ade7753 Analog Devices, Inc., ade7753 Datasheet - Page 16

• Manufacturer Part Number: ade7753
• Description: Active And Apparent Energy Metering Ic With Di/dt Sensor Interface
• Manufacturer: Analog Devices, Inc.

ADE7753
availability by going active low. The timing is shown in
Figure 22. The 24-bit waveform samples are transferred
from the ADE7753 one byte (8-bits) at a time, with the most
significant byte shifted out first. The 24-bit data word is right
justified - see ADE7753 Serial Interface.
The interrupt request output IRQ stays low until the interrupt
routine reads the Reset Status register - see ADE7753 Interrupt.
Channel 1 RMS calculation
Root Mean Square (RMS) value of a continuous signal V(t)
is defined as:
For time sampling signals, rms calculation involves squaring
the signal, taking the average and obtaining the square root:
ADE7753 calculates simultaneously the RMS values for
Channel 1 and Channel 2 in different register. Figure 23
shows the detail of the signal processing chain for the RMS
calculation on channel 1. The channel 1 RMS value is
processed from the samples used in the channel 1 waveform
sampling mode. The channel 1 RMS value is stored in an
unsigned 24-bit register (IRMS). One LSB of the channel 1
DOUT
SCLK
DIN
IRQ
0.5V, 0.25V,
0.125V, 62.5mV,
31.3mV, 15.6mV,
*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 WILL NOT BE FURTHER ATTENUATED.
Figure 22 – Waveform sampling Channel 1
0V
V1
V1
Read from WAVEFORM
Analog
Input
Range
0 0 0
V1P
V1N
V
V
rms
rms
01 Hex
PGA1
x1, x2, x4,
x8, x16
GAIN[2:0]
N
T
1
1
PRELIMINARY TECHNICAL DATA
T
0
i
N
Sign
V
1
V
2
D7AE14h
2851ECh
2
t
000000h
Channel 1 DATA - 24 bits
) (
Figure 21 —ADC and signal processing in Channel 1
dt
i
2.42V, 1.21V, 0.6V
REFERENCE
ADC 1
(1)
(2)
ADC Output
word Range
GAIN[4:3]
2851ECh
D7AE14h
000000h
HPF
–16–
Channel 1 (Current Waveform)
Data Range
RMS register is equivalent to one LSB of a channel 1
waveform sample. The update rate of the channel 1 RMS
measurement is CLKIN/4.
Channel 1
With the specified full scale analog input signal of 0.5V, the
ADC will produce an output code which is approximately
±2,642,412d—see Channel 1 ADC. The equivalent RMS val-
ues of a full-scale AC signal is 1,868,467d (1C82B3h).
Channel 1 RMS offset compensation
The ADE7753 incorporates a channel 1 RMS offset compen-
sation register (IRMSOS). This is 12-bit signed registers
which can be used to remove offset in the channel 1 RMS
calculation. An offset may exist in the RMS calculation due
to input noises that are integrated in the DC component of
V
IRMS register to be maintained at zero when no input is
present on channel 1.
1 LSB of the Channel 1 RMS offset are equivalent to 32,768
LSB of the square of the Channel 1 RMS register. Assuming
that the maximum value from the Channel 1 RMS calcula-
tion is 1,868,467d with full scale AC inputs, then 1 LSB of
the channel 1 RMS offset represents 0.46% of measurement
error at -60dB down of full scale.
where I
tion.
I
rms
Current Signal - i(t)
2
2851ECh
D7AE14h
(t). The offset calibration will allow the content of the
INTEGRATOR*
00h
DIGITAL
I
Figure 23 - Channel 1 RMS signal processing
rms
rmso
0
2
HPF
is the RMS measurement without offset correc-
IRMSOS
24
50Hz
60Hz
32768
1EF73Ch
E108C4h
19CE08h
000000h
E631F8h
000000h
LPF3
SIGN 2
CURRENT RMS (IRMS)
CALCULATION
WAVEFORM SAMPLE
REGISTER
ACTIVE AND REACTIVE
POWER CALCULATION
Channel 1 (Current Waveform)
Data Range After integrator (50Hz)
Channel 1 (Current Waveform)
Data Range After Integrator (60Hz)
25
IRMSOS[11:0]
2
26
Σ
2
27
+
2
17
REV. PrF 10/02
2
16
2
15
24
1C82B3h
I rms (t)
IRMS
00h