ADE7761
The ADE7761 leaves the missing neutral mode for normal
operation when both conditions are no longer valid—voltage
peak value greater than 9% of full scale and zero crossing on the
voltage channel detected (see Figure 32).
where:
F1, F2 Frequency is the output frequency on F1 and F2 (Hz).
V1rms is the differential rms voltage signal on Channel 1 (V).
MISCALrms is the differential rms voltage signal on the MISCAL
pin (V).
V
MISSING
2P
NEUTRAL
FILTER AND
THRESHOLD
V
REF is the reference voltage (2.5 V 8%) (V).
V2
ADC
F
1-4 is one of four possible frequencies selected by using the
V
2N
AGND
logic inputs S0 and S1 (see Table 5).
Example
|V2|
PEAK
> 9% OF FULL SCALE
AND
ZERO-CROSSING ON V2
In normal mode, ac voltages of 330 mV peak are applied to V1
and V2, and then the expected output frequency on F1 and F2 is
calculated as follows:
V
–V
2P 2N
FS
F
1–4 = 1.7 Hz, SCF = S1 = S0 = 0
+9% OF FS
–9% OF FS
V1 = rms of 330 mV peak ac = 0.33/√ V
2
V2 = rms of 330 mV peak ac = 0.33/√ V
2
Figure 32. Return to Normal Mode after Missing Neutral Detection
V
REF = 2.5 V (nominal reference value)
Missing Neutral Gain Calibration
5.70×0.33×0.33×1.7 Hz
When the ADE7761 is in missing neutral mode, the energy is
billed based on the active current input signal level. The
calibration of the frequency outputs in this mode can be done
with the MISCAL analog input pin. In this mode, applying a dc
voltage of 330 mV on MISCAL is equivalent to applying, in
normal mode, a pure sine wave on the voltage input with a peak
value of 330 mV. The MISCAL input can vary from 0 V to
660 mV (see the Analog Inputs section). When set to 0 V, the
frequency outputs are close to zero. When set to 660 mV dc, the
frequency outputs are twice that when MISCAL is at 330 mV
dc. In other words, Equation 7 can be used in missing neutral
F1 , F2 Frequency =
= 0.084 Hz
2 × 2 ×2.52
CF Frequency = F1 − F2 frequency × 64 = 5.4 Hz
In missing neutral mode, ac voltage of 330 mV peak is applied
to V1, no signal is connected on V2, and 330 mV dc input is
applied to MISCAL. With the ADE7761 in the same configura-
tion as the previous example, the expected output frequencies
on CF, F1, and F2 are
5.70×0.33×0.33/ 2 ×1.7 Hz
F1 , F2 Frequency =
= 0.084 Hz
mode by replacing V2rms by MISCALrms √ :
2 × 2.52
2
CF Frequency = F1 , F2 frequency × 64 = 5.4 Hz
5.70 × MISCALrms / 2 × F1−4
F1 , F2 Frequency =
(8)
2
VREF
Rev. A | Page 22 of 28
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