ADE7760

Rev. 0 | Page 19 of 24

APPLICATIONS

INTERFACING TO A MICROCONTROLLER FOR

ENERGY MEASUREMENT

The easiest way to interface the ADE7760 to a microcontroller

is to use the CF high frequency output with the output fre-

quency scaling set to 2048 × F1, F2. This is done by setting

SCF = 0 and S0 = S1 = 1 (see Table 7). With full-scale ac signals

on the analog inputs, the output frequency on CF is approxi-

mately 5.5 kHz. Figure 26 illustrates one scheme that could be

used to digitize the output frequency and carry out the

necessary averaging mentioned in the previous section.

TIME

±10%

AVERAGE

FREQUENCY

CF

FREQUENCY

RIPPLE

MCU

UP/DOWN

COUNTER

LOGIC

CF

REVP*

ADE7760

FAULT**

*REVP MUST BE USED IF THE METER IS BIDIRECTIONAL OR

DIRECTION OF ENERGY FLOW IS NEEDED.

**FAULT MUST BE USED TO RECORD ENERGY IN FAULT CONDITION.

Figure 26. Interfacing the ADE7760 to an MCU

As shown, the frequency output CF is connected to an MCU

counter or port, which counts the number of pulses in a given

integration time, determined by an MCU internal timer. The

average power, proportional to the average frequency, is given

by

Timer

Counter

Power

Active

Average

Frequency

Average

=

=

The energy consumed during an integration period is given by

Counter

Time

Time

Counter

Time

Power

Average

Energy

=

×

=

×

=

For the purpose of calibration, this integration time could be

10 s to 20 s in order to accumulate enough pulses to ensure

correct averaging of the frequency. In normal operation, the

integration time could be reduced to 1 s or 2 s depending, for

example, on the required update rate of a display. With shorter

integration times on the MCU, the amount of energy in each

update might still have a small amount of ripple, even under

steady load conditions. However, over a minute or more, the

measured energy has no ripple.

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 to be used to drive the

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 impulses/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 impulses/kWh.

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

F1 and F2 (Hz)

12.5 A

0.083

25 A

0.166

40 A

0.266

60 A

0.4

80 A

0.533

120 A

0.8

output frequencies on F1 and F2. When designing an energy

meter the nominal design voltage on Channel 2 (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 accommodates

overcurrent signals and signals with high crest factors. Table 9

shows the output frequency on F1 and F2 when both analog

inputs are half-scale. The frequencies listed in Table 9 align well

with those listed in Table 8 for maximum load.