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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The INA199 measures the voltage developed across a current-sensing resistor when current passes through it.

The ability to drive the reference pin to adjust the functionality of the output signal offers multiple configurations,

as discussed throughout this section.

8.2 Typical Applications

8.2.1 Unidirectional Operation

CBYPASS

0.1 µF

Power Supply

Load

Output

-

+

IN-

IN+

GND

V+

OUT

REF

Bus Supply

Copyright © 2017, Texas Instruments Incorporated

Figure 8-1. Unidirectional Application Schematic

8.2.1.1 Design Requirements

The device can be configured to monitor current flowing in one direction (unidirectional) or in both directions

(bidirectional) depending on how the REF pin is configured. The most common case is unidirectional where the

output is set to ground when no current is flowing by connecting the REF pin to ground, as shown in Figure 8-1.

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

8.2.1.2 Detailed Design Procedure

The linear range of the output stage is limited in how close the output voltage can approach ground under

zero input conditions. In unidirectional applications where measuring very low input currents is desirable, bias

the REF pin to a convenient value above 50 mV to get the output into the linear range of the device. To limit

common-mode rejection errors, TI recommends buffering the reference voltage connected to the REF pin.

A less frequently-used output biasing method is to connect the REF pin to the supply voltage, V+. This method

results in the output voltage saturating at 200 mV below the supply voltage when no differential input signal is

present. This method is similar to the output saturated low condition with no input signal when the REF pin is

connected to ground. The output voltage in this configuration only responds to negative currents that develop

negative differential input voltage relative to the device IN– pin. Under these conditions, when the differential

INA199

SBOS469H – APRIL 2009 – REVISED OCTOBER 2023

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