7 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.

7.1 Application Information

The INA791x measures the voltage developed as current flows across the integrated current shunt. The device

provides a reference pin to configure operation as either unidirectional or bidirectional output swing. When

using the INA791x for inline motor current sense or measuring current in an H-bridge, the device is commonly

configured for bidirectional operation.

7.1.1 Calculating Total Error

The INA791x electrical specifications Electrical Characteristics include typical individual errors terms (such as

gain error, offset error, and nonlinearity error). Total error, including all of these individual error components, is

not specified in the table. To accurately calculate the expected error of the device, the user must first know the

device operating conditions. This section discusses the individual error sources and how the device total error

value can be calculated from the combination of these errors for specific conditions.

Three examples are provided in Table 7-1, Table 7-2, and Table 7-3 that detail how different operating conditions

can affect the total error calculations. Typical and maximum calculations are shown as well to provide the user

more information on how much error variance is present from device to device.

7.1.1.1 Error Sources

The typical error sources that have the largest effect on the total error of the device are gain error, nonlinearity,

common-mode rejection ratio, and input offset error. For the INA791x , an additional error source (referred to as

the reference voltage rejection ratio) is also included in the total error value.

7.1.1.2 Reference Voltage Rejection Ratio Error

Reference voltage rejection ratio refers to the amount of error induced by applying a reference voltage to the

INA791x that deviates from the mid-point of the device supply voltage.

7.1.1.3 External Adjustable Gain Error

The INA791x features external adjustable gain with two external resistors as described in Adjustable Gain Set

Using External Resistors. The tolerance of these external resistors contribute to the total gain error of the

system. These resistors are recommended to be of same kind so that temperature drift of these resistor track

closely. Equation 4 can be used for calculating total error contributed by two external gain resistors.

ErrorG_R=  2*ResistorTolerance+Resistordrift×∆ T

(4)

7.1.1.4 Total Error Example 1

Table 7-1. Total Error Calculation: Example 1 (1)

TERM

SYMBOL

EQUATION

MAX VALUE

Initial input offset with

Temp drift

IOS_T

IOS

40mA

Added input offset

because of common-mode

voltage

IOS_CM

CMRR× VCM–48V 

0µA

Added input offset

because of reference

voltage

IOS_REF

RVRR× VS2–VREF 

0µA

INA791A, INA791B

SBOSAD1A – MAY 2024 – REVISED JULY 2025

www.ti.com

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