Datasheet

ADE7763 Data Sheet
Rev. C | Page 22 of 56
×1, ×2, ×4,
×8, ×16
ANALOG
INPUT
RANGE
DIGITAL
INTEGRATOR*
HPF
ADC 1
REFERENCE
2.42V, 1.21V, 0.6V
V1
0V
0.5V, 0.25V,
0.125V, 62.5mV,
31.3mV, 15.6mV,
CHANNEL 1
(CURRENT WAVEFORM)
DATA RANGE
ACTIVE AND REACTIVE
POWER CALCULATION
WAVEFORM SAMPLE
REGISTER
CURRENT RMS (IRMS)
CALCULATION
50Hz
V1P
V1N
PGA1
V1
{GAIN[4:3]}
{GAIN[2:0]}
*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 ATTENUATED FURTHER.
ADC OUTPUT
WORD RANGE
0xD7 AE14
0x0 0000
0x28 51EC
0xD7 AE14
0x00 0000
0x28 51EC
CHANNEL 1
(CURRENT WAVEFORM)
DATA RANGE AFTER
INTEGRATOR (50Hz)
0xEI 08C4
0x00 0000
0x1E F73C
60Hz
CHANNEL 1
(CURRENT WAVEFORM)
DATA RANGE AFTER
INTEGRATOR (60Hz)
0xE6 31F8
0x00 0000
0x19 CE08
04481-A-044
dt
Figure 43. ADC and Signal Processing in Channel 1
Channel 1 Sampling
The waveform samples may be routed to the waveform register
(MODE[14:13] = 1, 0) for the system master (MCU) to read. To
enable waveform sampling mode, set the WSMP bit (Bit 3) in
the interrupt enable register to Logic 1. The active and apparent
power as well as the energy calculation remain uninterrupted
during waveform sampling.
In waveform sampling mode, choose one of four output sample
rates using Bits 11 and 12 of the mode register (WAVSEL 1, 0).
The output sample rate can be 27.9 kSPS, 14 kSPS, 7 kSPS, or
3.5 kSPS—see the Mode Register (0X09) section. The interrupt
request output,
IRQ
, signals a new sample availability by going
active low. The timing is shown in Figure 44. The 24-bit wave-
form samples are transferred from the ADE7763 one byte (eight
bits) at a time, with the most significant byte shifted out first.
The 24-bit data-word is right justified—see the Serial Interface
section. The Channel 1 waveform samples have a settling time
of approximately 150 μs. The interrupt request output
IRQ
stays
low until the interrupt routine reads the reset status register—
see the Interrupts section.
CHANNEL 1 DATA
(24 BITS)
READ FROM WAVEFORM
SIGN
0
IRQ
SCLK
DIN
DOUT
0 0 01 HEX
04481-A-045
Figure 44. Waveform Sampling Channel 1
Channel 1 RMS Calculation
The root mean square (rms) value of a continuous signal I(t) is
defined as
IRMS =
∫
×
T
dttI
T
0
2
)(
1
(2)
For time sampling signals, the rms calculation involves squaring
the signal, taking the average, and obtaining the square root:
IRMS =
∑
=
×
N
i
iI
N
1
2
)(
1
(3)
Figure 45 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 rms
register is equivalent to 1 LSB of a Channel 1 waveform sample.
The update rate of the Channel 1 rms measurement is
CLKIN/4. The channel 1 rms measurement has a settling time
of approximately 876 ms with the integrator off and 1340 ms
with the integrator on.