Energy Metering IC with On-Chip Fault and

Missing Neutral Detection

ADE7761A

Rev. 0

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FEATURES

High accuracy, active energy measurement IC supports

IEC 62053-21

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 shunt and

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 ADE7761A 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 IEC 62053-21 standard. The only analog circuitry

used on the ADE7761A 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 ADE7761A incorporates a fault

detection scheme similar to the ADE7751 by continuously

monitoring both phase and neutral currents. A fault is indicated

when the currents differ by more than 6.25%.

The ADE7761A incorporates a missing neutral detection

scheme by continuously monitoring the input voltage. When a

missing neutral condition is detected—no voltage input—the

ADE7761A 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

ADE7761A supplies average active power information on the

low frequency outputs, F1 and F2. The CF logic output gives

instantaneous active power information.

The ADE7761A includes a power-supply monitoring circuit on

that the voltage and current channels are matched. An internal

no-load threshold ensures that the ADE7761A does not exhibit

any creep when there is no load.

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

ADE7761A

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

3k

Ω

PGA

13

Figure 1.