ADE7759_15 datasheet(13/36 Pages) AD

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REV. A

ADE7759

–13–

FREQUENCY – Hz

101

–10

–20

–30

–40

–50

–60

102

103

104

Figure 10. Gain Response of the Digital Integrator

FREQUENCY – Hz

–88.0

101

–88.5

–89.0

–89.5

–90.0

–90.5

–91.0

–91.5

–92.0

102

103

104

Figure 11. Phase Response of the Digital Integrator

FREQUENCY – Hz

–6

–1

–2

–3

–4

–5

Figure 12. Gain Response of the Digital Integrator

(40 Hz to 70 Hz)

–90.020

–89.985

–89.990

–89.995

–90.000

–90.005

–90.010

FREQUENCY – Hz

–90.015

–89.980

Figure 13. Phase Response of the Digital Integrator

(40 Hz to 70 Hz)

Note that the integrator has a –20 dB/dec attenuation and

approximately –90

° phase shift. When combined with a di/dt

sensor, the resulting magnitude and phase response should be a

flat gain over the frequency band of interest. However, the di/dt

sensor has a 20 dB/dec gain associated with it, and generates

significant high frequency noise. A more effective antialiasing

filter is needed to avoid noise due to aliasing—see Antialias

Filter section.

When the digital integrator is switched off, the ADE7759 can be

used directly with a conventional current sensor such as current

transformer (CT) or a low resistance current shunt.

ZERO CROSSING DETECTION

The ADE7759 has a zero crossing detection circuit on Channel 2.

This zero crossing is used to produce an external zero cross

signal (ZX), and it is also used in the calibration mode—see

Energy Calibration section. The zero crossing signal is also used

to initiate a temperature measurement on the ADE7759—see

Temperature Measurement section. Figure 14 shows how the

zero cross signal is generated from the output of LPF1.

ADC 2

REFERENCE

LPF1

f–3dB = 156Hz

–63% TO +63% FS

PGA2

{GAIN [7:5]}

V2P

V2N

ZERO

CROSS

MULTIPLIER

21.04 @ 60Hz

1.0

0.93

LPF1

Figure 14. Zero Cross Detection on Channel 2

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