ANALOG DEVICES ADE7761 Service Manual

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Energy Metering IC with On-Chip

FEATURES

High accuracy active energy measurement IC, supports

IEC 687/61036 Less than 0.1% error over a dynamic range of 500 to 1 Supplies active power on the frequency outputs F1 and F2 High frequency output CF is intended for calibration and

supplies instantaneous active power Continuous monitoring of the phase and neutral current

allows fault detection in 2-wire distribution systems Current channels input level best suited for current

transformer sensors Uses the larger of the two currents (phase or neutral) to

bill—even during a fault condition Continuous monitoring of the voltage and current inputs

allows missing neutral detection Uses one current input (phase or neutral) to bill when

missing neutral is detected Two logic outputs (FAULT and REVP) can be used to indicate

a potential miswiring, fault, or missing neutral condition Direct drive for electromechanical counters and 2-phase

stepper motors (F1 and F2) Proprietary ADCs and DSP provide high accuracy over large

variations in environmental conditions and time Reference 2.5 V ± 8% (drift 30 ppm/°C typical) with external

overdrive capability Single 5 V supply, low power

FUNCTIONAL BLOCK DIAGRAM

AGND FAULT

MISCA

6 5

2.5V

REFERENCE

4kΩ

ADC

A>B

B>A

A<>B

MISSING NEUTRAL

INTERNAL

OSCILLATOR

HPF

GAIN ADJUST

Fault and Missing Neutral Detection

ADE7761

GENERAL DESCRIPTION

The ADE7761 is a high accuracy, fault tolerant, electrical energy measurement IC intended for use with 2-wire distribution systems. The part specifications surpass the accuracy requirements as quoted in the IEC61036 standard.

The only analog circuitry used on the ADE7761 is in the ADCs and reference circuit. All other signal processing (such as multiplication and filtering) is carried out in the digital domain. This approach provides superior stability and accuracy over extremes in environmental conditions and over time.

The ADE7761 incorporates a fault detection scheme similar to the ADE7751 by continuously monitoring both the phase and neutral currents. A fault is indicated when these currents differ by more than 6.25%.

(continued on Page 3)

15 18

ZERO CROSSING

DETECTION

MISSING NEUTRAL

DETECTION

DIGITAL-TO-FREQUENCY CONVERTER

POWER

SUPPLY MONITOR

ADE7761

SIGNAL PROCESSING

BLOCK

LPF

9 14 17 10 11 12

IN/OUT

16 18 19 20

F1F2CFREVPS0S1SCFDGNDRCLKINREF

04407-0-001

Figure 1.

Rev. A

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

www.analog.com

ADE7761

TABLE OF CONTENTS

General Description......................................................................... 3

Active Power Calculation.......................................................... 15

Specifications..................................................................................... 4

Timing Characteristics..................................................................... 6

Absolute Maximum Ratings............................................................ 7

ESD Caution.................................................................................. 7

Terminology ......................................................................................8

Pin Configuration and Function Descriptions............................. 9

Typical Performance Characteristics ...........................................11

Operation......................................................................................... 13

Power Supply Monitor............................................................... 13

Analog Inputs..............................................................................13

Internal Oscillator ......................................................................14

Analog-to-Digital Conversion.................................................. 14

REVISION HISTORY

2/04—Changed from Rev. 0 to Rev. A.

Digital-to-Frequency Conversion............................................ 18

Transfer Function....................................................................... 18

Fault Detection ...........................................................................19

Missing Neutral Mode ............................................................... 20

Applications..................................................................................... 23

Interfacing to a Microcontroller for Energy Measurement.. 23

Selecting a Frequency for an Energy Meter Application....... 23

Negative Power Information..................................................... 24

Outline Dimensions....................................................................... 25

Ordering Guide .......................................................................... 25

Disclaimer........................................................................................ 26

Changes to Ordering Guide.......................................................... 25

1/04—Revision 0: Initial Version

Rev. A | Page 2 of 28

ADE7761

GENERAL DESCRIPTION

(continued from Page 1)

The ADE7761 incorporates a missing neutral detection scheme by continuously monitoring the input voltage. When a missing neutral condition is detected—no voltage input—the ADE7761 continues billing based on the active current signal (see the Missing Neutral Mode section). The missing neutral condition is indicated when the FAULT pin goes high.

The ADE7761 supplies average active power information on the low frequency outputs F1 and F2. The CF logic output gives instantaneous active power information.

The ADE7761 includes a power supply monitoring circuit on

supply pin. Internal phase matching circuitry ensures

the V

that the voltage and current channels are matched. An internal no-load threshold ensures that the ADE7761 does not exhibit any creep when there is no load.

Rev. A | Page 3 of 28

ADE7761

SPECIFICATIONS

VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, on-chip oscillator, T

Table 1.

Parameter Value Unit Test Conditions/Comments

ACCURACY1

Measurement Error2 0.1 % of reading, typ Over a dynamic range of 500 to 1

Phase Error between Channels

(PF = 0.8 Capacitive) ±0.05 Degrees, max Phase lead 37°

(PF = 0.5 Inductive) ±0.05 Degrees, max Phase lag 60° AC Power Supply Rejection2 Output Frequency Variation 0.01 %, typ V1A = V1B = V2P = ±100 mV rms DC Power Supply Rejection2 Output Frequency Variation 0.01 %, typ V1A = V1B = V2P = ±100 mV rms

FAULT DETECTION

2, 3

See the Fault Detection section

Fault Detection Threshold

Inactive Input <> Active Input 6.25 %, typ (V1A or V1B active) Input Swap Threshold

Inactive Input <> Active Input 6.25 % of larger, typ (V1A or V1B active) Accuracy Fault Mode Operation

V1A Active, V1B = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1

V1B Active, V1A = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1 Fault Detection Delay 3 Seconds, typ Swap Delay 3 Seconds, typ

MISSING NEUTRAL MODE

2, 4

See the Missing Neutral Detection section

Missing Neutral Detection Threshold

V2P − V2N 59.4 mV peak, min Accuracy Missing Neutral Mode

V1A Active, V1B = V2P = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1

V1B Active, V1A = V2P = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1 Missing Neutral Detection Delay 3 Seconds, typ

ANALOG INPUTS V1A − V1N, V1B − V1N, V2P − V2N

Maximum Signal Levels ±660 mV peak, max Differential input 660 mV peak, max Differential input MISCAL − V2N Input Impedance (DC) 400 kΩ, min Bandwidth (−3 dB) 7 kHz, typ ADC Offset Error2 10 mV, max Uncalibrated error, see the Terminology section for details Gain Error ±4 %, typ External 2.5 V reference

REFERENCE INPUT

REF

Input Voltage Range 2.7 V, max 2.5 V + 8%

IN/OUT

2.3 V, min 2.5 V − 8% Input Impedance 4 kΩ, min Input Capacitance 10 pF, max

ON-CHIP REFERENCE

Reference Error ±200 mV, max Temperature Coefficient 30 ppm/°C, typ Current Source 20 µA, min

ON-CHIP OSCILLATOR

Oscillator Frequency 450 kHz Oscillator Frequency Tolerance ±12 % of reading, typ Temperature Coefficient 30 ppm/°C, typ

See footnotes on next page.

MIN

to T

= –40°C to +85°C.

MAX

Rev. A | Page 4 of 28

ADE7761

Parameter Value Unit Test Conditions/Comments

LOGIC INPUTS5

SCF, S1, and S0

Input High Voltage, V Input Low Voltage, V Input Current, IIN ±3 µA, max Typical 10 nA, VIN = 0 V to VDD Input Capacitance, CIN 10 pF, max

LOGIC OUTPUTS5

CF, REVP, and FAULT

Output High Voltage, VOH 4 V, min VDD = 5 V ± 5% Output Low Voltage, VOH 1 V, max VDD = 5 V ± 5%

F1 and F2

Output High Voltage, VOH 4 V, min VDD = 5 V ± 5%, I Output Low Voltage, VOH 1 V, max VDD = 5 V ± 5%, I

POWER SUPPLY For specified performance

VDD 4.75 V, min 5 V − 5%

5.25 V, max 5 V + 5% VDD 4 mA, max

See plots in the Typical Performance Characteristics section.

See the Terminology section for explanation of specifications.

See the Fault Detection section for explanation of fault detection functionality.

See the Missing Neutral Detection section for explanation of missing neutral detection functionality.

Sample tested during initial release and after any redesign or process change that may affect this parameter.

2.4 V, min VDD = 5 V ± 5%

INH

0.8 V, max VDD = 5 V ± 5%

INL

SOURCE

= 10 mA

SINK

= 10 mA

Rev. A | Page 5 of 28

ADE7761

TIMING CHARACTERISTICS

VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, on-chip oscillator, T Sample tested during initial release and after any redesign or process change that may affect this parameter. See Figure 2.

Table 2.

Parameter Value Unit Test Conditions/Comments

120 ms F1 and F2 Pulse Width (Logic High).

t2 See Table 6 s Output Pulse Period. See the Transfer Function section. t3 1/2 t2 s Time between F1 Falling Edge and F2 Falling Edge.

90 ms CF Pulse Width (Logic High).

t5 See Table 7 s CF Pulse Period. See the Transfer Function section. t6 CLKIN/4 s Minimum Time between F1 and F2 Pulse.

The pulse widths of F1, F2, and CF are not fixed for higher output frequencies. See the Transfer Function section.

to T

MIN

Figure 2. Timing Diagram for Frequency Outputs

= –40°C to +85°C.

MAX

04407-0-002

Rev. A | Page 6 of 28

ADE7761

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Table 3.

Parameter Rating

VDD to AGND −0.3 V to +7 V

Analog Input Voltage to AGND

, V

V Reference Input Voltage to AGND −0.3 V to VDD + 0.3 V Digital Input Voltage to DGND −0.3 V to VDD + 0.3 V Digital Output Voltage to DGND −0.3 V to VDD + 0.3 V Operating Temperature Range

Industrial −40°C to +85°C Storage Temperature Range −65°C to +150°C Junction Temperature 150°C 20-Lead SSOP, Power Dissipation 450 mW θJA Thermal Impedance 112°C/W Lead Temperature, Soldering

Vapor Phase (60 s) 215°C

Infrared (15 s) 220°C

, V1N, V2N, V2P, MISCAL

1AP

1BP

−6 V to +6 V

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

Rev. A | Page 7 of 28

ADE7761

TERMINOLOGY

Measurement Error

The error associated with the energy measurement made by the ADE7761 is defined by the following formula:

Erro

Percentag

⎛ ⎜

⎜ ⎝

Phase Error between Channels

The high-pass filter (HPF) in the current channel has a phase lead response. To offset this phase response and equalize the phase response between channels, a phase correction network is also placed in the current channel. The phase correction network ensures a phase match between the current channels and voltage channels to within ±0.1° over a range of 45 Hz to 65 Hz and ±0.2° over a range 40 Hz to 1 kHz.

Power Supply Rejection

This quantifies the ADE7761 measurement error as a percentage of reading when the power supplies are varied. For the ac PSR measurement, a reading at nominal supplies (5 V) is taken. A second reading is obtained with the same input signal levels when an ac (175 mV rms/100 Hz) signal is introduced onto the supplies. Any error introduced by this ac signal is expressed as a percentage of reading (see the Measurement Error definition above).

⎞

7761

EnergyTrue

EnergyTrueADEbyregisteredEnergy

− ×

⎟

%100

⎟ ⎠

For the dc PSR measurement, a reading at nominal supplies (5 V) is taken. A second reading is obtained with the same input signal levels when the power supplies are varied ±5%. Any error introduced is again expressed as a percentage of reading.

ADC Offset Error

This refers to the dc offset associated with the analog inputs to the ADCs. It means that with the analog inputs connected to AGND, the ADCs still see a dc analog input signal. The magnitude of the offset depends on the input range selection (see the Typical Performance Characteristics section). However, when HPFs are switched on, the offset is removed from the current channels and the power calculation is not affected by this offset.

Gain Error

The gain error in the ADE7761 ADCs is defined as the difference between the measured output frequency (minus the offset) and the ideal output frequency. The difference is expressed as a percentage of the ideal frequency, which is obtained from the transfer function (see the Transfer Function section).

Rev. A | Page 8 of 28

ADE7761

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 VDD

Power Supply. This pin provides the supply voltage for the digital circuitry in the ADE7761. The supply voltage should be maintained at 5 V ± 5% for specified operation. This pin should be decoupled with a 10 µF capacitor in parallel with a ceramic 100 nF capacitor.

2, 3 V1A, V1B

Analog Inputs for Channel 1 (Current Channel). These inputs are fully differential voltage inputs with maximum differential input signal levels of ±660 mV with respect to V maximum signal level at these pins is ±1 V with respect to AGND. Both inputs have internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on these inputs without risk of permanent damage.

4 V1N

Negative Input Pin for Differential Voltage Inputs V ±1 V with respect to AGND. The input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on these inputs without risk of permanent damage. The input should be directly connected to the burden resistor and held at a fixed potential,that is, AGND. See the Analog Inputs section.

5 V2N

Negative Input Pin for Differential Voltage Inputs V ±1 V with respect to AGND. The input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on these inputs without risk of permanent damage. The input should be held at a fixed potential, that is, AGND. See the Analog Inputs section.

6 V2P

Analog Inputs for Channel 2 (Voltage Channel). This input is fully differential voltage input with maximum differential input signal levels of ±660 mV with respect to V maximum signal level at these pins is ±1 V with respect to AGND. This input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on these inputs without risk of permanent damage.

7 MISCAL

Analog Input for Missing Neutral Calibration. This pin can be used to calibrate the CF-F1-F2 frequencies in the missing neutral condition. This input is fully differential voltage input with maximum differential input signal levels of +660 mV with respect to V this pin is ±1 V with respect to AGND. This input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on these inputs without risk of permanent damage.

8 AGND

This pin provides the ground reference for the analog circuitry in the ADE7761, that is, ADCs and reference. This pin should be tied to the analog ground plane of the PCB. The analog ground plane is the ground reference for all analog circuitry such as antialiasing filters, and current and voltage transducers. For good noise suppression, the analog ground plane should be connected only to the digital ground plane at the DGND pin.

9 REF

IN/OUT

This pin provides access to the on-chip voltage reference. The on-chip reference has a nominal value of

2.5 V ± 8% and a typical temperature coefficient of 30 ppm/°C. An external reference source can also be connected at this pin. In either case, this pin should be decoupled to AGND with a 1 μF ceramic capacitor and 100 nF ceramic capacitor.

10 SCF

Select Calibration Frequency. This logic input is used to select the frequency on the calibration output CF. Table 6 shows how the calibration frequencies are selected.

11, 12 S1, S0

These logic inputs are used to select one of four possible frequencies for the digital-to-frequency conversion. This offers the designer greater flexibility when designing the energy meter. See the Selecting a Frequency for an Energy Meter Application section.

7 8 9

ADE7761

TOP VIEW

(Not to Scale)

MISCAL

REF

V V

AGND

IN/OUT

SCF

Figure 3. Pin Configuration (SSOP)

20 19 18 17 16 15 14 13 12 11

F1 F2 CF DGND REVP FAULT RCLKIN INT S0 S1

04407-0-003

for specified operation. The

and V1B. The maximum signal level at this pin is

and MISCAL. The maximum signal level at this pin is

for specified operation. The

for specified operation. The maximum signal level at

Rev. A | Page 9 of 28

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