ADE7756ARSRL datasheet(19/32 Pages) AD

19 / 32 page

REV. 0

ADE7756

–19–

0 0 0 01 HEX

IRQ

DIN

DOUT

SCLK

SAMPLING RATE

(27.9kSPS, 14kSPS, 7kSPS OR 3.5kSPS)

READ FROM WAVEFORM

CHANNEL 1 DATA – 20 BITS

16 s

SIGN

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.

FREQUENCY – Hz

–40

101

103

102

–60

–40

–20

(60Hz, –21.04 )

(60Hz, –0.6dB)

–80

Figure 20. Magnitude and Phase Response of LPF1

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%.

|( )|

– .









156

093

0 6

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.

–63% TO + 63% FS

60Hz

1V, 0.5V,

0.25V, 0.125V,

0.0625V

x1, x2, x4,

x8, x16

GAIN[7:5]

REFERENCE

2.42V

2851Fh

D7AE1h

+63% FS

–63% FS

+44% FS

–44% FS

00000h

1C396h

E3C6Ah

ANALOG INPUT

RANGE

LPF OUTPUT

WORD RANGE

MULTIPLIER

WAVEFORM

LPF1

V2P

V2N

ADC2

PGA2

40000h

+FS

C0000h

–FS

60Hz

Figure 21. ADC and Signal Processing in Channel 2

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