8.1.3 Signal Conditioning

When performing accurate current measurements in noisy environments, the current-sensing signal is often

filtered. The INAx191 features low input bias currents. Therefore, it is possible to add a differential mode filter

to the input without sacrificing the current-sense accuracy. Filtering at the input is advantageous because this

action attenuates differential noise before the signal is amplified. Figure 8-2 provides an example of how to use a

filter on the input pins of the device.

VOUT

VS

1.7 V to 5.5 V

IN±

IN+

VS

OUT

RF

CF

RF

+

±

Bus Voltage

up to 40 V

RSENSE

Load

Capacitively Coupled

Amplifier

ENABLE

3dB

F F

1

f

4 R C

S

RDIFF

TI Device

Figure 8-2. Filter at the Input Pins

The differential input impedance (RDIFF) shown in Figure 8-2 limits the maximum value for RF. The value of RDIFF

is a function of the device temperature and gain option, as shown in Figure 8-3.

Temperature (qC)

-50

-25

0

25

50

75

100

125

150

1

1.5

2

2.5

3

3.5

4

A1

A2, A3, A4, A5

Figure 8-3. Differential Input Impedance vs. Temperature

INA191, INA2191

SLYS020C – FEBRUARY 2019 – REVISED AUGUST 2021

www.ti.com

24

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