6.4.3 REF Input Impedance Effects

As with any difference amplifier, the INA21x-Q1 common-mode rejection ratio is affected by any impedance

present at the REF input. This concern is not a problem when the REF pin is connected directly to most

references or power supplies. When using resistive dividers from the power supply or a reference voltage, buffer

the REF pin by an op amp.

In systems where the INA21x-Q1 output can be sensed differentially, such as by a differential input analog-to-

digital converter (ADC) or by using two separate ADC inputs, the effects of external impedance on the REF input

can be cancelled. Figure 6-4 shows a method of taking the output from the INA21x-Q1 family of devices by using

the REF pin as a reference.

Output

INA21x-Q1

Load

Supply

ADC

V+

OUT

GND

IN-

IN+

C

BYPASS

0.01 µF

to

0.1 µF

2.7 V to 26 V

REF

R

1

R

3

R

2

R

4

R

SHUNT

Copyright © 2017, Texas Instruments Incorporated

Figure 6-4. Sensing INA21x-Q1 to Cancel Effects of Impedance on the REF Input

6.4.4 Using the INA21x-Q1 with Common-Mode Transients Above 26 V

With a small amount of additional circuitry, the INA21x-Q1 family of devices can be used in circuits subject

to transients higher than 26 V, such as automotive applications. Use only Zener diode or Zener-type transient

absorbers (sometimes referred to as transzorbs)—any other type of transient absorber has an unacceptable time

delay. Begin by adding a pair of resistors as a working impedance for the Zener diode, as shown in Figure 6-5.

Keeping these resistors as small as possible is preferable, typically around 10 Ω. Larger values can be used

with an effect on gain that is discussed in the Section 6.4.1 section. Because this circuit limits only short-term

transients, many applications are satisfied with a 10-Ω resistor along with conventional Zener diodes of the

lowest power rating that can be found. This combination uses the least amount of board space. These diodes

can be found in packages as small as SOT-523 or SOD-523.

INA210-Q1, INA211-Q1, INA212-Q1, INA213-Q1, INA214-Q1, INA215-Q1

SBOS475K – MARCH 2009 – REVISED NOVEMBER 2023

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