ADE7769

Rev. A | Page 15 of 20

S1

S0

0

0

0.86

0

1

1.72

1

0

3.43

1

1

6.86

Example

In this example, with ac voltages of ±30 mV peak applied to

V1 and ±165 mV peak applied to V2, the expected output

frequency is calculated as

If the on-chip reference is used, actual output frequencies

may vary from device to device due to the reference tolerance

of ±200 mV.

175

.

0

204

.

0

45

.

2

2

2

165

.

0

03

.

0

75

.

494

2

=

×

=

×

×

×

×

×

=

1

1

F

F

Freq

(11)

Table 6. Maximum Output Frequency on F1 and F2

S1

S0

OSC Relation

0

0

0.175

0

1

0.35

1

0

0.70

1

1

1.40

Frequency Output CF

The pulse output CF (calibration frequency) is intended for

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

frequency selected, the higher the CF scaling (except for the

high frequency mode SCF = 0, S1 = S0 = 1). Table 7 shows how

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

logic inputs S0, S1, and SCF. Due to its relatively high pulse

rate, the frequency at the CF logic output is proportional to the

instantaneous real power. As with F1 and F2, CF is derived

from the output of the low-pass filter after multiplication.

However, because the output frequency is high, this real

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 real

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

fluctuations (see the signal processing block diagram shown in

Figure 15).

Table 7. Maximum Output Frequency on CF

SCF

S1

S0

1

0

0

128 × F1, F2 = 22.4

0

0

0

64 × F1, F2 = 11.2

1

0

1

64 × F1, F2 = 22.4

0

0

1

32 × F1, F2 = 11.2

1

1

0

32 × F1, F2 = 22.4

0

1

0

16 × F1, F2 = 11.2

1

1

1

16 × F1, F2 = 22.4

0

1

1

2048 × F1, F2 = 2.867 kHz

SELECTING A FREQUENCY FOR AN ENERGY

METER APPLICATION

As shown in Table 5, the user can select one of four frequencies.

This frequency selection determines the maximum frequency

on F1 and F2. These outputs are intended for driving an energy

register (electromechanical or other). Because only four

different output frequencies can be selected, the available

frequency selection has been optimized for a meter constant

of 100 imp/kWh with a maximum current of between 10 A

and 120 A. Table 8 shows the output frequency for several

cases, the meter constant is 100 imp/kWh.

Table 8. F1 and F2 Frequency at 100 imp/kWh

F1 and F2 (Hz)

12.5

0.076

25.0

0.153

40.0

0.244

60.0

0.367

80.0

0.489

120.0

0.733

output frequencies (F1, F2). When designing an energy meter,

the nominal design voltage on Channel V2 (voltage) should be

set to half-scale to allow for calibration of the meter constant.

The current channel should also be no more than half scale

when the meter sees maximum load. This allows overcurrent

signals and signals with high crest factors to be accommodated.

Table 9 shows the output frequency on F1 and F2 when both

analog inputs are half scale. The frequencies in Table 9 align

very well with those in Table 8 for maximum load.

Table 9. F1 and F2 Frequency with Half-Scale AC Inputs

S1

S0

Frequency on F1 and F2—

0

0

0.86

0.044 Hz

0

1

1.72

0.088 Hz

1

0

3.43

0.176 Hz

1

1

6.86

0.352 Hz