Output Offset =

b) Using current source.

INA138-Q1

INA138-Q1

V

IN+

V

IN–

OUT

V

IN+

V

IN–

OUT

Copyright © 2016, Texas Instruments Incorporated

R

1

R

2

V

O

R

L

V

O

100 A

μ

Gain Set by R

R

||

1

2

(V )R

R

2

R + R

1

2

a) Using resistor divider.

Gain Set by R

L

Output Offset = (100 A)(R )

μ

L

(independent of V+)

V

R

15

INA138-Q1, INA168-Q1

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SGLS174J – SEPTEMBER 2003 – REVISED AUGUST 2018

Product Folder Links: INA138-Q1 INA168-Q1

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8.2.3 Offsetting the Output Voltage

For many applications using only a single power supply, the output voltage may have to be level shifted away

from ground when there is no load current flowing in the shunt resistor. Level shifting the output of the INA1x8-

Q1 is easily accomplished by one of two simple methods shown in Figure 14. Method (a) on the left-hand side of

Figure 14 shows a simple voltage-divider method. This method is useful for applications that require the output of

the INA1x8-Q1 to remain centered with respect to the power supply at zero load current through the shunt

resistor. Using this method, the gain is determined by the parallel combination of R1 and R2, while the output

offset is determined by the voltage divider ratio of R1 and R2, as shown in Figure 14(a). For applications that

require a fixed value of output offset independent of the power-supply voltage, use current-source method (b)

shown on the right-hand side of Figure 14. With this method, a REF200 constant current source is used to

generate a constant output offset. Using this method, the gain is determined by RL, and the offset is determined

by the product of the value of the current source and RL.

Figure 14. Offsetting the Output Voltage

8.2.4 Bipolar Current Measurement

Configure the INA1x8-Q1 as illustrated in Figure 15 for applications where bidirectional current measurement is

required. Two INA1x8-Q1 devices are required; connect the inputs across the shunt resistor; see Figure 15. A

comparator, such as the TLV3201, is used to detect the polarity of the load current. The magnitude of the load

current is monitored across the resistor connected between ground and the connection labeled Output. In this

example, the 100-kΩ resistor results in a gain of 20 V/V. The 10-kΩ resistors connected in series with the

INA1x8-Q1 output current are used to develop a voltage across the comparator inputs. Two diodes are required

to prevent current flow into the INA1x8-Q1 output because only one device at a time provides current to the

Output connection of the circuit. The circuit functionality is illustrated in Figure 16.