ADE7953 datasheet(21/68 Pages) AD

21 / 68 page

Data Sheet

ADE7953

Rev. A | Page 21 of 68

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

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.

MAGNETIC FIELD CREATED BY CURRENT

(DIRECTLY PROPORTIONAL TO CURRENT)

+ EMF (ELECTROMOTIVE FORCE)

– INDUCED BY CHANGES IN

MAGNETIC FLUX DENSITY (di/dt)

Figure 40. 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

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).

VOLTAGE CHANNEL ADC

Figure 41 shows the ADC signal path and signal processing for

the voltage channel input, which is accessed through the VP and

VN 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 ±500 mV

and a PGA_V gain setting of 1, the ADC produces its maximum

output code. The ADC output swings between −6,500,000 LSBs

(decimal) and +6,500,000 LSBs. Note that this output varies

from part to part.

As shown in Figure 41, there is a high-pass filter (HPF) in the

voltage 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

filters in both current channels and in the voltage channel.

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