ADE7761B
Rev. 0 | Page 11 of 24
THEORY OF OPERATION
POWER SUPPLY MONITOR
The ADE7761B continuously monitors the power supply (V
DD
)
with its on-chip power supply monitor. If the supply is less than
4 V ± 5%, the ADE7761B 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 that provide 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 V
DD
does not exceed 5 V ± 5%, as specified for
normal operation.
ADE7761B
REVP - FAULT - CF -
F1 - F2 OUTPUTS
INACTIVE ACTIVE
TIME
INACTIVE
DD
5V
4V
0V
06797-009
Figure 11. On-Chip, Power Supply Monitoring
ANALOG INPUTS
Channel V1 (Current Channel)
The voltage outputs from the current transducers are connected
to the ADE7761B at Channel V1. It has two voltage inputs, V
1A
and V
1B
. These inputs are fully differential with respect to V
1N
.
However, at any one time, only one input is selected to perform
the power calculation (see the
Fault Detection section).
The maximum peak differential signal on V
1A
− V
1N
and V
1B
− V
1N
is ±660 mV. However, Channel V1 has a programmable gain
amplifier (PGA) with user-selectable gains of 1 and 16 (see
Table 5). This gain facilitates easy transducer interfacing.
Table 5. Channel V1 Dynamic Range
PGA Gain Maximum Differential Signal (mV)
0 1 660
1 16 41
Figure 12 shows the maximum signal levels on V
1A
, V
1B
, and
V
1N
. The maximum differential voltage is ±660 mV divided by
the gain selection. The differential voltage signal on the inputs
must be referenced to a common mode (usually AGND).
V
CM
DIFFERENTIAL INPUT B
±660mV MAX PEAK V
1B
V
1N
1A
V1
V1
V
CM
COMMON MODE
±100mV MAX
DIFFERENTIAL INPUT A
±660mV MAX PEAK
AGND
V
1A
, V
1B
+660mV
GAIN
–660mV
GAIN
+ V
CM
+ V
CM
06797-010
Figure 12. Maximum Signal Levels, Channel V1
Channel V2 (Voltage Channel)
The output of the line voltage transducer is connected to the
ADE7761B at this analog input. Channel V2 is a single-ended
voltage input. The maximum peak differential signal on
Channel V2 is ±660 mV with respect to V
2N
. Figure 13 shows the
maximum signal levels that can be connected to Channel V2.
V
CM
+660mV + V
CM
–660mV + V
CM
COMMON MODE
±100mV MAX
V
2N
V
2P
V
CM
V2
DIFFERENTIAL INPUT
±660mV MAX PEAK
2
06797-011
Figure 13. Maximum Signal Levels, Channel V2
The differential voltage V
2P
− V
2N
must be referenced to a
common mode (usually AGND). The analog inputs of the
ADE7761B 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 ADE7761B 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
maximum peak differential signal on MISCAL is 660 mV with
respect to V
2N
. Figure 14 shows the maximum signal levels that
can be connected to the MISCAL pin.
V
CM
+660mV + V
CM
COMMON MODE
±100mV MAX
V
2N
MISCAL
V
CM
MISCAL
DIFFERENTIAL INPUT
±660mV MAX PEAK
MISCAL
AGND
06797-012
Figure 14. Maximum Signal Levels, MISCAL
The differential voltage, MISCAL − V
2N
, must be referenced
to a common mode (usually AGND). The analog inputs of the
ADE7761B 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.
