Datasheet

ADE7758 Data Sheet
Rev. E | Page 20 of 72
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)
04443-042
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 propor-
tional 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 disabled 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.
10 100 1k 10k
20
–50
–40
–30
–20
–10
0
10
FREQUENCY (Hz)
GAIN (dB)
04443-043
Figure 43. Combined Gain Response of the
Digital Integrator and Phase Compensator
10 100 1k 10k
80
91
90
89
88
87
86
85
84
83
82
81
FREQUENCY (Hz)
PHASE (Degrees)
04443-044
Figure 44. Combined Phase Response of the
Digital Integrator and Phase Compensator
40 706560555045
5
–1
0
1
2
3
4
FREQUENCY (Hz)
MAGNITUDE (dB)
04443-045
Figure 45. Combined Gain Response of the
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)
40 706560555045
89.80
90.10
90.05
90.00
89.95
89.90
89.85
FREQUENCY (Hz)
PHASE (Degrees)
04443-046
Figure 46. Combined Phase Response of the
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)