9 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. Customers should validate and test their design

implementation to confirm system functionality.

9.1 Application Information

9.1.1 Reference Pin

The output voltage of the INA849 is developed with respect to the voltage on reference pin REF.

Use the REF pin to offset the output signal to a precise midsupply level. Typically, this offset is 2.5 V in a 5-V

supply environment. To accomplish this level shift, a voltage source must be connected to the REF pin to level-

shift the output so that the INA849 drives a single-supply analog-to-digital converter (ADC).

For dual-supply operation, the reference pin is typically connected to the low-impedance system ground.

The voltage source applied to the reference pin must have a low output impedance. As shown in Figure 9-1, any

creates an imbalance in the four resistors of the internal difference amplifier. This imbalance results in a

degraded common-mode rejection ratio (CMRR). For best performance, keep the source impedance

(represented as R1) to the REF pin below 5 Ω.

+

±

+

±

+

±

5 k

3 k

5 k

5 k

5 k

3 k

íRG

REF

+VS

OUT

+V

S

íVS

íIN

+IN

+RG

R

G

R1

C3

C2

C1

R2

Figure 9-1. Parasitic Resistance Shown at the Reference Pin

Voltage-reference devices are an excellent option for providing a low-impedance voltage source for the

reference pin. However, if a resistor voltage divider generates a reference voltage, the divider must be buffered

by an op amp (as Figure 9-2 shows) to avoid CMRR degradation.

+

±

100 k

100 k

5 V

5 V

í5 V

1 …F

OUT

INA849

REF

+IN

íIN

5 V

OPA320

Figure 9-2. Using an Op Amp to Buffer Reference Voltages

INA849

SBOS945 – NOVEMBER 2020

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