®

INA114

8

APPLICATION INFORMATION

Figure 1 shows the basic connections required for operation

of the INA114. 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 typical

device to degrade to approximately 80dB CMR (G = 1).

SETTING THE GAIN

Gain of the INA114 is set by connecting a single external

resistor, R

Commonly used gains and resistor values are shown in

Figure 1.

The 50k

Ω term in equation (1) comes from the sum of the

two internal feedback resistors. These are on-chip metal film

resistors which are laser trimmed to accurate absolute val-

FIGURE 1. Basic Connections.

G

= 1 + 50 kΩ

R

G

(1)

DESIRED

R

G

NEAREST 1% R

G

GAIN

(

Ω)(Ω)

1

No Connection

No Connection

2

50.00k

49.9k

5

12.50k

12.4k

10

5.556k

5.62k

20

2.632k

2.61k

50

1.02k

1.02k

100

505.1

511

200

251.3

249

500

100.2

100

1000

50.05

49.9

2000

25.01

24.9

5000

10.00

10

10000

5.001

4.99

ues. The accuracy and temperature coefficient of these

resistors are included in the gain accuracy and drift specifi-

cations of the INA114.

The stability and temperature drift of the external gain

gain accuracy and drift can be directly inferred from the gain

equation (1). Low resistor values required for high gain can

make wiring resistance important. Sockets add to the wiring

resistance which will contribute additional gain error (possi-

bly an unstable gain error) in gains of approximately 100 or

greater.

NOISE PERFORMANCE

The INA114 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 ampli-

fier may provide lower noise.

Low frequency noise of the INA114 is approximately

0.4

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

one-tenth the noise of “low noise” chopper-stabilized ampli-

fiers.

A

1

A

2

A

3

6

25k

Ω

25k

Ω

25k

Ω

25k

Ω

7

4

3

8

1

2

V

IN

V

IN

R

G

V+

V–

INA114

G = 1 +

50k

Ω

R

G

–

+

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

INA114

R

G

Also drawn in simplified form:

V

O

Ref

V

IN

–

V

IN

+