ADE7761ARS-REF Analog Devices Inc, ADE7761ARS-REF Datasheet - Page 20

• Manufacturer Part Number: ADE7761ARS-REF
• Description: IC ENERGY METERING 20-SSOP
• Manufacturer: Analog Devices Inc

Specifications of ADE7761ARS-REF

• Rohs Status: RoHS non-compliant

ADE7761
Fault with Active Input Greater than Inactive Input
If V
and the voltage signal on V
of V
filtered and averaged to prevent false triggering of this logic
output. As a consequence of the filtering, there is a time delay of
approximately 3 s on the logic output FAULT after the fault
event. The FAULT logic output is independent of any activity on
outputs F1 or F2. Figure 26 shows one condition under which
FAULT becomes active. Because V
still greater than V
swap to the V
Fault with Inactive Input Greater than Active Input
Figure 27 illustrates another fault condition. If the difference
between V
being used for billing), becomes greater than 6.25% of V
FAULT indicator goes active, and there is also a swap over to the
V
there is a time constant of about 3 s associated with this swap.
V
greater than V
order—becomes greater than 6.25% of V
FAULT indicator becomes inactive as soon as V
6.25% of V
between V
0V
0V
1B
1A
Figure 26. Fault Conditions for Active Input Greater than Inactive Input
Figure 27. Fault Conditions for Inactive Input Greater than Active Input
1A
input. The analog input V
does not swap back to being the active channel until V
1A
V
V
<0
FAULT
is the active current input (that is, being used for billing),
, the fault indicator becomes active. Both analog inputs are
1B
1A
FAULT + SWAP
<0
6.25% OF ACTIVE INPUT
6.25% OF INACTIVE INPUT
< 93.75% OF V
< 93.75% OF V
V
V
V
V
1A
1A
1B
1B
1B
1A
1B
, the inactive input, and V
. This threshold eliminates potential chatter
and V
1B
AGND
1B
AGND
input occurs. V
and the difference between V
1B
1B
1A
1B
, billing is maintained on V
.
>0
V
V
V
V
1A
1B
1A
1B
>0
1B
V
V
V
V
V
V
1A
1N
1B
1A
1N
1B
(inactive input) falls below 93.75%
1B
ACTIVE POINT – INACTIVE INPUT
1A
ACTIVE POINT – INACTIVE INPUT
becomes the active input. Again,
remains the active input.
1A
is the active input and it is
1A
, the active input (that is,
A
B
A
B
1A
. However, the
COMPARE
COMPARE
FILTER
FILTER
AND
AND
1A
1A
1A
and V
, that is, no
is within
FAULT
TO
MULTIPLIER
FAULT
TO
MULTIPLIER
1B
—in this
1B
, the
1A
Rev. A | Page 20 of 28
is
Calibration Concerns
Typically, when a meter is being calibrated, the voltage and
current circuits are separated as shown in Figure 28. This means
that current passes through only the phase or neutral circuit.
Figure 28 shows current being passed through the phase circuit.
This is the preferred option, because the ADE7761 starts billing
on the input V
nected to V
neutral circuit, the FAULT indicator comes on under these
conditions. However, this does not affect the accuracy of the
calibration and can be used as a means to test the functionality
of the fault detection.
If the neutral circuit is chosen for the current circuit in the
arrangement shown in Figure 28, this may have implications for
the calibration accuracy. The ADE7761 powers up with the V
input active as normal. However, because there is no current in
the phase circuit, the signal on V
be flagged and the active input to be swapped to V
The meter can be calibrated in this mode, but the phase and
neutral CTs might differ slightly. Because under no-fault condi-
tions all billing is carried out using the phase CT, the meter
should be calibrated using the phase circuit. Of course, both
phase and neutral circuits can be calibrated.
MISSING NEUTRAL MODE
The ADE7761 integrates a novel fault detection that warns and
allows the ADE7761 to continue to bill in case a meter is
connected to only one wire (see Figure 29). For correct
operation of the ADE7761 in this mode, the V
ADE7761 must be maintained within the specified range (5 V ±
5%). The missing neutral detection algorithm is designed to
work over a line frequency of 45 Hz to 55 Hz.
CURRENT
TEST
Figure 28. Fault Conditions for Inactive Input Greater than Active Input
IB
IB
1A
240V RMS
in the diagram. Since there is no current in the
1A
V
on power-up. The phase circuit CT is con-
AGND
RA*
RB*
VR*
*RB + VR = RF
CT
CT
RB
RB
C
F
1A
is zero. This causes a fault to
R
0V
V
F
1A
C
R
R
T
F
F
V
V
2P
2N
C
C
DD
F
F
V
V
V
1A
1N
1B
pin of the
1B
(neutral).
1A