ade7566 Analog Devices, Inc., ade7566 Datasheet - Page 49

• Manufacturer Part Number: ade7566
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

Current Channel RMS Calculation
Each ADE7566/ADE7569 simultaneously calculates the rms values
for the current and voltage channels in different registers. Figure 56
shows 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 (I
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 I
zero crossing of the voltage input. This configuration is done by
setting the ZXRMS bit in the MODE2 register (0x0C).
With the specified full-scale analog input signal different 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 for the
equivalent rms value of a full-scale ac signal is 0d1,518,499
(0x172BA3) when PGA = 1 and 0d1,898,124 (0x1CF68C) when
rms
register can also be configured to update only with the
rms
). One LSB of the current channel rms register is
IB
IA
HPF
HPF
Figure 56. Current Channel RMS Signal Processing with PGA1 = 2, 4, 8, or 16
INTEGRATOR*
MODE1[5]
DIGITAL
dt
HPF1
0xD70A3E
0xD487B0
0x2B7850
0x28F5C2
0x000000
0x000000
Rev. 0 | Page 49 of 136
60Hz
24
CURRENT CHANNEL
WAVEFORM
DATA RANGE WITH
INTEGRATOR ON (60Hz)
CURRENT CHANNEL
WAVEFORM
DATA RANGE WITH
INTEGRATOR OFF
PGA1 = 2, 4, 8, or 16. The current rms measurement provided
in the 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.
Current Channel RMS Offset Compensation
The ADE7566/ADE7569 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 in the dc component of V
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 of full scale.
where I
I
rms
LPF3
sgn
rms0
=
2
is the rms measurement without offset correction.
25
I
2
26
rms
IRMSOS[11:0]
2
27
0
2
+
+
2
IRMSOS
18
2
17
2
16
24
×
32768
ADE7566/ADE7569
0x00
I
rms
I
rms
(t)
[23:0]
2
(t).
(4)