ADE7761 datasheet(22/28 Pages) AD

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ADE7761

Rev. A | Page 22 of 28

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operation when both conditions are no longer valid—voltage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).

FILTER AND

THRESHOLD

V2P

V2N

AGND

ADC

MISSING

NEUTRAL

|V2|PEAK > 9% OF FULL SCALE

AND

ZERO-CROSSING ON V2

+9% OF FS

–9% OF FS

V2P–V2N

Figure 32. Return to Normal Mode after Missing Neutral Detection

Missing Neutral Gain Calibration

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

mode by replacing V2rms by MISCALrms √2:

REF

rms

MISCAL

Frequency

−

(8)

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).

VREF is the reference voltage (2.5 V ± 8%) (V).

F1-4 is one of four possible frequencies selected by using the

logic inputs S0 and S1 (see Table 5).

Example

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:

F1–4 = 1.7 Hz, SCF = S1 = S0 = 0

V1 = rms of 330 mV peak ac = 0.33/√2 V

V2 = rms of 330 mV peak ac = 0.33/√2 V

VREF = 2.5 V (nominal reference value)

084

−

frequency

Frequency

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

084

frequency

Frequency

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