ADE7756 Ver la hoja de datos (PDF) - Analog Devices
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ADE7756 Datasheet PDF : 32 Pages
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SAMPLING RATE
(27.9kSPS, 14kSPS, 7kSPS OR 3.5kSPS)
IRQ
SCLK
DIN
16s
READ FROM WAVEFORM
0 0 0 01 HEX
DOUT
SIGN
CHANNEL 1 DATA – 20 BITS
Figure 19. Waveform Sampling Channel 1
CHANNEL 2 ADC
Channel 2 Sampling
In Channel 2 waveform sampling mode (MODE[14:13] = 1,1
and WSMP = 1) the ADC output code scaling for Channel 2 is
the same as Channel 1, i.e., the output swings between D7AE1h
(–165,151) and 2851Fh (+165,151)—see ADC Channel 1 sec-
tion. However, before being passed to the Waveform register, the
ADC output is passed through a single-pole, low-pass filter
with a cutoff frequency of 156 Hz. The plots in Figure 20
shows the magnitude and phase response of this filter.
0
0
(60Hz, –0.6dB)
–20
–40
–20
(60Hz, –21.04؇)
–60
–80
101
102
FREQUENCY – Hz
–40
103
Figure 20. Magnitude and Phase Response of LPF1
ADE7756
This has the effect of attenuating the signal. For example, if the
line frequency is 60 Hz, the signal at the output of LPF1 will be
attenuated by 30%.
|H( f )|=
1
= 0.93 = –0.6 dB
1
+
60 Hz
156 Hz
2
Note that LPF1 does not affect the power calculation. The signal
processing chain in Channel 2 is illustrated in Figure 21. Unlike
Channel 1, Channel 2 has only one analog input range (1 V
differential). However, like Channel 1, Channel 2 does have a PGA
with gain selections of 1, 2, 4, 8, and 16. For energy measure-
ment, the output of the ADC is passed directly to the multiplier
and is not filtered. An HPF is not required to remove any dc
offset since it is only required to remove the offset from one chan-
nel to eliminate errors due to offsets in the power calculation.
When in waveform sample mode, one of four output sample
rates can be chosen by using Bits 11 and 12 of the Mode regis-
ter. The available output sample rates are 27.9 kSPS, 14 kSPS,
7 kSPS or 3.5 kSPS—see Mode Register section. The interrupt
request output IRQ signals a new sample availability by going
active low. The timing is the same as that for Channel 1 and is
shown in Figure 19.
x1, x2, x4,
x8, x16
GAIN[7:5]
2.42V
REFERENCE
V2P
V2 V2N
PGA2
V1
1V, 0.5V,
0.25V, 0.125V,
0.0625V
0V
60Hz
ANALOG INPUT
RANGE
ADC2
1 –63% TO + 63% FS TO
LPF1
MULTIPLIER
TO
WAVEFORM
20 REGISTER
40000h
2851Fh
1C396h
LPF OUTPUT
WORD RANGE
+FS
+63% FS
+44% FS
00000h
E3C6Ah
D7AE1h
C0000h
60Hz
–44% FS
–63% FS
–FS
Figure 21. ADC and Signal Processing in Channel 2
REV. 0
–19–
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