ADE7761B

Rev. 0 | Page 17 of 24

S1

S0

0

0

1.72

0

1

3.44

1

0

6.86

1

1

13.7

internal oscillator frequency (OSC).

Frequency Output CF

The pulse output calibration frequency (CF) is intended for use

during calibration. The output pulse rate on CF can be up to

frequency selected, the higher the CF scaling. Table 7 shows

how the two frequencies are related, depending on the states of

Logic Input S0, Logic Input S1, and Logic Input SCF. Because of

its relatively high pulse rate, the frequency at this logic output is

after multiplication. However, because the output frequency is high,

this active power information is accumulated over a much shorter

time. Therefore, less averaging is carried out in the digital-to-

frequency conversion. With much less averaging of the active

power signal, the CF output is much more responsive to power

fluctuations (see Figure 22).

Table 7. Relationship Between CF and F1, F2 Frequency

Outputs

SCF

S1

S0

CF Frequency Output

1

0

0

1.72

0

0

0

1.72

1

0

1

3.44

0

0

1

3.44

1

1

0

6.86

0

1

0

6.86

1

1

1

13.7

0

1

1

13.7

Example

In this example, if ac voltages of ±660 mV peak are applied to

Channel V1 and Channel V2, the expected output frequency on

CF, F1, and F2 is calculated as

Gain

= 1, PGA = 0

= 1.7 Hz, SCF = S1 = S0 = 0

= rms of 660 mV peak ac = 0.66/√2 V

= rms of 660 mV peak ac = 0.66/√2 V

= 2.5 V (nominal reference value)

Note that if the on-chip reference is used, actual output

frequencies may vary from device to device due to a reference

tolerance of ±8%.

Hz

367

.

0

5

.

2

2

2

Hz

72

.

1

66

.

0

66

.

0

13

.

6

,

2

2

1

=

×

×

×

×

×

=

Frequency

F

F

CF Frequency

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 8 shows a complete listing of all maximum output

frequencies for ac signals.

Table 8. Maximum Output Frequencies on CF, F1, and F2 for

AC Inputs

SCF

S1

S0

Frequency (Hz),

CF Maximum

Frequency (Hz),

Ratio

1

0

0

0.37

46.98

128

0

0

0

0.37

23.49

64

1

0

1

0.73

46.98

64

0

0

1

0.73

23.49

32

1

1

0

1.47

46.98

32

0

1

0

1.47

23.49

16

1

1

1

2.94

46.98

16

0

1

1

2.94

6013

2048

FAULT DETECTION

The ADE7761B incorporates a novel fault detection scheme

that warns of fault conditions and allows the ADE7761B to

continue accurate billing during a fault event. The ADE7761B

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 ADE7761B looks for a difference between

current transducers be closely matched.

On power-up, the output pulse rate of the ADE7761B is propor-

6.25%, the fault indicator (FAULT) becomes active after about

when the voltage signal on Channel V1 is less than 0.3% of the

full-scale input range. This eliminates false detection of a fault

due to noise at light loads.