator

6' Modulator

+

+

-

+

-

+

-

+

-

RSTVCC

VSS

6' Modulator

+

-

+

-

6' Modulator

¯û

24

VREF

IA

IB

IC

VA

VB

VN

VN

VC

VN

IN

Neu

tral

CT

CT

CT

Capacitive power supply(TPS54060)

UART TX

www.ti.com Block Diagram

2 Block Diagram

Figure 1. TIDM-3PHMTR-TAMP-ESD System Block Diagram

Figure 1 shows a block diagram that displays the high-level interface used for a three-phase energy meterapplication that uses the MSP430F67791A device. A three-phase four-wire star connection to the ACmains is shown in this case. In the diagram, a current sensor connects to the current channel and asimple voltage divider is used for the corresponding voltage. The CT has an associated burden resistorthat must be connected at all times to protect the measuring device. The selection of the CT and theburden resistor is made based on the manufacturer and current range required for energy measurements.The CTs can easily be replaced by Rogowski coils with minimal changes to the front-end. The choice ofvoltage divider resistors for the voltage channel is selected to ensure the mains voltage is divided down toadhere to the normal input ranges that are valid for the MSP430s SD24_B ADCs. Refer to theMSP4305xx/6xx user’s guide [3] and device specific datasheet [4] for these numbers.



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UnifiedClock

System

512KB256KB128KB

Flash

MCLK

ACLK

SMCLK

CPUXV2and

WorkingRegisters(25 MHz)

EEM(S: 8+2)

XIN XOUT

JTAG,SBW

Interface

Port PJ

eUSCI_A0eUSCI_A1eUSCI_A2eUSCI_A3

(UART,IrDA,SPI)

SD24_B

7 Channel6 Channel4 Channel

ADC10_A

10 Bit200 KSPS

LCD_C

8MUXUp to 320Segments

REF

Reference1.5 V, 2.0 V,

2.5 V

DVCC DVSS AVCC AVSS PA

I/O PortsP1, P2

2×8 I/OsInterrupt,Wakeup

PA1×16 I/Os

P1.x P2.xRST/NMI

32KB16KB

RAM

PJ.x

DMA

3 Channel

PMMAuxiliarySupplies

LDOSVM, SVS

BOR

MPY32

SYS

Watchdog

PortMapping

Controller

CRC16

PD

I/O PortsP7, P8

2×8 I/Os

PD1×16 I/Os

I/O PortsP9, P102×8 I/O

PE1×16 I/O

P7.x P8.x

PC

I/O PortsP5, P6

2×8 I/Os

PC1×16 I/Os

P5.x P6.x

PB

I/O PortsP3, P4

2×8 I/Os

PB1×16 I/Os

P3.x P4.x

eUSCI_B0eUSCI_B1

(SPI, I C)2

RTC_CE

(32 kHz)

AUX1 AUX2 AUX3

TA1TA2TA3

Timer_A2 CC

Registers

Ta0

Timer_A3 CC

Registers

COMP_B(ExternalVoltage

Monitoring)

I/O PortsP11

1×6 I/O

PF1×6 I/O

PF

P9.x P10.x

PE

P11.x

Block Diagram www.ti.com

Other signals of interest in Figure 1 are the PULSE LEDs (PULSE1 and PULSE2), which are used totransmit active and reactive energy pulses used for accuracy measurement and calibration. The pulsesare also used to transmit the active power consumed for each individual phase. In addition, the user canadd ZigBee communication to an in-home display by connecting a CC2530EM board into the RFconnectors of the design and flashing the CC2530 with the proper software.

2.1 Highlighted Products

2.1.1 MSP430F67791ASimilar to the MSP430F67791, the MSP430F67791A belongs to the powerful 16-bit MSP430F6xxplatform. This chip is intended for energy measurement applications and it has the necessary architectureto perform this application. The MSP430F67791A has a powerful 25-MHz CPU with MSP430CPUxarchitecture. The analog front-end consists of seven independent 24-bit ΣΔ analog-to-digital converters(ADC) based on a second order sigma-delta architecture that supports differential inputs. The sigma-deltaADCs (ΣΔ24_B) operate independently and are capable of 24-bit results. The sigma-delta ADCs can begrouped together for simultaneous sampling of voltages and currents on the same trigger. In addition, thesigma-delta ADC also has an integrated gain stage to support gains up to 128 for amplification of low-output current sensors. A 32-bit × 32-bit hardware multiplier on this chip can be used to further acceleratemath-intensive operations during energy computation.

Figure 2 shows a block diagram of the chip that displays the features of the MSP430F67791A.

Figure 2. MSP430F67791A Block Diagram

2.1.2 CC2530 FeaturesThe CC2530 device is a true system-on-chip (SoC) solution for IEEE 802.15.4, ZigBee, and RadioFrequency for Consumer Electronics (RF4CE) applications. The CC2530 enables robust network nodes tobe built with very-low bill-of-material costs. The CC2530 combines the excellent performance of a leadingRF transceiver with an industry-standard enhanced 8051 MCU, in-system programmable flash memory, 8-KB RAM, and many other powerful features. The CC2530 comes in four different flash versions:CC2530F32/64/128/256, with 32/64/128/256KB of flash memory, respectively. The CC2530 has variousoperating modes, making it highly suited for systems where ultra-low power consumption is required.Short transition times between operating modes further ensure low energy consumption. Combined withthe industry-leading and golden-unit-status ZigBee protocol stack (Z-Stack™) software from TexasInstruments, the CC2530F256 provides a robust and complete ZigBee solution.



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www.ti.com Block Diagram

2.1.3 TPS54060 FeaturesThe TPS5401 device is a 42-V, 0.5-A, step-down regulator with an integrated high-side MOSFET. Current-mode control provides simple external compensation and flexible component selection. A low-ripple pulse-skip mode reduces the supply current to 116 µA when outputting regulated voltage without a load. Usingthe enable pin, shutdown supply current reduces to 1.3 µA when the enable pin is low.

Undervoltage lockout is internally set at 2.5 V, but can be increased using the enable pin. The slow-startpin controls the output voltage start-up ramp. The output voltage start-up ramp is controlled by the slow-start pin that can also be configured for sequencing or tracking. In addition, an open-drain power-goodsignal indicates the output is within 94% to 107% of its nominal voltage



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0 10 20 30 40 50 60 70 80 90 100

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System Design Theory www.ti.com

3 System Design Theory

3.1 ESD IntroductionElectrostatic discharge (ESD) is a single-event rapid transfer of electrostatic charge between two objectsthat are at different voltages. ESD events can have a negative effect on electronic systems such ase-meters. There can be many sources for ESD. For an e-meter in particular, a charged person that is incontact with the meter (such as the operator of a meter) can potentially subject the meter to ESD.Depending on the humidity of the environment, and the material used to charge the charged person, thevoltage at which the person is charged varies. Figure 3 shows the electrostatic voltages in relation to thehumidity of the environment.

Figure 3. Maximum Values of Electrostatic Voltages People Can Be Charged to When in Contact WithDifferent Materials [1]

Because these devices are used in billing applications and should always remain functional, e-metersmust be designed with ESD immunity in consideration. The IEC 62052-11 standard accounts for thisconsideration by requiring all e-meters that adhere to this standard to pass ESD immunity tests accordingto IEC 61000-4-2.

The purpose of the IEC 61000-4-2 standard is to ensure that systems are tolerant of ESD exposure thatmay be present while a system is operating. The scope of the standard is to test electrical and electronicequipment that may be subjected to ESD from operators directly or from personnel to adjacent objects [1].Depending on the equipment and environment in which the equipment operates, the amount of ESDexposure can vary. The IEC 61000-4-2 defines multiple levels to cover the different types of exposurelevels. There are four standard levels; however, depending on special requirements, testing beyond these



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10% IP

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I30

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www.ti.com System Design Theory

conditions may be conducted. The level for testing is selected based on the purpose of the implementedsystem and the environment where the tests are to be deployed. For each test, a special unit (sometimesreferred to as an ESD gun), generates an ESD event that is meant to simulate the necessary ESDwaveform. Figure 4 shows an example of such an ESD waveform. Figure 5 shows this ESD gun, alongwith the entire setup for IEC 61000-4-2.

Figure 4. Ideal Contact Discharge Current Waveform at 4 kV (Taken from IEC 61000-4-2) [1]

Figure 5. ESD Test Bench for Powered Condition (Taken from IEC 61000-4-2) [1]



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47p

47p

15n

AGND

AGND

330k 330k 330k

2.3

7K

1k

1k

S20

K2

75

EXCML20A

EXCML20A

AGND

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C13

C12

R11 R12 R13

R19

R18

R34

R3

L5

L6

LINE3

NEUTRAL

V3+

V3-

P3+1

NEUTRAL

LINE3

V3


For e-meters, IEC 62052-11 specifically mentions that IEC 61000-4-2 should be conducted with contactdischarges (if applicable) of 8 kV and air discharges of 15 kV with ten discharge pulses at a rate of 1 Hz.However, based on different region requirements, sometimes a meter may have more stringentrequirements and must pass immunity testing at higher ESD voltage levels or larger number of dischargepulses.

3.2 Design Hardware Implementation

3.2.1 Analog InputsThe MSP430 analog front end consists of ΣΔ ADCs. Each converter is differential and requires that theinput voltages at the pins does not exceed ±930 mV (gain = 1) for optimum results. To meet this inputvoltage specification, the current and voltage inputs must be divided down. In addition, the SD24 allows amaximum negative voltage of −1 V; therefore, AC signals from mains can be directly interfaced without theneed for level shifters. This sub-section describes the analog front end used for voltage and currentchannels.

3.2.1.1 Voltage InputsThe voltage from the mains is usually 230 V or 120 V and is usually scaled down for optimal accuracywithin 930 mV. In the analog front end for voltage, there consists a spike protection varistor,electromagnetic interference (EMI) filter beads (which help for ESD testing), a voltage divider network, anda RC low-pass filter that functions as an anti-alias filter.

Figure 6. Analog Front End for Voltage Inputs

Figure 6 shows the analog front end for voltage inputs for a mains voltage of 230 V. The voltage isbrought down to approximately 549-mV RMS, which is 779 mV at the peak, and fed to the positive input.This voltage is within the MSP430ΣΔ analog limits by a safety margin greater than 15%. This marginallows accurate measurements even during voltage spike conditions. Additionally, it is important to notethat the anti-alias resistors on the positive and negative sides are different because the input impedanceto the positive terminal is much higher; therefore, a lower value resistor is used for the anti-alias filter. Ifthis is not maintained, a relatively large phase shift occurs.



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0

47p

47p

15n

AGND

AGND0

AVCC

13

1k

1k

SM

AJ5

.0C

A

AGNDPMLL4148PMLL4148

R/L9C16

C5

C17

R/L10

R2

1

R26

R27

D3

D11

D4

TV

S2

I1+

I1-

D28

D29D30

D31

D32D

12

I1+

I1-

AGND

CUR1+CUR1+

CUR1-CUR1-

I1


3.2.1.2 Current InputsThe analog front-end for current inputs is slightly different from the analog front end for the voltage inputs.Figure 7 shows the analog front end used for a current channel. The analog front end for current consistsof diodes and transorbs for transient voltage suppression. In addition, the front-end consists of EMI filterbeads (which help for ESD testing), burden resistors for current transformers, and also an RC low-passfilter that functions as an anti-alias filter.

Figure 7. Analog Front End for Current Inputs

As Figure 7 shows, resistor R21 is the burden resistor selected based on the current range used and theturns ratio specification of the CT (this design uses CTs with a turns ratio of 2000:1). The value of theburden resistor for this design is around 13 Ω. The antialiasing circuitry, consisting of resistors andcapacitors, follow the burden resistor. Based on this EVMs maximum current of 100 A, CT turns ratio of2000:1, and burden resistor of 13 Ω, the input signal to the converter is a fully differential input with avoltage swing of ±919 mV maximum when the maximum current rating of the meter (100 A) is applied. Inaddition, footprints for suppressant inductors are also available. Figure 7 shows these inductor footprintsas R/L9 and R/L10, which are populated by default with 0-Ω resistors.

3.2.2 Power SupplyThe MSP430 family of microcontrollers support a number of low-power modes in addition to low-powerconsumption during active (measurement) mode when the CPU and other peripherals are active. Becausean energy meter is always interfaced to the AC mains, deriving the DC supply required for the measuringelement (MSP430F67791A) is easily derived using an AC to DC conversion mechanism. The reducedpower requirements of this device family allow design of power supplies to be small, extremely simple andcost-effective. The power supply allows the operation of the energy meter by being powering it directlyfrom the mains. The next sub-sections discuss the various power supply options that are available tousers to support their design.



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150

uF

0.1

uF

SMAJ5.0ABCT

4.7u/400V

LL

NN

NCNC

2626

2222

VO+VO+

VO-VO-

C1

01

C4

2

ZD

3

C100

DGND

NEUTRAL

VCC_ISO

P3+1

+

2.2uF10

0u

F/1

00

V

0.22uF/305VAC

0.22uF/305VAC

Vsupply

1N4007

1N4007

1N4757A

1N4757A

0

0.22uF/305VAC1N4007

1N4757A

TPS54060_DGQ_10

1M

33

.2K 1M

0.01uF

0.1

uF

100

100

100

22

.1k

.056uF 100pF

NEUTRAL

NEUTRAL

NEUTRAL

B1

60

1mH

47uF

NEUTRAL

51

.13

1.6

k1

0k

NEUTRAL

C48

C1

02

C46

C50

D20

D22D21

D19

R39

C39D18

D17

U3

BOOT1

VIN2

EN3

SS/TR4

RT/CLK5 PWRGD 6VSENSE 7

COMP 8GND 9

PH 10

R3

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37

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C45

C4

7

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R93

R94

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C60 C61

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3

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C62

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6R

97

R9

8

VCC_PL

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P1+1

P2+1

P3+1

+


3.2.2.1 Resistor Capacitor (RC) Power SupplyFigure 8 shows a capacitor power supply that provides a single output voltage of 3.3 V directly from themains of 120-V to 230-V RMS AC at 50/60 Hz.

Figure 8. Simple Capacitive Power Supply for the MSP430 Energy Meter

The appropriate values of resistors (R92, R93, and R94) and capacitors (C39, C46, and C50) in Figure 8are chosen based on the required output current drive of the power supply. Voltage from mains is directlyfed to a RC based circuit followed by a rectification circuitry to provide a DC voltage for the operation ofthe MSP430 device. This DC voltage is regulated to 3.3 V for full-speed operation of the MSP430. Thedesign equations for the power supply are given in the application report Improved Load CurrentCapability for Cap-Drop Off-Line Power Supply for E-Meter [5].

The above configuration allows all three phases to contribute to the current drive, which is approximatelythree times the drive available from only one phase. If an even higher output drive is required, the samecircuitry can be used followed by an NPN output buffer. Another option is to replace the above circuitrywith a transformer/switching based power supply.

3.2.2.2 Switching-Based Power SupplyFigure 9 shows a switching-based power supply that provides a single output voltage of 3.3 V directly fromthe AC mains 100- to 230-V RMS. As the Figure 9 configuration shows, the meter is powered as long asthere is AC voltage on Phase C, corresponding to pad “LINE 3" on the hardware and P1/P3+1 on theschematic. The internal circuitry of a switching power supply is omitted from this application note. For thedrive of the power supply, refer to the documentation of the power supply module.

Figure 9. Switching-Based Power Supply for the MSP430 Energy Meter



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3.3 Metrology Software ImplementationThis section discusses the software for the implementation of three-phase metrology. The first subsectiondiscusses the setup of various peripherals of the MSP430. Subsequently, the the section describes theentire metrology software is described as two major processes: the foreground process and backgroundprocess.

3.3.1 Peripherals SetupThe major peripherals of the MSP430F67791A are the 24-bit sigma delta (ΣΔ24_B) ADC, clock system,timer, LCD, watchdog timer (WDT), and so forth.

3.3.1.1 ΣΔ24 SetupFor a three-phase system, at least six ΣΔs are necessary to independently measure three voltages andcurrents. The code accompanying this application note addresses the metrology for a three-phase systemwith limited discussion to anti-tampering; however, the code supports the measurement of the neutralcurrent. The clock to the ΣΔ24 (fM) is derived from system clock configured to run at 16 MHz. Thesampling frequency is defined as fs = fM / OSR; the OSR is chosen to be 256 and the modulationfrequency, fM, is chosen as 1.048576 MHz, resulting in a sampling frequency of 4096 samples per second.The ΣΔ24s are configured to generate regular interrupts every sampling instant.

The following are the ΣΔ channels associations:• A0.0+ and A0.0 → Voltage V1• A1.0+ and A1.0 → Voltage V2• A2.0+ and A2.0 → Voltage V3• A4.0+ and A4.0 → Current I1• A5.0+ and A5.0 → Current I2• A6.0+ and A6.0 → Current I3

Optional neutral channel can be processed via channel A3.0+ and A3.0–.

3.3.1.2 Real Time Clock (RTC_C)The RTC_C is a real-time clock module that is configured to give precise one second interrupts. Based offthese one second interrupts, the time and date are updated in software, as necessary.

3.3.1.3 LCD Controller (LCD_C)The LCD controller on the MSP430F67791A device can support up to 8-mux displays and 320 segments.The LCD controller is also equipped with an internal charge pump that can be used for good contrast. Inthe current design, the LCD controller is configured to work in 4-mux mode using 160 segments with arefresh rate set to ACLK/64, which is 512 Hz.

3.3.2 Foreground ProcessThe foreground process includes the initial setup of the MSP430 hardware and software immediately aftera device RESET. Figure 10 shows the flowchart for this process. The initialization routines involve thesetup of the ADC, clock system, general purpose input and output (GPIO) port pins, RTC module for clockfunctionality, LCD, and the USCI_A1 for universal asynchronous receiver and transmitter (UART)functionality. In addition, if ZigBee™ communication is enabled, USCI_A2 is configured.

After the hardware is setup, the foreground process waits for the background process to notify it tocalculate new metering parameters. This notification is done through a status flag every time a frame ofdata is available for processing. The data frame consists of the processed current, voltage, and active andreactive quantities that have been accumulated for one second. This accumulation is equivalent to theaccumulation of 50 or 60 cycles of data synchronized to the incoming voltage signal. In addition, a samplecounter keeps tracks of how many samples have been accumulated over this frame period. This countcan vary as the software synchronizes with the incoming mains frequency.



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Y

N

RESET

Hardware setup:Clock, SD24_B, port pins,

RTC_C, eUSCI, LCD, =LJ%HH��

Calculate RMS Current,RMS Voltage, Active Power,

Apparent Power, Reactive Power, Frequency (Hz), and Power Factor

Send active power reading to ZigBee Transmitter

LCD Display Management

1 second of Energy accumulated?

Wait for acknowledgement from Background

process


The data samples set consist of processed current, voltage, active and reactive energy. Processedvoltages accumulate in a 48-bit register. In contrast, processed currents, active energies, and reactiveenergies are accumulated in separate 64-bit registers to further process and obtain the RMS and meanvalues. Using the calculated values of active and reactive power from the foreground, the apparent poweris calculated. The frequency (in hertz) and power factor are also calculated using parameters calculatedby the background process using the formulas in Section 3.3.2.1.

Figure 10. Foreground Process



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3 3

ACT, Cumulative ACT,ph REACT, Cumulative REACT,ph

ph 1 ph 1

P P P P

= =

= =å å

Sample Samplecount count

ph 90 ph

2 2n 1 n 1ACT,ph ACT,ph REACT,ph REACT,ph APP,ph ACT,ph REACT,ph

v(n) i (n) v (n) i (n)

P K P K P P PSample count Sample count

= =

´ ´

= = = +

å å

Sample Samplecount count

ph ph ph ph

n 1 n 1RMS,ph v,ph RMS,ph i,ph

v (n) v (n) i (n) i (n)

V K I KSample count Sample count

= =

´ ´

= ´ = ´

å å


3.3.2.1 FormulaeThis section briefly describes the formulas used for the voltage, current, and energy calculations.

As described in the previous sections, voltage and current samples are obtained from the ΣΔ converters ata sampling rate of 4096 Hz. All of the samples that are taken in one second are kept and used to obtainthe RMS values for voltage and current for each phase. The RMS values are obtained by the followingformulas:

(1)

where• ph= Phase whose parameters are being calculated (i.e. Phase A (=1), B (=2), or C (=3)),• vph (n) = Voltage sample at a sample instant ‘n’,• iph (n) = Each current sample at a sample instant ‘n’,• Sample count = Number of samples in one second,• Kv,ph = Scaling factor for voltage,• Ki, ph = Scaling factor for each current. (2)

Power and energy are calculated for a frame’s worth of active and reactive energy samples. Thesesamples are phase corrected and passed on to the foreground process, which uses the number ofsamples (sample count) to calculate phase active and reactive powers via the following formulas:

where• v90 (n) = Voltage sample at a sample instant ‘n’ shifted by 90 degrees• KACT, ph= Scaling factor for active power• KREACT, ph= Scaling factor for reactive power (3)

In addition to calculating the per-phase active and reactive powers, the cumulative sum of theseparameters are also calculated by the below equations:

(4)

Please note that for reactive energy, the 90° phase shift approach is used for two reasons:1. It allows accurate measurement of the reactive power for very small currents2. It conforms to the measurement method specified by IEC and ANSI standards

The calculated mains frequency is used to calculate the 90 degrees-shifted voltage sample. Since thefrequency of the mains varies, it is important to first measure the mains frequency accurately in order tophase shift the voltage samples accordingly (refer to Section 3.3.3.3 Frequency measurement and cycletracking). The application’s phase shift implementation consists of an integer part and a fractional part.The integer part is realized by providing an N samples delay. The fractional part is realized by a fractionaldelay filter (refer to Section 3.3.3.2 Phase compensation).



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Act

Apparent

Act

Apparent

P, if capacitive load

P

P, if inductive load

P

Internal Representation of Power Factor-

ìï

= íïî

Sampling Rate (samples per second)Frequency (Hz)

Frequency (samples per cycle)=

3 3

ACT, Cumulative ACT,ph REACT, Cumulative REACT,ph

ph 1 ph-1

E E E E

=

= =å å

ACT, ph ACT, ph

REACT, ph REACT, ph

E P Sample count

E P Sample count

= ´

= ´


Using the calculated powers, energies are calculated by the following equations:

(5)

From there, the energies are also accumulated to calculate the cumulative energies, by the belowequations:

(6)

The background process calculates the frequency in terms of samples per Mains cycle. The foregroundprocess then converts this to Hertz by the following formula:

(7)

After the active power and apparent power have been calculated, the absolute value of the power factor iscalculated. In the meter’s internal representation of power factor, a positive power factor corresponds to acapacitive load and a negative power factor corresponds to an inductive load. The sign of the internalrepresentation of power factor is determined by whether the current leads or lags voltage, which isdetermined in the background process. Therefore, the internal representation of power factor is calculatedby the following formula:

(8)

3.3.3 Background ProcessThe background process uses the ΣΔ interrupt as a trigger to collect voltage and current samples (sevenvalues in total). These samples are used to calculate intermediate results. Since 16-bit voltage samplesare used, the voltage samples are further processed and accumulated in dedicated 48-bit registers. Incontrast, since 24-bit current samples are used, the current samples are processed and accumulated indedicated 64-bit registers. Active power and reactive power are also accumulated in 64-bit registers.

The background function deals mainly with timing critical events in software. Once sufficient samples(approximately one seconds worth) have been accumulated, then the foreground function is triggered tocalculate the final values of VRMS, IRMS, active, reactive and apparent powers, active, reactive and apparentenergy, frequency, and power factor. The background process is also wholly responsible for thecalculation of energy proportional pulses, frequency (in samples/cycle), and determining current lead/lagconditions. Figure 11 shows the flow diagram of the background process.



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Pulse generation in accordance to power

accumulation

Calculate frequency

Calculate power factor

Return from Interrupt

1 second of energy

calculated?

N

Y

Y

N

For each phase:

a. Remove residual DC

b. Accumulate for IRMS and VRMS

c. Accumulate samples for instantaneous Power

d. Calculate frequency in samples per cycle

e. Keep track of whether current lags or leads voltage

SD24_B Interrupts @

4096/sec

Read Voltages VA, VB, and VC

Read Currents IA, IB, IC

Store readings and notify foreground

process

All three phases done?


Figure 11. Background Process



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o oIN IN

DegS M

360 f 360 fDelay resolution

OSR f f

´ ´

= =

´

SD24OSRx = 32

Load SD24BPREx

with SD24PREx = 8


3.3.3.1 Voltage and Current SignalsThe ΣΔ Converter has fully differential input architecture and each ΣΔ pin can accept negative inputs;therefore, no level-shifting is necessary for the incoming AC voltage (unlike single-ended or pseudo-differential converters).

The output of each ΣΔ is a signed integer and any stray DC or offset value on these ΣΔs are removedusing a DC tracking filter. A separate DC estimate for all voltages and currents is obtained using the filter,voltage, and current samples respectively. This estimate is then subtracted from each voltage and currentsample.

The resulting instantaneous voltage and current samples are used to generate the following intermediateresults:• Accumulated squared values of voltages and currents, which is used for VRMS and IRMS calculations,

respectively• Accumulated energy samples to calculate active energy• Accumulated energy samples using current and 90° phase shifted voltage to calculate reactive energy

The foreground process processes these accumulated values.

3.3.3.2 Phase CompensationWhen a current transformer (CT) is used as a sensor, it introduces additional phase shift on the currentsignals. Also, the passive components of the voltage and current input circuit may introduce anotherphase shift. The user must compensate the relative phase shift between voltage and current samples toensure accurate measurements. The ΣΔ converters have programmable delay registers (ΣΔ24PREx) thatcan be applied to a particular channel. The use of this built-in feature (PRELOAD) is to provide therequired phase compensation. Figure 12 shows the usage of PRELOAD to delay sampling on a particularchannel.

Figure 12. Phase Compensation using PRELOAD Register

The fractional delay resolution is a function of input frequency (fIN), OSR, and the sampling frequency (fS).

(9)

In the current application, for an input frequency of 60 Hz, OSR of 256, and sampling frequency of 4096,the resolution for every bit in the preload register is about 0.02° with a maximum of 5.25° (maximum of255 steps).



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3.3.3.3 Frequency Measurement and Cycle TrackingThe instantaneous voltage is accumulated in a 48-bit register. In contrast, the instantaneous current,active power, and reactive power are accumulated in 64-bit registers. A cycle tracking counter and samplecounter keep track of the number of samples accumulated. When approximately one seconds worth ofsamples have been accumulated, the background process stores these accumulation registers andnotifies the foreground process to produce the average results, such as RMS and power values. Cycleboundaries are used to trigger the foreground averaging process because it produces very stable results.

For frequency measurements, a straight line interpolation is used between the zero crossing voltagesamples. Figure 13 shows the samples near a zero cross and the process of linear interpolation.

Figure 13. Frequency Measurement

Because noise spikes can also cause errors, the application uses a rate-of-change check to filter out thepossible erroneous signals and make sure that the two points are interpolated from genuine zero crossingpoints. For example, with two negative samples, a noise spike can make one of the samples positive,thereby making the negative and positive pair appear as if there is a zero crossing.

The resultant cycle-to-cycle timing goes through a weak, low-pass filter to further smooth out any cycle-to-cycle variations. This filtering results in a stable and accurate frequency measurement tolerant of noise.

3.3.3.4 LED Pulse GenerationIn electricity meters, the energy consumption of the load is normally measured in a fraction of kilowatt-hour (KWh) pulses. This information can be used to accurately calibrate any meter for accuracymeasurement. Typically, the measuring element (MSP430) is responsible for generating pulsesproportional to the energy consumed. Although, time jitters are not an indication of bad accuracy, timejitters give a negative indication of the overall accuracy of the meter. The jitter must be averaged out dueto this negative indication of accuracy.

This application uses average power to generate these energy pulses. The average power (calculated bythe foreground process) accumulates at every ΣΔ interrupt, thereby spreading the accumulated energyfrom the previous one-second time frame evenly for each interrupt in the current one-second time frame.This accumulation process is equivalent to converting power to energy. Once the accumulated energycrosses a threshold, a pulse is generated. The amount of energy above this threshold is kept and newenergy value is added on top of the threshold in the next interrupt cycle. Because the average powertends to be a stable value, this way of generating energy pulses is very steady and free of jitter.



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SD interrupts @ 4096 Hz

Energy Accumulator+= Average Power

Energy Accumulator > 1 tick?

Energy Accumulator = Energy Accumulator ±

1 tick

Generate 1 pulse

Proceed to other tasks

Y

N


The threshold determines the energy “tick” specified by meter manufacturers and is a constant. The “tick”is usually defined in pulses/kWh or just in KWh. One pulse must be generated for every energy “tick”. Forexample, in this application, the number of pulses generated/KWh is set to 6400 for active and reactiveenergies. The energy “tick” in this case is 1 KWh/6400. Energy pulses are generated and available on aheader and also through light-emitting diodes (LEDs) on the board. GPIO pins are used to produce thepulses. Figure 14 shows the flow diagram for pulse generation.

Figure 14. Pulse Generation for Energy Indication

The average power is in units of 0.01 W and a 1-KWh threshold is defined as:1-KWh threshold = 1 / 0.01 × 1 KW × (Number of interrupts/sec) × (Number of seconds in 1 hour) = 100000 ×4096 × 3600 = 0x15752A00000



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3.4 ESD Testing SoftwareWhen exposing equipment to ESD testing, failures can be classified into three categories:• Temporary loss of function or degradation of performance that ceases after the disturbance ceases.

The equipment under test recovers its normal performance without operator intervention. This is anacceptable failure for an e-meter in IEC 62052-11, assuming the energy readings were not affected byan amount greater than a certain threshold.

• Temporary loss of function or degradation of performance. Recovery requires operator intervention.• Temporary loss of function or degradation of performance that is not recoverable.

To better diagnose ESD failures from passes (and also distinguish the different failures into the threetypes of failures), a separate code example was loaded on the MSP430F67791A when performing ESDtesting. In this code example, the RST/NMI pin is configured to NMI mode. Additionally, whenever abrownout reset occurs, the red light of the EVM blinks three times before staying ON. Afterward, the greenLED of the EVM constantly blinks. If this green LED stops blinking, this indicates that the meter hastemporarily stopped working. If the red LED starts blinking again after previously being ON, then abrownout reset event has reoccurred.



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Isolated RS-232

JTAG

Capacitor Power Supply

RF Connector LEDS

IRDA TX/RX

160-Segment LCD

F6779

EEPROM

AUX

Voltage and Current Front End

Voltage and Current Inputs

Pulses

Pulses

Switch-Mode Power Supply

Getting Started www.ti.com

4 Getting Started

4.1 HardwareFor testing this design, the EVM430-F6779 is used and its MSP430F67791 is replaced with aMSP430F67791A. The following figures of the EVM best describe the hardware: Figure 15 is the top viewof the energy meter and Figure 16 then shows the location of various pieces of the EVM based onfunctionality.

Figure 15. Top View of the Three Phase Energy Meter EVM

Figure 16. Top View of the Three Phase Energy Meter EVM with Components Highlighted



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www.ti.com Getting Started

4.1.1 Connections to the Test Setup for AC VoltagesAC voltage or currents can be applied to the board for testing purposes at these points:• Pad “LINE1” corresponds to the line connection for phase A.• Pad “LINE2” corresponds to the line connection for phase B.• Pad “LINE3” corresponds to the line connection for phase C.• Pad “Neutral” corresponds to the Neutral voltage. The voltage between any of the three line

connections to the neutral connection must not exceed 230-V AC at 50/60 Hz.• I1+ and I1– are the current inputs after the sensors for phase A. When a current sensor is used, make

sure the voltages across I1+ and I1– does not exceed 930 mV. This is currently connected to a CT onthe EVM.

• I2+ and I2– are the current inputs after the sensors for phase B. When a current sensor is used, makesure the voltages across I2+ and I2– does not exceed 930 mV. This is currently connected to a CT onthe EVM.

• I3+ and I3– are the current inputs after the sensors for phase C. When a current sensor is used, makesure the voltages across I3+ and I3- does not exceed 930mV. This is currently connected to a CT onthe EVM.

• IN+ and IN– are the current inputs after the sensors for the neutral current. When a current sensor isused, make sure the voltages across IN+ and IN– does not exceed 930 mV. This is currently NOTconnected to a CT on the EVM.



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IC± VNIC+IB±IB+IA+ IA±

VA+ VB+ VC+ VN


Figure 17 and Figure 18 show the various connections that must be made to the test setup for properfunctionality of the EVM. When a test AC source must be connected, the connections have to be madeaccording to the EVM design. Figure 17 shows the connections from the top view. VA+, VB+, and VC+corresponds to the line voltage for phases A, B, and C, respectively. VN corresponds to the neutral voltagefrom the test AC source.

Figure 18 shows the connections from the front view. IA+ and IA– correspond to the current inputs for phaseA, IB+, and IB– correspond to the current inputs for phases B; IC+ and IC– correspond to the current inputs forphase C. VN corresponds to the neutral voltage from the test setup. Although the EVM hardware andsoftware supports measurement for the neutral current, the EVM obtained from Texas Instruments doesnot have a sensor connected to the neutral ADC channel.

Figure 17. Top View of the EVM With Test Setup Connections

Figure 18. Front View of the EVM With Test Setup Connections



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4.1.2 Power Supply Options and Jumper SettingsThe EVM can be configured to operate with different sources of power. The entire board can be poweredby a single DC voltage rail (DVCC), which can be derived either via JTAG, external power, or AC mainsthrough either the capacitive or switching power supplies. Various jumper headers and jumper settings arepresent to add to the flexibility to the board. Some of these headers require that jumpers be placedappropriately for the board to correctly function. Table 1 indicates the functionality of each jumper on theboard and the associated functionality.

Table 1. Header Names and Jumper Settings

HEADER AND MAINHEADER TYPE VALID USE-CASE COMMENTSFUNCTIONALITYOPTION NAMEThe software does not output ACLK by

ACLK (not default and will have to be modified to1-pin ACLK output Probe here to measure theisolated, do not output ACLK. This header is not isolatedheader (WARNING) frequency of ACLK.probe) from AC voltage so do not connect anymeasuring equipment.This header is not isolated from AC voltageProbe between here andACT (not isolated, 1-pin Active energy pulses so do not connect measuring equipmentsground for cumulative three-do not probe) header (WARNING) unless isolators external to the EVM arephase active energy pulses. available. See Isolated ACT instead.

Place a jumper here toconnect AUXVCC1 to GND.This jumper must be presentif AUXVCC1 is not used as abackup power supply.Alternatively, it can be used toprovide a back-up power

AUXVCC1 (not AUXVCC1 selection supply to the MSP430. To do2-pinisolated, do not and external power so, simply connect the --headerprobe) (WARNING) alternative power supply tothis header and configure thesoftware to use the backuppower supply as needed. Inaddition, on the bottom of theboard, a footprint is presentthat allows the addition of asuper capacitor.Place a jumper here to connect AUXVCC2 to GND. This jumper must beAUXVCC2 selectionAUXVCC2 (not 2-pin present if AUXVCC2 is not used as a backup power supply. Alternatively, itand AUXVCC2isolated, do not jumper/ can be used to provide a back-up power supply to the MSP430. To do so,external powerprobe) header simply connect the alternative power supply to this header and configure(WARNING) the software to use this backup power supply as needed.To power the RTC externallyregardless of whether DVCCis available, provide externalvoltage at AUXVCC3, disablethe internal AUXVCC3charger in software, and donot connect a jumper at thisheader. Alternatively, place ajumper at the “VDSYS” optionto connect AUXVCC3 to

AUXVCC3 (not 2-pin AUXVCC3 selection VDSYS so that it is poweredisolated, do not jumper/ and external power from whichever supply --probe) header (WARNING) (DVCC, AUXVCC1, or

AUXVCC2) is powering thechip. If this jumper is placed,disable the internal charger insoftware. To power the RTCexternally only when DVCC isnot available, enable theinternal charger, place ajumper at the “Diode”, optionand apply external voltage atthe VBAT header.

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Table 1. Header Names and Jumper Settings (continued)HEADER AND MAINHEADER TYPE VALID USE-CASE COMMENTSFUNCTIONALITYOPTION NAME

Not a jumper header, probehere for GND voltage. Do not probe if board is powered from ACDGND (not Ground voltage Connect negative terminal of mains, unless the AC mains are isolated.isolated, do not Header header (WARNING) bench or external power This voltage can be hot or neutral if ACprobe) supply when powering the wall plug is connected to the meter.board externally.Not a jumper header, probehere for VCC voltage.DVCC (not VCC voltage header Connect positive terminal of Do not probe if board is powered from ACisolated, do not Header (WARNING) bench or external power mains, unless the AC mains are isolated.probe) supply when powering theboard externally.

DVCCEXTERNAL (Do Place a jumper at this header This jumper option and the DVCCnot connect JTAG Jumper JTAG external power option to select external INTERNAL jumper option comprise oneif AC mains is the header selection pption voltage for JTAG three-pin header used to select the voltagepower source option (WARNING) programming. source for JTAG programming.Isolated JTAG orsupply is fine)DVCC INTERNAL Place a jumper at this header This jumper option and the DVCC(Do not connect Jumper JTAG internal power option to power the board EXTERNAL jumper option comprise oneJTAG if AC mains header selection Option using JTAG and to select the three-pin header used to select the voltageis the power option (WARNING) voltage from the USB FET for source for JTAG programming.source). JTAG programming.

Place a jumper only if AC mains voltage isneeded to power the DVCC rail. ThisPlace a jumper at this headerDVCC VCC_ISO Jumper header option and the DVCC VCC_PLSwitching-Mode position to power the boardISO (not isolated, header header option comprise one three-pinsupply select via AC mains using thedo not probe) option header that selects a capacitive powerswitching power supply. supply, a switching-mode power supply, orneither.Place a jumper only if AC mains voltage isneeded to power the DVCC rail. Do not

Place a jumper at this header debug using JTAG unless AC source isDVCC VCC_PL Jumper Capacitor power position to power the board isolated or JTAG is isolated. This header(not isolated, do header supply select via AC mains using the option and the DVCC VCC_ISO headernot probe) option (WARNING) capacitor power supply. option comprise one three-pin header thatselects a capacitive power supply, aswitching-mode power supply, or neither.

Not a jumper header, probe This header is Isolated from AC voltage so1-pin Isolated Active energy between here and ground for it is safe to connect to scope or otherISOLATED ACT header pulses cumulative three-phase active measuring equipment since isolators are

energy pulses. already present.Not a jumper header, probe This header is Isolated from AC voltage so

ISOLATED 1-pin Isolate reactive between here and ground for it is safe to connect to scope or otherREACT header energy pulses cumulative three-phase measuring equipment since isolators are

reactive energy pulses. already present.There are six headers that jumpers mustbe placed at to select a JTAGcommunication option. Each of these sixJ (Do not connect Place jumpers at the J headerJumper 4-wire JTAG headers has a J option and an S option toJTAG if AC mains options of all of the six JTAGheader programming option select either 4-wire JTAG or SBW. Tois the power communication headers tooption (WARNING) enable 4-wire JTAG, all of these headerssource) select 4-wire JTAG. must be configured for the J option. Toenable SBW, all of the headers must beconfigured for the S option.The software does not output MCLK byMCLK (not 1-pin MCLK output Probe here to measure the default and will have to be modified toisolated, do not header (WARNING) frequency of MCLK. output MCLK. Probe only when AC mainsprobe) is isolated

24 Three-Phase Metrology With Enhanced ESD Protection and Tamper Detection TIDU817–March 2015Submit Documentation Feedback


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Table 1. Header Names and Jumper Settings (continued)HEADER AND MAINHEADER TYPE VALID USE-CASE COMMENTSFUNCTIONALITYOPTION NAME

Not a jumper header, probe This header is not isolated from AC voltageREACT (not 1-pin Reactive energy between here and ground for so do not connect measuring equipmentsisolated, do not header pulses (WARNING) cumulative three-phase unless isolators external to the EVM areprobe) reactive energy pulses. available. See Isolated REACT instead.Probe here to measure the The software does not output RTCCLK by1-pin frequency of RTCCLK, whichRTCCLK RTCCLK output default and will have to be modified toheader is used for calibrating the output RTCCLK.RTC.Place a jumper here to enableJumper RS-232 receiveRX_EN receiving characters using --header enable RS-232.

There are six headers that jumpers mustbe placed at to select a JTAGcommunication. Each of these six headersS (Do not connect Place jumpers at the SJumper SBW JTAG that have a J option and an S option toJTAG if AC mains header options of all of the sixheader programming option select either 4-wire JTAG or SBW. Tois the power JTAG communicationoption (WARNING) enable 4-wire JTAG, all of these headerssource) headers to select SBW. must be configured for the J option. Toenable SBW, all of the headers must beconfigured for the S option.

1-pin I2C / EEPROM SCLSCL (not isolated, Probe here to probe I2C SCLjumper probe point Probe only when AC mains is isolateddo not probe) line.header (WARNING)1-pin I2C / EEPROM SDASDA (not isolated, Probe here to probe I2C SDAjumper probe point Probe only when AC mains is isolateddo not probe) line.header (WARNING)

The software does not output MCLK bySMCLK (not 1-pin SMCLK output Probe here to measure the default and will have to be modified toisolated, do not header (WARNING) frequency of SMCLK. output SMCLK. Probe only when AC mainsprobe) is isolatedJumper RS-232 transmit Place a jumper here to enableTX_EN --header enable RS-232 transmissions.

When the “Diode” option isAUXVCC3 external selected for AUXVCC3, apply2-pin power for AUXVCC3 voltage at this header so thatVBAT jumper --“Diode” option the RTC could still beheader (WARNING) powered when the voltage at

DVCC is removed.



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4.2 FirmwareThe source code is developed in the IAR environment using the IAR Embedded Workbench® IntegratedDevelopment Environment (IDE) Version 6.30.1 for the MSP430 IDE and Version 7.2.0.3640 for IARcommon components. Earlier versions of IAR cannot open the project files. When the project is loaded inIAR version 6.x or later, the IDE may prompt the user to create a backup. Click “YES” to proceed. Thereare three main parts to the energy metrology software:• The toolkit that contains a library of mostly mathematics routines• The metrology code that is used for calculating metrology parameters and application code that is used

for the host-processor functionality of the meter (that is communication, LCD display, RTC setup, andso forth)

• The GUI that is used for calibration

Figure 19 shows the contents of the source folder.

Figure 19. Source Folder Structure

The emeter-ng folder contains multiple project files and for this application, the emeter-6779A.ewp projectfile is to be used. The folder emeter-toolkit has corresponding project file emeter-toolkit-6779A.ewp. Forfirst time use, TI recommends completely rebuilding both of the projects by performing the following steps:1. Open the IAR IDE.2. Load the emeter_toolkit_6779A.ewp project.3. Click the Rebuild All option as shown in Figure 20.4. Close the existing workspace and open the main project emeter-6779A.ewp.5. Click Rebuild All (see Figure 21) and load this project onto the MSP430F67791A.



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Figure 20. Toolkit Compilation in IAR Figure 21. Metrology Project Build in IAR



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Test Setup www.ti.com

5 Test Setup

5.1 Metrology Test SetupFor performing metrology testing, a source generator was used to provide the voltage and current to themeter at the proper locations (see Section 4.1.1). The design tests used a nominal voltage of 230 V,calibration current of 10 A, and nominal frequency of 50 Hz. In the tests, current is varied from 50 mA to100 A. For each current, a phase shift of 0°, 60°, and −60° is applied between the voltage and current.

When voltage and current are applied to the meter, the meter outputs active energy pulses at a rate of6400 pulses/kWh. This pulse output feeds into a reference meter that determines the active energy %error (for the equipment used in this test, the reference meter was integrated in the same equipment usedfor the source generator). The active energy % error is based on the actual energy provided to the meterand the measured energy as determined by the active energy output pulse of the meter. Based on thisenergy pulse measurement, a plot of active energy % error versus current is created for 0°, 60, and -60°phase shifts as shown in Section 7.2.

5.2 ESD Test SetupWhen performing ESD testing, both a MSP430F67791-based meter and MSP430F67791A-based meterwere tested to show the ESD improvements of the MSP430F67791A. Both meters use the same board(EVM430-F6779). The only differences between the meters would be whether a MSP430F67791 orMSP430F67791A was actually populated on the boards. Although this test shows the comparativebehavior of the MSP430F67791 against the MSP430F67791A, please note that ESD testing for e-metersis a system-level test. Therefore, improvements from selecting the MSP430F67791A varies based onlayout and overall system design. Adhering to good ESD layout guidelines allows for maximum ESDimmunity. The presence of the MSP430F67791A cannot compensate for significant design weaknessesbecause the ESD testing is on a system level.

Each meter was tested by applying discharges on the coupling plane. The discharge was applied in thesame location for both meters. For each test point, ten strikes were applied. The tested ESD voltageswere 2 kV to kV in 2-kV increments with both positive and negative polarity.

To easily diagnose the state of the MSP430F67791A device when performing ESD testing, the EVM wasloaded with software performing the functions in Section 3.4. Using the software, the state of theMSP430F67791A can be determined from the EVM’s LEDs. In addition, the current drawn by themicrocontrollers were monitored to determine between latch-up or lock-up conditions.

Section 7.1 shows the results of these ESD tests.



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www.ti.com Viewing Metrology Readings and Calibration

6 Viewing Metrology Readings and CalibrationThe values of the metrology parameters can be viewed on the LCD or the GUI. In addition, the activepower reading can be viewed from an in-home display that communicates with the meter through ZigBee.

6.1 Viewing Results Through LCDThe LCD display scrolls between metering parameters approximately every two seconds. For eachmetering parameter that shows on the LCD, three items are actually displayed on the screen: thecorresponding phase of the parameter, a 1 or 2 character symbol, which is used to distinguish theparameter being displayed and the actual value of that parameter. The phase of the parameter displayson the top line of the LCD. This may take the values of A, B, C, and t for phase A, phase B, phase C, andthe aggregate-sum of these phases, respectively. The parameter symbol shows on the left side of thesecond line of the LCD. The actual value of the parameter shows just to the right of the parameter symbol.Table 2 shows the different metering parameters that are displayed on the LCD and the associated unitsin which they are displayed. The SYMBOL column in Table 2 shows which characters correspond to whichmetering parameter. The COMMENTS column of Table 2 provides a brief interpretation of the displayedmetering parameters.

Table 2. Displayed Parameters

PARAMETER NAME SYMBOL UNITS COMMENTS

Voltage Volts (V) --

Current Amps (A) --

Active power Watt (W) --

Reactive power Volt-ampere reactive (var) --

Apparent power Volt-ampere (VA) --



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Symbol Value Phase

Viewing Metrology Readings and Calibration www.ti.com

Table 2. Displayed Parameters (continued)PARAMETER NAME SYMBOL UNITS COMMENTS

Frequency Hertz (Hz) --

The characters

are used if the load isdetermined to be a capacitive

load. The charactersPower factor or Constant between 0 and 1

are used if the load isdetermined to be an inductive

load.

Every 10 ticks increments theTotal consumed active energy 100 “ticks” tenths place by 1.

Total consumed reactive Every 10 ticks increments the100 “ticks”energy tenths place by 1.

Figure 22 shows an example of phase A’s measured frequency of 49.99 Hz being displayed on the LCD.

Figure 22. LCD Display



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6.2 Viewing Results Using RF Technology (ZigBee)The CC2530 Evaluation Module (EM) is an add-on and plug-in daughter card for ZigBee and IEEE802.15.4 radio frequency (RF) applications in the 2.4-GHz, unlicensed industrial, scientific, and medical(ISM) band (see Figure 23). The communication interface to any host/application processor is throughUART. The instantaneous power consumption sends periodically to the ZigBee module for wirelesstransmission.

Figure 23. ZigBee Radio

This ZigBee module connects through the UART, which is configured to 115.2 kbaud on the transmitportion of the MSP430F67791A and the receive portion of the MSP430F4618 (IHD430).

6.2.1 In-Home DisplayMost IHDs have their own setup mechanism and all of them tend to join the ZigBee network when turnedON. This section describes the in-home display using TI’s IHD430 (TIDM-LOWEND-IHD), which Figure 24shows. The IHD430 has an MSP430F461x device as an application/host processor.

Figure 24. TIDM-LOWEND-IHD



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Viewing active power readings on the IHD430Place a CC2530 module in the RF connector socket of the meter EVM430-F6779, making sure that themodule is properly oriented. This CC2530 is flashed with code to act as a transmitter. The IHD430 alsohas a corresponding CC2530 module that has been flashed to act as a receiver.

Initializing the IHD430Power must be provided by 2 AAA batteries or an external supply. The power source is selected byconfiguring jumpers on the VCC and BATT headers and the power is supplied to the on-board MSP430 byplacing a jumper on the PWR1 header. The power setup options are provided in the following list.1. Jumper settings to provide battery power are:

(a) Place jumper on BATT header(b) Place jumper on PWR1 header

2. Jumper settings to provide flash emulation tool power are:(a) Place jumper on pins [1-2] on VCC 3-pin header(b) Place jumper on PWR1 header

3. Jumper settings to provide external power are:(a) Place jumper on pins [2-3] on VCC 3-pin header(b) Place jumper on PWR1 header

4. Ensure jumper is placed on RF_PWR header, which has been provided to enable and disable power toCC2530

The “IHD430_SUPPORT” macro must be defined in the emeter-3ph-neutral-6779(A).h file for theMSP430F67791A software to communicate the active power to the IHD430. When this macro is enabled,the active power reading sends to the on-board CC2530 transmitter through 8N1 UART communication ata baud rate of 115.2 k. The CC2530 then sends the data to the CC2530 receiver. The IHD430 receivesthe active power readings and displays it on the LCD. Please note, the transmitter (meter) must be turnedON before the receiver to ensure proper ZigBee communication. In addition, modifications can be made tothe MSP430F67791A software to send different parameters for display onto the IHD430.



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6.3 Calibrating and Viewing Results Through PC

6.3.1 Viewing ResultsTo view the metrology parameter values through the GUI, utilize the following steps:1. Connect the EVM to a PC through an RS-232 cable.2. Open “GUI” folder and open calibration-config.xml in a text editor.3. Change the "port name" field within the "meter" tag to the COM port connected to the meter. In

Figure 25, this field shows COM2.

Figure 25. GUI Config File Changed to Communicate With Meter

4. Run calibrator.exe, which is located in the GUI folder. If the COM port in calibration-config.xml hasbeen changed in the previous step to the COM port connected to the EVM, the GUI opens (seeFigure 26). If the GUI connects properly to the EVM, the top left button is green. The button is red ifthere are problems with connections or if the code is not configured correctly. Click the green button toview the results.

Figure 26. GUI Startup Window



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Upon clicking on the green button, the results window opens (see Figure 27). In Figure 27, there is atrailing "L" or "C" on the "Power factor" values to indicate an inductive or capacitive load, respectively.

Figure 27. GUI Results Window

From the GUI results window, the user can either view the meter settings by clicking the“Meter features”button, view the meter calibration factors by clicking the “Meter calibration factors” button, or open thewindow used for calibrating the meter by clicking the “Manual cal.” button.



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6.3.2 CalibrationCalibration is key to the performance of any meter and is an absolutely necessary process for every meterto undergo. Initially, every meter exhibits different accuracies due to silicon-to-silicon differences, sensoraccuracies, and other passive tolerances. To nullify the effects of the aforementioned variables, everymeter must be calibrated. For calibration to be performed accurately there should be an accurate AC testsource and a reference meter available. The source must be able to generate any desired voltage,current, and phase shifts (between V and I). To calculate errors in measurement, the reference meter actsas an interface between the source and the meter being calibrated. This section discusses a simple andeffective method of calibration of this three-phase EVM.

The GUI used for viewing results can easily be used to calibrate the EVM. Parameters called calibrationfactors are modified in the software during the calibration to give the least error in measurement. For thismeter, there are four main calibration factors for each phase: voltage scaling factor, current scaling factor,power scaling factor, and the phase compensation factor. The voltage, current, and power scaling factorstranslate measured quantities in metrology software to real world values represented in volts, current, andwatts respectively. The phase compensation factor is used to compensate any phase shifts introduced bythe current sensors and other passives.

When the meter software is flashed with the code (available in the *.zip file), default calibration factors areloaded into these calibration factors. The GUI modifies these values during calibration. The calibrationfactors are stored in INFO_MEM and they remain the same if the meter is restarted. However, if code isre-flashed during debugging operations, the calibration factors are replaced and the meter must berecalibrated. One way to save the calibration values is by clicking on the “Meter calibration factors” button(Figure 27). The meter calibration factors window Figure 28) shows the latest values. This informationcould be used to directly replace the macro definition of these factors in the source code.

Figure 28. Calibration Factors Window

Calibrating any of the scaling factors is referred to as gain correction. Calibrating the phase compensationfactors is referred to as phase correction. For the entire calibration process, the AC test source must beON, meter connections consistent with Section 4.1.1, and the energy pulses must be connected to thereference meter.

6.3.2.1 Gain CalibrationUsually gain correction for voltage and current can be done simultaneously for all phases. However,energy accuracy (%) from the reference meter for each individual phase is required for gain correction ofactive power parameters. Also, when performing active power calibration for any given phase, the othertwo phases must be turned OFF. Typically just switching the currents OFF is sufficient for disabling aphase.



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6.3.2.1.1 Voltage and Current Gain CalibrationTo calibrate the voltage and current readings, utilize the following steps:1. Connect the GUI to view results for voltage, current, active power, and the other metering parameters.2. Configure the test source to supply desired voltage and current for all phases. Ensure that these are

the voltage and current calibration points with a zero-degree phase shift between the voltage andcurrent (for example 230 V, 10 A, 0º (PF = 1). Typically, these values are the same for every phase.

3. Click on “Manual cal.” button (see Figure 27). The following screen pops up on the display Figure 29:

Figure 29. Manual Calibration Window

4. Calculate the correction values for each voltage and current. The correction values that must beentered for the voltage and current fields are calculated by:

where• valueobserved, is the value measured by the TI meter,• valuedesired is the calibration point configured in the AC test source. (10)

5. After calculating for all voltages and currents, input these values as is (±) for the fields “Voltage” and“Current (low)” for the corresponding phases.

6. Click on “Update meter” and the observed values for the voltages and currents on the GUI updategradually to the desired voltages and currents.

6.3.2.1.2 Active Power Gain CalibrationAfter performing gain correction for voltage and current, gain correction for active power must be done.Gain correction for active power is done differently in comparison to voltage and current. Although,conceptually, calculating using Step 4 with Active power readings (displayed on the AC test source) canbe done, it is not the most accurate method and should be avoided.

The best option to get the Correction(%) is directly from the reference meters measurement error of theactive power. This error is obtained by feeding energy pulses to the reference meter. To perform activepower calibration, utilize the following steps:1. Turn off the meter and connect the meters energy pulse output to the reference meter. Configure the

reference meter to measure the active power error based on these pulse inputs.2. Turn on the AC test source.3. Repeat Steps 1 to 3 from the previous Section 6.3.2.1.1 with the identical voltages, currents, and 0º

phase shift that were used in the previous section.4. Obtain the % error in measurement from the reference meter. Note that this value may be negative.



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5. Enter the error obtained in the above step into the “Active (low)” field under the corresponding phase inthe GUI window. This error is already the value and does not need to be calculated.

6. Click on “Update meter” and the error values on the reference meter would immediately settle to avalue close to zero.

6.3.2.2 Phase CorrectionAfter performing power gain correction, phase calibration must be performed. Similar to active power gaincalibration, to perform phase correction on one phase, the other phases must be disabled. To performphase correction calibration, perform the following steps:1. If the AC test source has been turned OFF or reconfigured, perform steps 1-3 from the voltage and

current gain section using the identical voltages and currents used in that section.2. Disable all other phases that are not currently being calibrated by setting the current of these phases to

0 A.3. Modify only the phase-shift to a non-zero value; typically, +60º is chosen. The reference meter now

displays a different % error for active power measurement. Note that this value may be negative.4. If this error is not close to zero, or is unacceptable, perform phase correction by following these steps:

(a) Enter a value as an update for “Phase (Low)” field . Usually, a small ± integer should be entered tobring the error closer to zero. Additionally, for a phase shift greater than 0 (for example: +60º), apositive (negative) error would require a positive (negative) number as correction.

(b) Click on “Update meter” and monitor the error values on the reference meter.(c) If this measurement error (%) is not accurate enough, fine tune by incrementing/decrementing by a

value of one based on the previous Steps 4a and 4b. Please note, after a point, the fine-tuning onlyresults in the error oscillating on either side of zero. The value that has the smallest absolute errormust be selected.

(d) Change the phase now to –60° and check if this error is still acceptable. Ideally, errors must besymmetric for same phase shift on lag and lead conditions.

After performing phase correction, calibration is complete for one phase. Please note that the gaincalibration and phase calibration are completed in sequence for each phase before moving on to otherphases. These two procedures must be repeated for each phase unlike voltage and current calibration.

This completes calibration of voltage, current and power for all three phases. The new calibration factorsas shown in Figure 30 can be viewed by clicking the “Meter Calibration factors” button of the GUI meteringresults window in Figure 27.

Figure 30. Calibration Factors Window



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The configuration of the meter can be viewed by clicking on the “Meter features” button to access screenthat Figure 31 shows.

Figure 31. Meter Features Window



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www.ti.com Test Data

7 Test Data

7.1 ESD ResultsTo test the comparative ESD robustness between the MSP430F67791A and MSP430F67791, an IEC61000-4-2 test was performed on one EVM430-F6779 that had the MSP430F67791A as the metering SoCand another EVM430-F6779 that had the non-A MSP430F67791 as the metering SoC. Please note thatfor the EVM430-F6779, some ESD tradeoffs were made to fully support showcasing the features of thesilicon and ease-of-use for evaluation purposes. However, the EVM can still be used as a gauge to showthe improvements in using the MSP430F67791A devices instead of the MSP430F67791.

For applying the ESD test on the two test EVMs, both positive and negative polarity discharges wereapplied on both test boards at the same location. In the tests, recoverable failures (a reset, for example),lock-ups, and latch-ups were logged as failures. Table 3 shows the results of these tests. In these tests,voltage levels where both positive and negative polarity tests passed are colored green, tests where onlyeither positive or negative polarity tests passed are colored yellow, and tests where both positive andnegative polarity tests failed are colored red.

Table 3. 2 IEC 61000-4-2 Test Results for MSP430F67791 and MSP430F67791A

TEST VOLTAGE F67791 RESULTS (+POLARITY/ –POLARITY) F67791A RESULTS (+POLARITY/ –POLARITY)1 kV Pass/Pass2 kV Pass/Pass Pass/Pass4 kV Pass/Pass Pass/Pass6 kV Pass/Pass Pass/Pass8 kV Pass/Pass Pass/Pass10 kV Fail/Pass Pass/Pass12 kV Fail/Fail Pass/Pass14 kV Pass/Pass16 kV Pass/Pass18 kV Pass/Pass20 kV Pass/Pass

From these results, there is a clear improvement in selecting the MSP430F67791A devices over theMSP430F67791. The MSP430F67791A chips pass up to 20 kV at the location tested, which is animprovement by 8 kV to 10 kV.



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Test Data www.ti.com

7.2 Metrology Result ComparisonRegardless of the improvements made in the MSP430F67791A, metrology performance is still comparableto the non-A MSP430F67791. To show this, an EVM430-F67791 was tested with a MSP430F67791 and aMSP430F67791A. The results for these tests are in Table 4, Figure 32, and Figure 33. These results showthat the MSP430F67791A can still meet the class 0.2% accuracy requirements fulfilled by the non-AMSP430F67791.

Table 4. Active Energy % Error for MSP430F67791 and MSP430F67791A

MSP430F67791 MSP430F67791ACURRENT 0° 60° –60° 0° 60° –60°(Amps)

0.05 –0.043 –0.086 –0.076 –0.011 –0.024 –0.080.1 –0.053 –0.019 –0.068 –0.005 0.077 –0.0790.25 –0.028 –0.03 –0.057 –0.018 0.005 –0.0780.5 –0.014 –0.018 –0.04 –0.027 –0.009 –0.0581 –0.01 –0.004 –0.022 –0.015 0 –0.042 –0.0206667 –0.00166667 –0.039 –0.029 0.00166667 –0.05433335 –0.018 –0.015 –0.0123333 –0.0216667 –0.0113333 –0.029666710 –0.00733333 –0.0233333 0.0143333 –0.0126667 –0.017 –0.0083333320 –0.00833333 –0.042 0.028 –0.010667 –0.0273333 0.0066666730 –0.000333333 –0.0646667 0.062 –0.005 –0.043 0.039333340 –0.003 –0.091 0.078 –0.00233333 –0.0606667 0.056333350 –0.0143333 –0.122 0.0983333 –0.008 –0.101333 0.078666760 –0.009 –0.135 0.11333 –0.0106667 –0.113333 0.086333370 –0.0123333 –0.148667 0.12 –0.0113333 –0.120667 0.096333380 –0.011 –0.15 0.130333 –0.016 –0.131667 0.09790 –0.014 –0.158667 0.126333 –0.018 –0.136 0.098100 –0.027 –0.179333 0.119333 –0.0253333 –0.144333 0.0933333



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www.ti.com Test Data

Figure 32. EVM430-F6779 Performance With MSP430F67791

Figure 33. EVM430-F6779 Performance With MSP430F67791A



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Clock Headers

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MSP430F67791A

MSP430F67791AIPEU

Design Files www.ti.com

8 Design Files

8.1 SchematicsTo download the Schematics for each board, see the design files at http://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.

Figure 34. TIDM-3PHMTR-TAMP-ESD Schematic Page 1



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Analog Front-End (Voltage)Analog Front-End (Current)

0

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47p

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15n

15n

15n

15n

AGND

AGND

AGND

AGND

AGND

AGND

AGND

AGND

0

0

AVCC

330k 330k 330k

2.3

7K

1k

330k 330k 330k

2.3

7K

1k

1k

12.4

12.4

1k

1k

1k

1k

1k

S20

K2

75

S20

K2

75

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

EXCML20A

EXCML20AS

MA

J5

.0C

AS

MA

J5

.0C

A

0

47p

47p

15n

AGND

AGND

0

12.4

1k

1k

PMLL4148

PMLL4148

PMLL4148

PMLL4148

SM

AJ5

.0C

A

47p

47p

15n

AGND

AGND

330k 330k 330k

2.3

7K

1k

1k

S20

K2

75

EXCML20A

EXCML20A

0

47p

47p

15n

AGND

AGND

AGND

0

12.4

1k

1k

PMLL4148

PMLL4148

PMLL4148

PMLL4148

SM

AJ5

.0C

A

AGND

AGND

AGND

AGND

AGND

AGND

AGND

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

PMLL4148

R/L9

R/L11

C2

C11

C16

C5

C18

C6

C1

C9

C8

C10

C17

C19

R/L10

R/L12

R5 R6 R7

R15

R14

R8 R9 R10

R17

R16

R32

R22

R21

R28

R26

R33

R27

R29

R1

R2

D3

D11

D4

D5

D13

D6

D14

L1

L3T

VS

2T

VS

3

R/L13C20

C7

C21

R/L14

R23

R30

R31

D7

D15

D8

D16

TV

S4

C3

C13

C12

R11 R12 R13

R19

R18

R34

R3

L5

L6

R/L7C14

C4

C15

R/L8

R20

R24

R25

D1

D9

D2

D10

TV

S1

LINE1

LINE2

LINE3

NEUTRAL

I1+

I1-

I2+

I2-

I3+

I3-

IN+

IN-

D28

D29D30

D31

D32

D33

D34

D35

D36

D37

D38

D39

D40

D41

D42

D43

D12

V1+P1+1

I2+

I1+

I2-

I1-

V1-

V2+

V2-

P2+1

AGND

AGND

AGND

I3+

I3-

V3+

V3-

P3+1

IN+

IN-

NEUTRAL

NEUTRAL

NEUTRAL

LINE1

LINE2

LINE3

CUR1+CUR1+

CUR1-CUR1-

CUR2+

CUR2-

CUR3+

CUR3-

CURN+

CURN-

V2

I1

I2

V1

I3

V3

IN

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DVCC

2.2uF100

uF

/10

0V

0.22uF/305VAC

0.22uF/305VAC

Vsupply

1N4007

1N4007

1N4757A

1N4757A

0

0.22uF/305VAC1N4007

1N4757A

150

uF

0.1

uF

SMAJ5.0ABCT

4.7u/400V

TPS54060_DGQ_10

1M

33.2

K 1M

0.01uF

0.1

uF

100

100

100

22.1

k

.056uF 100pF

NEUTRAL

NEUTRAL

NEUTRAL

B16

0

1mH

47uF

NEUTRAL

51.1

31.6

k1

0k

NEUTRAL

C48

C1

02

C46

C50

D20

D22D21

D19

R39

C39D18

D17

LL

NN

NCNC

26 26

22 22

VO+ VO+

VO- VO-

C1

01

C4

2

ZD

3

C100

JP

3

123

U3

BOOT1

VIN2

EN3

SS/TR4

RT/CLK5 PWRGD 6VSENSE 7

COMP 8GND 9

PH 10

R35

R37

R38

C45

C4

7

R92

R93

R94

R9

5

C60 C61

D23

L7

C62

R96

R97

R98

VCC_PL

VCC_PL

DGND

DGND

NEUTRAL

NEUTRAL

VCC_ISO

VCC_ISO

P1+1

P2+1

P3+1

P3+1+

+

VCC Select

Un-isolated VCC from AC Mains

Isolated VCC from AC Mains





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RF Daughter Card

IR Pulse In/OutIsolated RS232 Communication

EZ-RF Connect

Act / React

EEPROM

DGND

DGND

DGND

PS8802

PS8802

SL127L6TH

1kTIL191

VCC

10u

F

0.1

uF

DGND

1kTIL191

VCC

DGND

DVCC

0000

00000000

0

00

DVCC

DVCC

47

DGND

0.1uF

4.7uF

DGND DGND

2.2k

68

DVCC

DNP

1.5k

1k

10k

220

BC857BSMD

BC857BSMD

0.1

uF

LL103A

10uF

10uF

LL103A

LL103A

LL1

03

A1

k

2.2k

DN

P

0.1uF

DGNDDGND

24C02CSN

0.1

uF

DVCC

DGND

DGND

DGND

000

RS-232

162738495

G1

G2

U12

3

78

5

6

U22

3

78

5

6

RX

_E

N

12

TX

_E

N

12

RF2RF2

1 23 45 67 89 10

11 1213 1415 1617 1819 20

RF1RF1

1 23 45 67 89 10

11 1213 1415 1617 1819 20

EZ-RF

21

43

56

R68

OPTO11

2 3

4

C5

8

C5

9

JP1112

R72

OPTO21

2 3

4

JP1212

R74R76R80R82

R75R81R83R84R85R86R88R91

R87

R90R89

GND

RXDSD

TXD

VCC1

VCC2

R4

7

C52

C51

R69

R65R66

R67

R62

R6

3

R6

4Q2

Q1

C5

4

D24

C56

C55

D26

D25

D2

7R

78

R71

R70

C57

VCC

GND

IC1 84

SCL6

SDA 5

A01A12A23

WP7

C4

1

R79R77R73

ACT

12

REACT

12

RF_FIFORF_FIFO

RF_FIFOPRF_FIFOP

RF_SFDRF_CCA

RF_SOMIRF_SIMORF_CLKRF_CS

UART_TX

DVCC

DVCC

DVCC

DGND

RF_GPIO2

ACTIR_SD

IR_RXDIR_TXD

REACT

DB9_-12V

DB9_GND

DB9_+12V

UART_RXRS232_RXD

RS232_TXD

EZ-RF_TXD

EZ-RF_RXD

SCL

SDA

RF_RESETCC

RF_RESETCC

RF_VREG_EN

RF_GPIO1

IRDA

Arr

ay

EE

PR

OM





http://www.ti.com



8.2 Bill of MaterialsTo download the Bill of Materials for each board, see the design files at http://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.

8.3 PCB Layout RecommendationsPCB layout is an important factor in a meters ESD immunity performance. The EVM430-F6779 inparticular was designed to make it easy to evaluate the MSP430F67791 as an e-meter SoC. As a result,in certain instances, ESD performance was traded off for ease of evaluation of the EVM. However, ingeneral, some PCB layout guidelines for ESD performance are the following:• Use ground planes instead of ground traces where possible and minimize the cuts in these ground

planes(especially for critical traces) in the direction of current flow. Ground planes provide a low-impedance ground path which minimizes induced ground noise. However, cuts in the ground plane canincrease inductance. If there are cuts in the ground plane, they should be bridged on the opposite sidewith a 0-Ω resistor.

• When there is a ground plane on both top and bottom layers of a board (such as in the EVM of thisdesign) ensure there is good stitching between these planes through the liberal use of vias thatconnect the two planes.

• Keep traces short and wide to reduce trace inductance. If an LCD is used, place it near themicrocontroller and prevent long LCD traces to the microcontroller.

• Use wide VCC traces and star-routing for these traces instead of point-to-point routing.• Minimize the length of the microcontrollers reset trace and other critical edge-triggered traces.• Isolate sensitive circuitry from noisy circuitry. For example, high voltage and low voltage circuitry must

be separated.• Use transient voltage suppressors, EMI suppressant ferrite beads, and other ESD protection devices to

suppress the effects from an ESD discharge. The turn on time of these devices should be small sincethe rise time of ESD discharge waveform is also small. ESD protection devices can be found at thefollowing link: www.ti.com/esd.

• Keep sensitive circuitry away from PCB edges. If a ground plane is present, put sensitive circuitry nearthe center of these ground planes.

• Use decoupling capacitors with low effective series resistance (ESR) and effective series Inductance.Place decoupling capacitors close to their associated pins.

• Place connectors all on one edge of the PCB, especially through-hole connectors since they causebreaks in the ground plane.

• Minimize the length of the traces used to connect the crystal to the microcontroller. Place guard ringsaround the leads of the crystal and ground the crystal housing. In addition, there should be cleanground underneath the crystal and placing any traces underneath the crystal should be prevented.Also, keep high frequency signals away from the crystal.

For more ESD recommendations please refer to SLAA530 [6].

8.4 Layer PlotsTo download the layer plots, see the design files at http://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.

8.5 CAD ProjectTo download the CAD project files, see the design files at http://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.

8.6 Gerber FilesTo download the Gerber files for each board, see the design files at http://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.



http://www.ti.com



https://www.ti.com/esd








8.7 Software FilesTo download the software files for this reference design, please see the software athttp://www.ti.com/tool/TIDM-3PHMTR-TAMP-ESD.

9 References

1. International Electrotechnical Commission, IEC 61000-4-2, Electromagnetic capability (EMC)—Part 4:Testing and measurement techniques – Electrostatic discharge immunity test, Ed. 2.0.

2. Texas Instruments, Segment LCD-Based Low-End In-Home Display with Wireless RF Communication,User's Guide, (TIDU203).

3. Texas Instruments, MSP430x5xx and MSP430x6xx Family, User's Guide, (SLAU208).4. Texas Instruments, MSP430F677x1A, MSP430F676x1A, MSP430F674x1A Polyphase Metering SoCs,

Data Sheet, (SLAS983).5. Texas Instruments, Improved Load Current Capability for Cap-Drop Off-Line Power Supply for E-Meter,

Application Report, (SLVA491).6. Texas Instruments, MSP430 ™ System-Level ESD Considerations, Application Report, (SLAA530).

10 About the AuthorMEKRE MESGANAW is a Systems Engineer in the Smart Grid and Energy group at Texas Instruments,where he primarily works on electricity metering customer support and reference design development.Mekre received his Bachelor of Science and Master of Science in Computer Engineering from the GeorgiaInstitute of Technology.



http://www.ti.com


http://www.ti.com/lit/pdf/TIDU203

http://www.ti.com/lit/pdf/SLAU208

http://www.ti.com/lit/pdf/SLAS983

http://www.ti.com/lit/pdf/SLVA491

http://www.ti.com/lit/pdf/SLAA530


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