RG

Also drawn in simplified form:

INA128

Ref

VO

VIN

VIN

+

−

G

1

50k

R

G

G

1

49.4k

R

G

INA128:

INA129:

DESIRED

R

NEAREST

R

NEAREST

G

G

GAIN (V/V)

(Ω)

(Ω)

1

NC

NC

NC

NC

2

50.00k

49.9k

49.4k

49.9k

5

12.50k

12.4k

12.35k

12.4k

10

5.556k

5.62k

5489

5.49k

20

2.632k

2.61k

2600

2.61k

50

1.02k

1.02k

1008

1k

100

505.1

511

499

499

200

251.3

249

248

249

500

100.2

100

99

100

1000

50.05

49.9

49.5

49.9

2000

25.01

24.9

24.7

24.9

5000

10.00

10

9.88

9.76

10000

5.001

4.99

4.94

4.87

INA128

INA129

NC: No Connection

A

1

6

7

4

3

8

1

2

V

IN

V+

INA128, INA129

+

5

Over−Voltage

Protection

Over−Voltage

Protection

Load

+

O

V

Ref

NOTE: (1) INA129: 24.7kΩ

−

0.1µF

0.1µF

V−

−

25kΩ(1)

25kΩ(1)

40kΩ

40kΩ

40kΩ

40kΩ

V

(V

+

−

•

)

INA128, INA129

www.ti.com

SBOS051C – OCTOBER 1995 – REVISED OCTOBER 2015

8 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.

8.1 Application Information

The INA12x measures small differential voltage with high common-mode voltage developed between the

noninverting and inverting input. The high-input voltage protection circuit in conjunction with high input

impedance make the INA12x suitable for a wide range of applications. The ability to set the reference pin to

adjust the functionality of the output signal offers additional flexibility that is practical for multiple configurations.

8.2 Typical Application

Figure 24 shows the basic connections required for operation of the INA12x. 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 resistance of 8

Ω in series with the Ref pin will cause a

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

Figure 24. Basic Connections

8.2.1 Design Requirements

The device can be configured to monitor the input differential voltage when the gain of the input signal is set by

output is referenced to ground when no input signal is present by connecting the Ref pin to ground, as Figure 24

shows. When the input signal increases, the output voltage at the OUT pin increases, too.

Copyright © 1995–2015, Texas Instruments Incorporated

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