ADE7758ARWRL datasheet(21/68 Pages) AD

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ADE7758

Rev. A | Page 21 of 68

di/dt CURRENT SENSOR AND DIGITAL

INTEGRATOR

The di/dt sensor detects changes in the magnetic field caused by

the ac current. Figure 42 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 42. 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. The

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 needs to 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 ADE7758 has a built-

in digital integrator to recover the current signal from the di/dt

sensor. The digital integrator on Channel 1 is switched on by

default when the ADE7758 is powered up. Setting the MSB of

the GAIN[7:0] register turns on the integrator. Figure 43 to

Figure 46 show the magnitude and phase response of the digital

integrator.

100

10k

–50

–40

–30

–20

–10

FREQUENCY (Hz)

Figure 43. Combined Gain Response of the

Digital Integrator and Phase Compensator

100

10k

FREQUENCY (Hz)

Figure 44. Combined Phase Response of the

Digital Integrator and Phase Compensator

–1

FREQUENCY (Hz)

Figure 45. Combined Gain Response of the

Digital Integrator and Phase Compensator (40 Hz to 70 Hz)

89.80

90.10

90.05

90.00

89.95

89.90

89.85

FREQUENCY (Hz)

Figure 46. Combined Phase Response of the

Digital Integrator and Phase Compensator (40 Hz to 70 Hz)

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