7.3 Feature Description

7.3.1 Setting the Gain

Figure 7-2 shows that the gain of the INA630 is set by a resistor divider (R1, R2) connected between the output,

feedback, and reference pin.

gm1

gm2

R2

R1

+

–

GND

+

–

VDM/2

VDM/2

1

+

+

+

VOUT

VFB

VREF

VS

VS+

VINN

VINP

+

+

gm3

G = 1 +

R2

R1

Figure 7-2. Simplified Diagram of the INA630 With Gain Equations

The value of R1 and R2 is selected according to:

G=1+R2R1

(1)

Table 7-1 lists several commonly used gains and feedback resistor values. The table also shows the theoretical

gain error that is caused by the worst-case tolerance of available 0.05% resistors, which means that both

resistors have the opposite absolute error.

Table 7-1. Examples for Feedback Resistor Values (0.05%)

DESIRED GAIN

R1 (Ω) (0.05%)

R2 (Ω) (0.05%)

GAIN ERROR (WORST-

CASE) (%)

20

1k

18.88k

0.5

50

1k

49.28k

0.28

80

1k

78.67k

0.23

100

1k

98.81k

0.09

120

1k

118.35k

0.54

150

1k

148.6k

0.24

200

1k

198.1k

0.4

500

1k

498.8k

0.01

1000

1k

1M

0.1

7.3.1.1 Gain Error and Drift

Instrumentation amplifiers can set the gain by a single resistor, whereas in the INA630, the gain and thus the

gain accuracy is determined by the relative match of the external feedback resistor network R1 and R2.

An advantage of this configuration becomes evident for temperature drifts. In traditional instrumentation

amplifiers, the external resistor must match the internal monolithic resistors. Discrete resistors are available

with a ratio temperature coefficient of < 10ppm/°C to achieve excellent gain drift performance.

INA630

SBOSAI8 – MARCH 2025

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