ade7953 Analog Devices, Inc., ade7953 Datasheet - Page 20

• Manufacturer Part Number: ade7953
• Description: Single Phase, Multifunction Metering Ic With Neutral Current Measurement Ade7953
• Manufacturer: Analog Devices, Inc.

ADE7953
CURRENT CHANNEL ADCs
Figure 39 shows the ADC signal path and signal processing for
Current Channel A, which is accessed through the IAP and IAN
pins. The signal path for Current Channel B is identical and is
accessed through the IBP and IBN pins. The ADC output is a
twos complement, 24-bit data-word that is available at a rate of
6.99 kSPS (thousand samples per second). With the specified full-
scale analog input of ±250 mV and a PGA_Ix gain setting of 2,
the ADC produces its maximum output code. The ADC output
swings between −6,500,000 LSBs (decimal) and +6,500,000 LSBs.
This output varies from part to part.
As shown in Figure 39, there is a high-pass filter (HPF) in each
current channel signal path. The HPF is enabled by default and
removes any dc offset in the ADC output. It is highly recom-
mended that this filter be enabled at all times, but it can be
disabled by clearing the HPFEN bit (Bit 2) in the CONFIG
register (Address 0x102). Clearing the HPFEN bit disables the
filters in both current channels and in the voltage channel.
di/dt Current Sensor and Digital Integrator
As shown in Figure 39, the current channel signal path for both
Channel A and Channel B includes an internal digital integrator.
This integrator is disabled by default and is required only when
interfacing with a di/dt sensor, such as a Rogowski coil. When
using either a shunt resistor or a current transformer (CT), this
integrator is not required and should remain disabled.
A di/dt sensor detects changes in the magnetic field caused by
ac current. Figure 40 shows the principle of a di/dt current sensor.
V
IN
IxP
IxN
×22 (FOR IA ONLY)
×1, ×2, ×4, ×8, ×16,
PGA_x BITS
PGA
REFERENCE
ADC
Figure 39. Current Channel ADC and Signal Path
DSP
xIGAIN
Rev. 0 | Page 20 of 68
HPFEN BIT
CONFIG[2]
HPF
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
differential of the current over time (di/dt). The voltage output
from the di/dt 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 ADE7953 has a built-in digital integrator on each current
channel that recovers the current signal from the di/dt sensor.
Both digital integrators are disabled by default. The digital
integrator on Current Channel A is enabled by setting the
INTENA bit (Bit 0) in the CONFIG register (Address 0x102).
The digital integrator on Current Channel B is enabled by setting
the INTENB bit (Bit 1) in the CONFIG register (Address 0x102).
INTEGRATOR
CONFIG[1:0]
INTENx BIT
DIGITAL
Figure 40. Principle of a di/dt Current Sensor
CURRENT PEAK,
OVERCURRENT
DETECTION
CURRENT RMS (IRMS)
CALCULATION
Ix WAVEFORM
SAMPLING REGISTER
ACTIVE AND REACTIVE
POWER CALCULATION
LPF1
MAGNETIC FIELD CREATED BY CURRENT
(DIRECTLY PROPORTIONAL TO CURRENT)
ZX_I DETECTION
+ EMF (ELECTROMOTIVE FORCE)
– INDUCED BY CHANGES IN
MAGNETIC FLUX DENSITY (di/dt)