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

The INA280 amplifies the voltage developed across a current-sensing resistor as current flows through the

resistor to the load. The wide input common-mode voltage range and high common-mode rejection of the

INA280 allows use over a wide range of voltage rails while still maintaining an accurate current measurement.

8.1.1 RSENSE and Device Gain Selection

The accuracy of any current-sense amplifier is maximized by choosing the current-sense resistor to be as large

as possible. A large sense resistor maximizes the differential input signal for a given amount of current flow and

reduces the error contribution of the offset voltage. However, there are practical limits as to how large the

current-sense resistor can be in a given application because of the resistor size and maximum allowable power

dissipation. Equation 1 gives the maximum value for the current-sense resistor for a given power dissipation

budget:

MAX

SENSE

2

MAX

PD

R

I

(1)

where:

• PDMAX is the maximum allowable power dissipation in RSENSE.

• IMAX is the maximum current that will flow through RSENSE.

An additional limitation on the size of the current-sense resistor and device gain is due to the power-supply

voltage, VS, and device swing-to-rail limitations. To make sure that the current-sense signal is properly passed to

the output, both positive and negative output swing limitations must be examined. Equation 2 provides the

maximum values of RSENSE and GAIN to keep the device from exceeding the positive swing limitation.

I

MAX

ª RSENSE ª *$,1 < VSP

(2)

where:

• IMAX is the maximum current that will flow through RSENSE.

• GAIN is the gain of the current-sense amplifier.

• VSP is the positive output swing as specified in the data sheet.

To avoid positive output swing limitations when selecting the value of RSENSE, there is always a trade-off

between the value of the sense resistor and the gain of the device under consideration. If the sense resistor

selected for the maximum power dissipation is too large, then it is possible to select a lower-gain device in order

to avoid positive swing limitations.

The negative swing limitation places a limit on how small the sense resistor value can be for a given application.

Equation 3 provides the limit on the minimum value of the sense resistor.

I

MIN

ª RSENSE ª *$,1 > VSN

(3)

where:

• IMIN is the minimum current that will flow through RSENSE.

• GAIN is the gain of the current-sense amplifier.

INA280

SBOSA19 – OCTOBER 2020

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