ADE7760 Ver la hoja de datos (PDF) - Analog Devices
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ADE7760 Datasheet PDF : 24 Pages
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ADE7760
Note that if the on-chip reference is used, actual output
frequencies may vary from device to device due to reference
tolerance of ±8%.
5.70× 0.66 × 0.66 × 1.72 Hz
F1 − F2 Frequency =
2 × 2 ×2.52
= 0.34 Hz
CF Frequency = F1 − F2 × 64 = 22.0 Hz
As can be seen from these two example calculations, the
maximum output frequency for ac inputs is always half of that
for dc input signals. Table 7 shows a complete listing of all
maximum output frequencies for ac signals.
Table 7. Maximum Output Frequency on CF, F1, and F2 for
AC Inputs
F1, F2 Maximum CF Maximum
Frequency
Frequency
SCF S1 S0 (Hz)
(Hz)
CF to
F1
Ratio
1 0 0 0.34
43.52
128
0 0 0 0.34
21.76
64
1 0 1 0.68
43.52
64
0 0 1 0.68
21.76
32
1 1 0 1.36
43.52
32
0 1 0 1.36
21.76
16
1 1 1 2.72
43.52
16
0 1 1 2.72
5570
2048
FAULT DETECTION
The ADE7760 incorporates a novel fault detection scheme that
warns of fault conditions and allows the ADE7760 to continue
accurate billing during a fault event. The ADE7760 does this by
continuously monitoring both the phase and neutral (return)
currents. A fault is indicated when these currents differ by more
than 6.25%. However, even during a fault, the output pulse rate
on F1 and F2 is generated using the larger of the two currents.
Because the ADE7760 looks for a difference between the voltage
signals on V1A and V1B, it is important that both current
transducers be closely matched.
On power-up, the output pulse rate of the ADE7760 is pro-
portional to the product of the voltage signals on V1A and
Channel 2. If there is a difference of greater than 6.25% between
V1A and V1B on power-up, the fault indicator (FAULT) becomes
active after about 1 s. In addition, if V1B is greater than V1A, the
ADE7760 selects V1B as the input. The fault detection is
automatically disabled when the voltage signal on Channel 1 is
less than 0.3% of the full-scale input range. This eliminates false
detection of a fault due to noise at light loads.
Fault with Active Input Greater than Inactive Input
If V1A is the active current input (that is, is being used for
billing), and the voltage signal on V1B (inactive input) falls below
93.75% of V1A, the fault indicator becomes active. Both analog
inputs are 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 23 shows one condition under which
FAULT becomes active. Because V1A is the active input and it is
still greater than V1B, billing is maintained on V1A, that is, no
swap to the V1B input occurs. V1A remains the active input.
V1A
V1B
V1A
V1A
0V
V1N
AGND
V1B
FILTER FAULT
AND
A COMPARE
TO
MULTIPLIER
B
V1B < 93.75% OF V1A
V1B
FAULT
<0
>0
6.25% OF ACTIVE INPUT
ACTIVE POINT – INACTIVE INPUT
Figure 23. Fault Conditions for Active Input Greater than Inactive Input
Fault with Inactive Input Greater than Active Input
Figure 24 illustrates another fault condition. If the difference
between V1B, the inactive input, and V1A, the active input (used
for billing), becomes greater than 6.25% of V1B, the FAULT
indicator goes active, and there is also a swap over to the V1B
input. The analog input V1B becomes the active input. Again,
there is a time constant of about 3 s associated with this swap.
V1A does not swap back to being the active channel until V1A is
greater than V1B and the difference between V1A and V1B—in this
order—becomes greater than 6.25% of V1A. The FAULT
indicator, however, becomes inactive as soon as V1A is within
6.25% of V1B. This threshold eliminates potential chatter
between V1A and V1B.
V1A
V1B
V1A
V1A
0V
V1N
AGND
V1B
FILTER FAULT
AND
A COMPARE
TO
MULTIPLIER
B
V1A < 93.75% OF V1B
V1B
FAULT + SWAP
<0
>0
6.25% OF INACTIVE INPUT
ACTIVE POINT – INACTIVE INPUT
Figure 24. Fault Conditions for Inactive Input Greater than Active Input
Rev. 0 | Page 17 of 24
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