ADE7953 datasheet(33/68 Pages) AD

33 / 68 page

Data Sheet

ADE7953

Rev. A | Page 33 of 68

ENERGY-TO-FREQUENCY CONVERSION

The ADE7953 provides two energy-to-frequency conversions for

calibration purposes. After initial calibration at manufacturing,

the manufacturer or end customer is often required to verify the

meter accuracy. One convenient way to do this is to provide an

output frequency that is proportional to the active, reactive, or

apparent power, or to the current rms under steady load condi-

tions. This output frequency provides a simple single-wire

interface that can be optically isolated to interface to external

calibration equipment. The ADE7953 includes two fully

programmable calibration frequency output pins: CF1 (Pin 23)

and CF2 (Pin 24). The energy-to-frequency conversion is

illustrated in Figure 57.

DFC

CFxDEN

CFx PULSE

OUTPUT

CFxSEL BITS

IN CFMODE REGISTER

IRMS

VAR

WATT

IRMSA + IRMSB

AWATT + BWATT

Figure 57. Energy-to-Frequency Conversion

Two digital-to-frequency converters (DFCs) are used to generate

the pulse outputs. The DFC generates a pulse each time ±1 LSB

is accumulated in the energy register. An output pulse is

generated when CFxDEN number of pulses is generated at the

DFC output.

The CF1 and CF2 pins can be configured to output a signal that

is proportional to the active power, reactive power, apparent

power, or IRMS on Current Channel A or Current Channel B.

In addition, it is possible to configure CF1 and CF2 to output a

signal that is proportional to the sum of the Current Channel A

IRMS and the Current Channel B IRMS, or, alternatively, propor-

tional to the sum of the active power on Current Channel A and

the active power on Current Channel B. Recalibration is required

in this configuration because the actual CF output equals the sum

of the active power on Current Channel A and the active power

on Current Channel B, divided by 2. The CF1 and CF2 output

pins are programmed by setting the CF1SEL and CF2SEL bits

in the CFMODE register (Address 0x107).

Both pulse outputs (CF1 and CF2) are disabled by default

and can be enabled by clearing the CF1DIS and CF2DIS bits,

respectively, in the CFMODE register (Address 0x107).

PULSE OUTPUT CHARACTERISTICS

The pulse outputs for both DFCs stay low for 80 ms if the pulse

period is longer than 160 ms (6.25 Hz). If the pulse period is

shorter than 160 ms, the duty cycle of the pulse outputs is 50%.

The pulse outputs are active low. The maximum output frequency

with ac inputs at full scale and with CFxDEN = 0x00 is approxi-

mately 206.9 kHz.

The ADE7953 includes two unsigned 16-bit registers, CF1DEN

(Address 0x103) and CF2DEN (Address 0x104) that control the

CF output frequency on the CF1 and CF2 pins, respectively. The

16-bit frequency scaling registers can scale the output frequency

by 1/(216 – 1) to 1 with a step of 1/(216 – 1). Note that when

modifying the CF1DEN and CF2DEN registers, two sequential

write operations must be performed to ensure that the write is

successful.

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