8.2.1.2.1 Input Filter Design

TI recommends placing an RC filter in front of the isolated amplifier to improve signal-to-noise performance of

the signal path. Design the input filter such that:

• The cutoff frequency of the filter is at least one order of magnitude lower than the sampling frequency (fCLKIN)

of the internal ΔΣ modulator

• The DC impedance of the filter does not generate significant voltage drop in the analog input lines

• The source impedance of the analog inputs are equal

Most voltage-sensing applications use high-impedance resistive dividers in front of the isolated amplifier to scale

down the input voltage. In this case, a single capacitor (as shown in Figure 8-2) is sufficient to filter the input

signal.

1 nF

DCDC_OUT

DCDC_HGND

HLDO_IN

HLDO_OUT

HGND

INP

INN

NC

AMC3336

DCDC_IN

LDO_OUT

VDD

DOUT

CLKIN

GND

DIAG

DCDC_GND

Figure 8-2. Input Filter

8.2.1.2.2 Bitstream Filtering

For modulator output bitstream filtering, a device from TI's C2000™ or Sitara™ microcontroller families is

recommended. These families support up to eight channels of dedicated hardwired filter structures that

significantly simplify system level design by offering two filtering paths per channel: one providing high-accuracy

results for the control loop and one fast-response path for overcurrent detection.

A delta-sigma modulator filter calculator is available for download at www.ti.com that aids in the filter design and

selecting the right OSR and filter-order to achieve the desired output resolution and filter response time.

AMC3336

SBASA70 – APRIL 2021

www.ti.com

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