ADE7761ARSRL datasheet(13/28 Pages) AD

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ADE7761

Rev. A | Page 13 of 28

OPERATION

POWER SUPPLY MONITOR

The ADE7761 contains an on-chip power supply monitor. The

power supply (VDD) is continuously monitored by the ADE7761.

If the supply is less than 4 V ± 5%, the ADE7761 goes into an

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

and F2 outputs are 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.

ADE7761

REVP - FAULT - CF -

F1 - F2 OUTPUTS

INACTIVE

ACTIVE

TIME

INACTIVE

VDD

Figure 9. On-Chip Power Supply Monitoring

ANALOG INPUTS

Channel V1 (Current Channel)

The voltage outputs from the current transducers are connected

to the ADE7761 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 10 shows the maximum signal levels on V1A, V1B, and V1N.

The differential voltage signal on the inputs must be referenced

to a common mode (usually AGND).

VCM

+660mV + VCM

–660mV + VCM

DIFFERENTIAL INPUT B

±660mV MAX PEAK

V1B

V1N

V1A

VCM

COMMON MODE

±100mV MAX

DIFFERENTIAL INPUT A

±660mV MAX PEAK

AGND

V1A, V1B

Figure 10. Maximum Signal Levels, Channel 1

Channel V2 (Voltage Channel)

The output of the line voltage transducer is connected to the

ADE7761 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 11 shows the

maximum signal levels that can be connected to Channel 2.

VCM

+660mV + VCM

–660mV + VCM

COMMON MODE

±100mV MAX

V2N

V2P

VCM

DIFFERENTIAL INPUT

±660mV MAX PEAK

Figure 11. Maximum Signal Levels, Channel 2

The differential voltage V2P–V2N must be referenced to a

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

ADE7761 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.

MISCAL Input

The input for the power calibration in missing neutral mode is

connected to the ADE7761 at this analog input. MISCAL is a

single-ended voltage input. It is recommended to use a dc signal

derived from the voltage reference to drive this pin. The maxi-

mum peak differential signal on MISCAL is +660 mV with

respect to V2N. Figure 12 shows the maximum signal levels that

can be connected to the MISCAL pin.

VCM

+660mV + VCM

COMMON MODE

±100mV MAX

V2N

MISCAL

VCM

MISCAL

DIFFERENTIAL INPUT

±660mV MAX PEAK

MISCAL

AGND

Figure 12. Maximum Signal Levels, MISCAL

The differential voltage MISCAL–V2N must be referenced to a

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

ADE7761 can be driven with common-mode voltages of up to

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

achieved using a common mode equal to AGND.

Typical Connection Diagrams

Figure 13 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 analog ground (AGND); the common-mode

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