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ADE7760

Energy Metering IC with On-Chip Fault Detection

Analog Devices 

OPERATION

POWER SUPPLY MONITOR

The ADE7760 contains an on-chip power supply monitor. The

power supply (VDD) is continuously monitored by the ADE7760.

If the supply is less than 4 V ± 5%, the ADE7760 goes into an

inactive state, that is, no energy is accumulated and the CF, F1,

and F2 outputs is disabled. This is useful to ensure correct

device operation at power-up and during power-down. The

power supply monitor has built-in hysteresis and filtering. This

gives a high degree of immunity to false triggering due to noisy

supplies.

The power supply and decoupling for the part should be such

that the ripple at VDD does not exceed 5 V ± 5% as specified for

normal operation.

VDD

5V

4V

0V

ADE7760

REVP - FAULT - CF - INACTIVE

F1 - F2 OUTPUTS

TIME

ACTIVE

INACTIVE

Figure 8. On-Chip Power Supply Monitoring

ANALOG INPUTS

Channel V1 (Current Channel)

The voltage outputs from the current transducers are connected

to the ADE7760 here. Channel V1 has two voltage inputs, V1A

and V1B. These inputs are fully differential with respect to V1N.

However, at any one time, only one is selected to perform the

power calculation (see the Fault Detection section).

The maximum peak differential signal on V1A–V1N and V1B–V1N

is ±660 mV. Figure 9 shows the maximum signal levels on V1A,

V1B, and V1N. The differential voltage signal on the inputs must

be referenced to a common mode such as AGND.

V1A, V1B

+660mV + VCM

VCM

–660mV + VCM

DIFFERENTIAL INPUT A

±660mV MAX PEAK

COMMON MODE

±100mV MAX

VCM

AGND

DIFFERENTIAL INPUT B

±660mV MAX PEAK

V1A

V1

V1N

V1

V1B

Figure 9. Maximum Signal Levels, Channel 1

ADE7760

Channel V2 (Voltage Channel)

The output of the line voltage transducer is connected to the

ADE7760 at this analog input. Channel V2 is a single-ended

voltage input. The maximum peak differential signal on

Channel 2 is ±660 mV with respect to V2N. Figure 10 shows the

maximum signal levels that can be connected to Channel 2.

V2

+660mV + VCM

VCM

–660mV + VCM

DIFFERENTIAL INPUT

±660mV MAX PEAK

COMMON MODE

±100mV MAX

V2P

V2

V2N

VCM

Figure 10. Maximum Signal Levels, Channel 2

The differential voltage V2P–V2N must be referenced to a

common mode (usually AGND). The analog inputs of the

ADE7760 can be driven with common-mode voltages of up to

100 mV with respect to AGND. However, the best results are

achieved using a common mode equal to AGND.

Typical Connection Diagrams

Figure 11 shows a typical connection diagram for Channel V1.

The analog inputs are being used to monitor both the phase and

neutral currents. Because of the large potential difference

between the phase and neutral, two current transformers (CTs)

must be used to provide the isolation. Note that both CTs are

referenced to AGND (analog ground); the common-mode

voltage is, therefore, 0 V. The CT turns ratio and burden resistor

(RB) are selected to give a peak differential voltage of ±660 mV.

RF

V1A

CT

RB

IP IN AGND

RB

CF

V1N

CF

CT

RF

V1B

Figure 11. Typical Connection for Channel 1

Figure 12 shows two typical connections for Channel V2. The

first option uses a potential transformer (PT) to provide

complete isolation from the main voltage. In the second option,

the ADE7760 is biased around the neutral wire, and a resistor

divider is used to provide a voltage signal that is proportional to

the line voltage. Adjusting the ratio of RA and RB + VR is a

convenient way of carrying out a gain calibration on the meter.

Rev. 0 | Page 11 of 24

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