6.3 Feature Description

6.3.1 Setting the Gain

Figure 6-2 shows the basic connections required for operation of the INA122. The output is referred to the output

reference (Ref) pin that is normally grounded.

Use Equation 1 to calculate the gain of the INA122. Set the gain by connecting a single external resistor, RG, to

the INA122 as shown in Figure 6-2.

G = 5 + 200kΩRG

(1)

Table 6-1 shows the commonly used gains and RG resistor values.

The 200kΩ term in Equation 1 comes from the internal metal film resistors which are laser trimmed to accurate

absolute values. The accuracy and temperature coefficient of these resistors are included in the gain accuracy

and drift specifications of the INA122.

The stability and temperature drift of RG also affects gain. The contribution to gain accuracy and drift from RG

can be directly inferred from Equation 1.

-

+

A1

-

+

A2

100k

25k

25k

100k

RG

2

1

8

3

7

6

5

4

VS

IN

+IN

+VS

REF

OUT

VOUT = (V+IN

V IN)×G

G = 5 +

200k

RG

0.1µF

0.1µF

Load

INA122

Figure 6-2. INA122 Basic Connections

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INA122

SBOS069A – OCTOBER 1997 – REVISED DECEMBER 2024

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