ADE7761BARS-REF AD [Analog Devices], ADE7761BARS-REF Datasheet - Page 19

• Manufacturer Part Number: ADE7761BARS-REF
• Description: Energy Metering IC with On-Chip Fault and Missing Neutral Detection
• Manufacturer: AD [Analog Devices]

The ADE7761B detects a missing neutral condition by continu-
ously monitoring the voltage channel input (V
FAULT pin is held high when a missing neutral condition is
detected. In this mode, the ADE7761B continues to bill the energy
based on the signal level on the current channel (see Figure 32).
The billing rate or frequency outputs can be adjusted by changing
the dc level on the MISCAL pin.
Important Note for Billing of Active Energy
The ADE7761B provides pulse outputs, CF, F1, and F2, that are
intended to be used for the billing of active energy. Pulses are
generated at these outputs in two different situations.
Case 1
When the analog input V
described in Figure 34, the CF, F
tional to active power and can be used to bill active energy.
Case 2
When the analog input V
conditions described in Figure 34, the ADE7761B does not
measure active energy but a quantity proportional to kAh. This
quantity is used to generate pulses on the same CF, F1, and F2.
This situation is indicated when the FAULT pin is high.
GENERATOR
1
V
V
V
MISCAL
RB + VR = RF.
1A
1N
1B
244V rms
POWER
LOAD
Figure 32. Energy Calculation in Missing Neutral Mode
Figure 31. Missing Neutral System Diagram
ADC
ADC
ADC
IB
A > B
B > A
A ≠ B
GAIN ADJUSMTENT
MISSING NEUTRAL
2P
2P
− V
HPF
− V
2N
1
2N
RA
, and F
RB
complies with the conditions
VR
CT
CT
does not comply with the
1
DETECTION
1
1
CROSSING
ZERO
RB
RB
2
R
frequencies are propor-
C
F
C
F
F
0V
V
R
R
1A
F
F
V
V
2P
2P
2N
C
C
− V
V
V
V
F
F
1A
1N
1B
CONVERTERS
CF F1 F2
FREQUENCY
DIGITAL-TO-
2N
). The
LPF
Rev. 0 | Page 19 of 24
Analog Devices cautions users of the ADE7761B about the
following:
• Billing active energy in Case 1 is consistent with the under-
• Billing active energy while the ADE7761B is in Case 2 must
Missing Neutral Detection
The ADE7761B continuously monitors the voltage input and
detects a missing neutral condition when the voltage input peak
value is smaller than 9% of the analog full scale or when no zero
crossings are detected on this input (see Figure 33).
The ADE7761B leaves the missing neutral mode for normal
operation when both conditions are no longer valid; that is,
a voltage peak value of greater than 9% of full scale and zero
crossing on the voltage channel is detected (see Figure 34).
AGND
|V2|
AGND
9% OF FS
standing of the quantity represented by pulses on the CF, F1,
and F2 outputs (watthour).
be decided knowing that the entity measured by the ADE7761B
in this case is ampere-hour and not watthour. Users should
be aware of this limitation and decide if the ADE7761B is
appropriate for their application.
PEAK
Figure 34. Return to Normal Mode After Missing Neutral Detection
V2
V2
V
0V
FS
2P
< 9% OF FULL SCALE
– V
V
V
V
V
2P
2P
2N
2N
2N
Figure 33. Missing Neutral Detection
|V2|
+9% OF FS
–9% OF FS
ZERO CROSSING ON V2
PEAK
> 9% OF FULL SCALE
V
V
0V
FS
FS
2P
2P
OR
AND
– V
– V
ADC
ADC
2N
2N
NO ZERO CROSSING ON V2
THRESHOLD
THRESHOLD
FILTER AND
FILTER AND
V
0V
FS
2P
– V
ADE7761B
2N
MISSING
NEUTRAL
MISSING
NEUTRAL