Output

Device

Load

Supply

ADC

V+

OUT

GND

IN-

IN+

C

BYPASS

0.01 F

m

to

0.1 F

m

2.7 V to 26 V

REF

R

1

R

3

R

2

R

4

R

SHUNT

Copyright © 2017, Texas Instruments Incorporated

19

INA210, INA211, INA212, INA213, INA214, INA215

www.ti.com

SBOS437J – MAY 2008 – REVISED FEBRUARY 2017

Product Folder Links: INA210 INA211 INA212 INA213 INA214 INA215

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Copyright © 2008–2017, Texas Instruments Incorporated

7.4.3 REF Input Impedance Effects

As with any difference amplifier, the INA21x series 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, the

REF pin must be buffered by an op amp.

In systems where the INA21x 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 26 depicts a method of taking the output from the INA21x by using the REF pin as a

reference.

Figure 26. Sensing the INA21x to Cancel the Effects of Impedance on the REF Input

7.4.4 Using The INA21x With Common-Mode Transients Above 26 V

With a small amount of additional circuitry, the INA21x series 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. Start by adding

a pair of resistors as a working impedance for the zener; see Figure 27. 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 Input Filtering 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.