+

20 k

380 k

380 k

380 k

19 k

−15 V

1 F

15 V

1 F

GND

4

7

2

3

1

6

5

−IN

+IN

100 nF

100 nF

+

20 k

380 k

380 k

380 k

19 k

30 V

1 F

GND

4

7

2

3

1

6

5

−IN

+IN

100 nF

INA149

www.ti.com

SBOS579A

– SEPTEMBER 2011 – REVISED NOVEMBER 2011

APPLICATION INFORMATION

BASIC INFORMATION

Figure 43 shows the basic connections required for dual-supply operation. Applications with noisy or

high-impedance power-supply lines may require decoupling capacitors placed close to the device pins. The

output voltage is equal to the differential input voltage between pins 2 and 3. The common-mode input voltage is

rejected. Figure 44 shows the basic connections required for single-supply operation.

Figure 43. Basic Power and Signal Connections for Figure 44. Basic Power and Signal Connections for

Dual-Supply Operation

Single-Supply Operation

TRANSFER FUNCTION

Most applications use the INA149 as a simple unity-gain difference amplifier. The transfer function is given in

Equation 1:

(1)

function is given in Equation 2:

(2)

COMMON-MODE RANGE

The high common-mode range of the INA149 is achieved by dividing down the input signal with a high precision

resistor divider. This resistor divider brings both the positive input and the negative input within the input range of

the internal operational amplifier. This input range depends on the supply voltage of the INA149.

Both Figure 2 and Figure 3 can be used to determine the maximum common-mode range for a specific supply

voltage. The maximum common-mode range can also be calculated by ensuring that both the positive and the

negative input of the internal amplifier are within 1.5 V of the supply voltage.

In case the voltage at the inputs of the internal amplifier exceeds the supply voltage, the internal ESD diodes

start conducting current. This current must be limited to 10 mA to make sure not to exceed the absolute

maximum ratings for the device.

Copyright

© 2011, Texas Instruments Incorporated

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