®

INA131

7

device. Absolute accuracy of the internal values is

±40%.

The nominal gain with an external R

G

resistor can be

calculated by:

G

= 100 + 250 kΩ

R

G

Where: R

Accuracy of the 250k

Ω term is ±40%.

The stability and temperature drift of the external gain

setting resistor, R

gain accuracy and drift can be directly inferred from the

gain equation (1).

NOISE PERFORMANCE

The INA131 provides very low noise in most applications.

For differential source impedances less than 1k

Ω, the

INA103 may provide lower noise. For source impedances

greater than 50k

Ω, the INA111 FET-Input Instrumentation

Amplifier may provide lower noise.

Low frequency noise of the INA131 is approximately

0.4

µVp-p measured from 0.1 to 10Hz. This is approxi-

mately one-tenth the noise of state-of-the-art chopper-stabi-

lized amplifiers.

FIGURE 1. Basic Connections.

(1)

A

1

A

2

A

3

6

25k

Ω

5k

Ω

25k

Ω

5k

Ω

7

4

3

8

1

2

V

IN

V

IN

V+

V–

INA131

–

+

5

Over-Voltage

Protection

25k

Ω

25k

Ω

Over-Voltage

Protection

Load

V

+

–

0.1µF

0.1µF

Pin numbers are

for DIP packages.

+

–

V

O

INA131

Also drawn in simplified form:

V

O

Ref

V

IN

–

V

IN

+

2.63k

Ω

APPLICATION INFORMATION

Figure 1 shows the basic connections required for operation

of the INA131. Applications with noisy or high impedance

power supplies may require decoupling capacitors close to

the device pins as shown.

The output is referred to the output reference (Ref) terminal

which is normally grounded. This must be a low-impedance

connection to assure good common-mode rejection. A resis-

tance of 5

Ω in series with the Ref pin will cause a device

with 110dB CMR to degrade to approximately 106dB CMR.

SETTING THE GAIN

No external resistors are required for G = 100. On-chip

laser-trimmed resistors set the gain, providing excellent gain

accuracy and temperature stability. Gain is distributed be-

tween the input and output stages of the INA131. Bandwidth

is increased by approximately five times (compared to the

INA114 in G = 100). Input common-mode range is also

improved (see “Input Common-Mode Range”).

Although the INA131 is primarily intended for fixed

G = 100 applications, the gain can be increased by connect-

ing an external resistor to the R

are trimmed for precise ratios, not to absolute values, so the

influence of an external resistor will vary from device to