ADE5166 datasheet(52/148 Pages) AD

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ADE5166/ADE5169/ADE5566/ADE5569

Preliminary Technical Data

Rev. PrB | Page 52 of 148

Current Channel RMS Calculation

Each ADE5166/ADE5169/ADE5566/ADE5569 simultaneously

calculates the rms values for the current and voltage channels in

different registers. Figure 39 and Figure 40 show the detail of the

signal processing chain for the rms calculation on the current

channel. The current channel rms value is processed from the

samples used in the current channel waveform sampling mode

and is stored in an unsigned 24-bit register (Irms). One LSB of

the current channel rms register is equivalent to one LSB of a

current channel waveform sample.

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 in the MODE2 register (0x0C).

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. The current rms measurement provided in the

ADE5166/ADE5169/ADE5566/ADE5569 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 exter-

nally in the microprocessor using an amps/LSB constant.

Current Channel RMS Offset Compensation

The ADE5166/ADE5169/ADE5566/ADE5569 incorporate a

current channel rms offset compensation 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).

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.

32768

IRMSOS

rms

(4)

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

HPF

MODE1[5]

HPF

CURRENT CHANNEL

WAVEFORM

DATA RANGE WITH

INTEGRATOR OFF

0xD70A3E

0x000000

0x28F5C2

60Hz

0xD487B0

IPB

0x2B7850

0x000000

CURRENT CHANNEL

WAVEFORM

DATA RANGE WITH

INTEGRATOR ON (60Hz)

HPF1

DIGITAL

INTEGRATOR*

LPF3

NOTES:

1. WHEN DIGITAL INTEGRATOR IS ENABLED, FULL-SCALE OUTPUT DATA IS ATTENUATED DEPENDING ON THE SIGNAL

FREQUENCY BECAUSE THE INTEGRATOR HAS A –20dB/DECADE FREQUENCY RESPONSE. WHEN DISABLED, THE

OUTPUT IS NOT FURTHER ATTENUATED.

Figure 39. ADE5566/ADE5569 Current Channel RMS Signal Processing with PGA1 = 1, 2, 4, 8, or 16

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