Energy Metering IC with On-Chip

Fault and Missing Neutral Detection

ADE7761

Rev. A

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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

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 require-

ments 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 multi-

plication 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%.

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FUNCTIONAL BLOCK DIAGRAM

MISCAL

ADC

6

5

ADC

ADC

4

3

7

ADC

2

AGND

FAULT

2.5V

REFERENCE

INTERNAL

OSCILLATOR

MISSING NEUTRAL

GAIN ADJUST

MISSING NEUTRAL

DETECTION

9

14

17

10

11

12

B>A

A<>B

A>B

ZERO CROSSING

DETECTION

ADE7761

SIGNAL PROCESSING

BLOCK

15

1

8

POWER

SUPPLY MONITOR

DIGITAL-TO-FREQUENCY CONVERTER

16

18

19

20

F1

F2

CF

REVP

S0

S1

SCF

DGND

RCLKIN

HPF

LPF

4k

Ω

Figure 1.