RG

Also drawn in simplified form:

INA1 28

Ref

VO

VIN

VIN

+

INA128:

INA129:

INA128

INA129

NC: No Connection

A

1

A

2

A

3

6

7

4

3

8

1

2

V

IN

VIN

RG

V+

INA128, INA129

+

5

Over Voltage

Protection

Over Voltage

Protection

Load

+

O

V

Ref

NOTE: (1) INA129: 24.7kW

0.1mF

0.1mF

V

25kW(1)

25kW(1)

40k

40kW

W

40k

40k

W

W

49.4 kW

R

G

G = 1 +

50 kW

R

G

G = 1 +

1

2

5

10

20

50

100

200

500

1000

2000

5000

10000

NC

49.4K

12.35K

5489

2600

1008

499

248

99

49.5

24.7

9.88

4.94

NC

49.9K

12.4K

5.49K

2.61K

1K

499

249

100

49.9

24.9

9.76

4.87

NC

50K

12.5K

5.556K

2.632K

1.02K

505.1

251.3

100.2

50.5

25.01

10

5.001

NC

49.9K

12.4K

5.62K

2.61K

1.02K

511

249

100

49.9

24.9

10

4.99

DESIRED

GAIN (V/V)

R

( )

W

G

NEAREST

1% R ( )

W

G

R

( )

W

G

NEAREST

1% R ( )

W

G

V

O = G

(V

- V )

·

IN

IN

-

+

INA128-HT, INA129-HT

SBOS501F – JANUARY 2010 – REVISED FEBRUARY 2015

www.ti.com

9 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.

9.1 Application Information

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

inverting 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.

9.2 Typical Application

Figure 20 shows the basic connections required for operation of the INA128-HT and INA129-HT. 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) pin that 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.

Figure 20. Basic Connections

9.2.1 Design Requirements

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

the external resistor RG. The output signal references to the Ref pin. The most common application is where the

output is referenced to ground when no input signal is present by connecting the Ref pin to ground, as Figure 20

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

16

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