V+

R

S

4

3

3

4

+5V

+5V

+5V

REF

OUT

BUF

IN

BUF

OUT

5

5

Digital

I/O

REF

BUF

INA138

1

2

INA138

2

1

MUX

PGIA

12-Bit A/D

Converter

RL

25kΩ

A/D converter programmed for differential input.

RL

25kΩ

Clock

Divider

Oscillator

ADS7870

Serial

I/O

Depending on polarity of current, one INA138 provides

an output voltage, the output of the other is zero.

Time

Load Current

Output

Sign

16

INA138, INA168

SBOS122E – DECEMBER 1999 – REVISED DECEMBER 2017

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Product Folder Links: INA138 INA168

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Copyright © 1999–2017, Texas Instruments Incorporated

Typical Applications (continued)

Figure 16. Bipolar Current Measurements Results (arbitrary scale)

8.2.5 Bipolar Current Measurement Using Differential Input of ADC

The INA1x8 devices can be used with an ADC such as the ADS7870 programmed for differential mode

operation. Figure 17 illustrates this configuration. In this configuration the use of two INAs allows for bidirectional

current measurement. Depending upon the polarity of the current, one of the INAs provides an output voltage,

while the other output is zero. In this way the ADC reads the polarity of current directly, without the need for

additional circuitry.

Figure 17. Bipolar Current Measurement Using Differential Input of ADC