OUT

S

S

L

V

I

R

1000 µA / V R

O

m

IN

IN

I

g

V

V

11

INA139, INA169

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SBOS181F – DECEMBER 2000 – REVISED FEBRUARY 2017

Product Folder Links: INA139 INA169

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Copyright © 2000–2017, Texas Instruments Incorporated

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

8.1.1 Operation

Figure 9 illustrates the basic circuit diagram for both the INA139 and INA169. Load current IS is drawn from

supply VS through shunt resistor RS. The voltage drop in shunt resistor VS is forced across RG1 by the internal

operational amplifier, causing current to flow into the collector of Q1. The external resistor RL converts the output

current to a voltage, VOUT, at the OUT pin.

The transfer function for the INA139 is given by Equation 3:

where

•

gm = 1000 µA/V

(3)

In the circuit of Figure 9, the input voltage (VIN+ – VIN–) is equal to IS × RS and the output voltage(VOUT) is equal

to IO × RL. The transconductance (gm) of the INA139 is 1000 µA/V. The complete transfer function for the current

measurement amplifier in this application is given by Equation 4:

(4)

The maximum differential input voltage for accurate measurements is 0.5 V, which produces a 500-µA output

current. A differential input voltage of up to 2 V will not cause damage. Differential measurements (pins 3 and 4)

must be unipolar with a more-positive voltage applied to pin 3. If a more-negative voltage is applied to pin 3, the

output current, IO, is zero, but it will not cause damage.