MIN

SENSE

SN

I

R

GAIN > V

u

u

MAX

SENSE

S

SP

I

R

GAIN < V

V

u

u

MAX

SENSE

2

MAX

PD

R

I

18

INA180, INA2180

SBOS741A – APRIL 2017 – REVISED AUGUST 2017

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Product Folder Links: INA180 INA2180

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Copyright © 2017, Texas Instruments Incorporated

Application Information (continued)

The accuracy of the INAx180 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. The INAx180 have a typical input bias currents of 80 µA for each input

when operated at a 12-V common-mode voltage input. When large current-sense resistors are used, these bias

currents cause increased offset error and reduced common-mode rejection. Therefore, using current-sense

resistors larger than a few ohms is generally not recommended for applications that require current-monitoring

accuracy. A second common restriction on the value of the current-sense resistor is the maximum allowable

power dissipation that is budgeted for the resistor. Equation 1 gives the maximum value for the current sense

resistor for a given power dissipation budget:

where:

•

•

(1)

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

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

where:

•

•

GAIN is the gain of the current sense-amplifier.

•

•

(2)

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 of a sense resistor can be used in a given application.

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

where:

•

•

GAIN is the gain of the current sense amplifier.

•

(3)