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ADE7763

Rev. A | Page 14 of 56

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR REAL

POWER CALCULATION

FREQUENCY (RAD/S)

IOS × V

VOS × I

VOS × IOS

× I

Figure 25. Effect of Channel Offsets on the Real Power Calculation

The contents of the offset correction registers are 6-bit, sign and

magnitude coded. The weight of the LSB depends on the gain

setting, i.e., 1, 2, 4, 8, or 16. Table 6 shows the correctable offset

span for each of the gain settings and the LSB weight (mV) for

the offset correction registers. The maximum value that can be

written to the offset correction registers is ±31d—see Figure 26.

Figure 26 shows the relationship between the offset correction

gain of 1. To perform an offset adjustment, connect the analog

inputs to AGND; there should be no signal on either Channel 1

or Channel 2. A read from Channel 1 or Channel 2 using the

waveform register indicates the offset in the channel. This offset

can be canceled by writing an equal and opposite offset value to

the Channel 1 offset register, or an equal value to the Channel 2

offset register. The offset correction can be confirmed by

performing another read. Note that when adjusting the offset of

Channel 1, the digital integrator and the HPF should be

disabled.

Table 6. Offset Correction Range—Channels 1 and 2

Gain

Correctable Span

LSB Size

±50 mV

1.61 mV/LSB

±37 mV

1.19 mV/LSB

±30 mV

0.97 mV/LSB

±26 mV

0.84 mV/LSB

±24 mV

0.77 mV/LSB

CH1OS[5:0]

SIGN + 5 BITS

+50mV

OFFSET

ADJUST

0x3F

0x00

0x1F

–50mV

0mV

SIGN + 5 BITS

01,1111b

11,1111b

Figure 26. Channel 1 Offset Correction Range (Gain = 1)

The current and voltage rms offsets can be adjusted with the

IRMSOS and VRMSOS registers—see the Channel 1 RMS Offset

Compensation and Channel 2 RMS Offset Compensation

sections.

di/dt CURRENT SENSOR AND

DIGITAL INTEGRATOR

A di/dt sensor detects changes in magnetic field caused by ac

current. Figure 27 shows the principle of a di/dt current sensor.

MAGNETIC FIELD CREATED BY CURRENT

(DIRECTLY PROPORTIONAL TO CURRENT)

+ EMF (ELECTROMOTIVE FORCE)

– INDUCED BY CHANGES IN

MAGNETIC FLUX DENSITY (di/dt)

Figure 27. Principle of a di/dt Current Sensor

The flux density of a magnetic field induced by a current is

directly proportional to the magnitude of the current. Changes

in the magnetic flux density passing through a conductor loop

generate an electromotive force (EMF) between the two ends of

the loop. The EMF is a voltage signal that is proportional to the

di/dt of the current. The voltage output from the di/dt current

sensor is determined by the mutual inductance between the

current-carrying conductor and the di/dt sensor. The current

signal must be recovered from the di/dt signal before it can be

used. An integrator is therefore necessary to restore the signal to

its original form. The ADE7763 has a built-in digital integrator

to recover the current signal from the di/dt sensor. The digital

integrator on Channel 1 is switched off by default when the

ADE7763 is powered up. Setting the MSB of CH1OS register

turns on the integrator. Figure 28, Figure 29, Figure 30, and

Figure 31 show the magnitude and phase response of the digital

integrator.

FREQUENCY (Hz)

–10

–20

–30

–40

–50

102

103

Figure 28. Combined Gain Response of the

Digital Integrator and Phase Compensator

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