ADE7569_15 datasheet(60/152 Pages) AD

60 / 152 page

ADE7116/ADE7156/ADE7166/ADE7169/ADE7566/ADE7569

Rev. B | Page 60 of

152

Current Channel RMS Offset Compensation

The update rate of the current channel rms measurement is

4.096 MHz/5. To minimize noise in the reading of the register,

the Irms register can also be configured to update only with the

zero crossing of the voltage input. This configuration is done by

setting the ZXRMS bit (Bit 2) in the MODE2 register (Address

0x0C).

The ADE7116/ADE7156/ADE7166/ADE7169/ADE7566/

ADE7569 incorporate a current channel rms offset compensa-

tion register (IRMSOS). This is a 12-bit signed register that can

be used to remove offset in the current channel rms calculation.

An offset can exist in the rms calculation due to input noises

that are integrated into the dc component of V2(t).

With the different specified full-scale analog input signal PGA1

values, the ADC produces an output code that is approximately

±0d2,147,483 (PGA1 = 1) or ±0d2,684,354 (PGA1 = 2, 4, 8, or 16);

see the Current Channel ADC section. Similarly, the equivalent

rms value of a full-scale ac signal is 0d1,518,499 (0x172BA3) when

PGA = 1 and 0d1,898,124 (0x1CF68C) when PGA1 = 2, 4, 8, or 16.

One LSB of the current channel rms offset is equivalent to

16,384 LSBs of the square of the current channel rms register.

Assuming that the maximum value from the current channel

rms calculation is 0d1,898,124 with full-scale ac inputs, then

1 LSB of the current channel rms offset represents 0.23% of

measurement error at −60 dB down from full scale.

The current rms measurement provided in the ADE7116/

ADE7156/ADE7166/ADE7169/ADE7566/ADE7569 is accurate

to within 0.5% for signal inputs between full scale and full

scale/500. The conversion from the register value to amps must

be done externally in the microprocessor using an amps/LSB

constant.

768

IRMSOS

rms

(6)

where Irms0 is the rms measurement without offset correction.

Irms(t)

0x00

IRMSOS[11:0]

Irms[23:0]

226

225

sgn

227

217 216

218

MODE1[5]

CURRENT CHANNEL

WAVEFORM

DATA RANGE WITH

INTEGRATOR OFF

0xD70A3E

0x000000

0x28F5C2

60Hz

0xD487B0

0x2B7850

0x000000

CURRENT CHANNEL

WAVEFORM

DATA RANGE WITH

INTEGRATOR ON (60Hz)

HPF1

DIGITAL

INTEGRATOR*

LPF3

HPF

*NOT AVAILABLE IN THE ADE7566.

Figure 61. ADE7566/ADE7569 Current Channel RMS Signal Processing with PGA1 = 1, 2, 4, 8, or 16

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