Datasheet

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 I
rms
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 V
2
(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.
768,32
2
×+= IRMSOSII
0
rmsrms
(6)
where I
rms0
is the rms measurement without offset correction.
I
rms
(t)
0x00
+
IRMSOS[11:0]
I
rms
[23:0]
2
26
2
25
sgn 2
27
2
17
2
16
2
18
24 24
dt
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
06353-037
HPF
I
P
*NOT AVAILABLE IN THE ADE7566.
Figure 61. ADE7566/ADE7569 Current Channel RMS Signal Processing with PGA1 = 1, 2, 4, 8, or 16