MIN

SENSE

SN

I

R

GAIN > V

u

u

MAX

SENSE

SP

I

R

GAIN

V

u

u

MAX

SENSE

2

MAX

PD

R

I

11

INA191

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SLYS020 – FEBRUARY 2019

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Application Information (continued)

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:

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)