8 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

8.1.1 Reference Pin

In traditional 3-op amp instrumentation amplifier, the output voltage is developed with respect to the voltage

on the reference pin (REF). Often in dual-supply operation, this reference pin connects to the low-impedance

system ground so any additional impedance at the reference pin degrades the CMRR and gain accuracy.

Impedance on the INA630 reference pin does not affect the CMRR due to the architecture.

However, gain accuracy can be affected by impedance on the reference pin (see Equation 2):

G = 1 + R2+RREFR1  

(2)

+IN

-IN

+V

OUT

-V

INA630

R1

R2

INP

INN

R

REF

+

–

VREF

Figure 8-1. Effect of Reference Pin Impedance on Gain Accuracy

To ensure negligible effect of the reference pin impedance on the gain accuracy (<0.001%), keep:

• Reference impedance < 0.2Ω for G = 20V/V, R1 = 1kΩ

• Reference impedance < 1Ω for G = 100V/V, R1 = 1kΩ

Voltage reference devices can provide low-impedance voltage sources for the reference pin.

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