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INA381-Q1

SLYS041 – MARCH 2020

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Application Information (continued)

8.1.1.1 Select a Current-Sensing Resistor: Example

In this example, the trade-offs involved in selecting a current-sensing resistor are discussed. This example

requires 5% accuracy for detecting a 10-A overcurrent event under 20 µs where only 250 mW is allowable for the

dissipation across the current-sensing resistor at the full-scale current level. Although the maximum power

dissipation is defined as 250 mW, a lower dissipation is preferred to improve system efficiency. Given the total

error budget of 5%, the INA381-Q1 total error is less than 1%. The INA381-Q1 is well suited for this application

because up to 1% of error is available to be attributed to the measurement error of the device under these

conditions.

As shown in Table 2, the maximum value calculated for the current-sensing resistor with these requirements is

2.5 mΩ. Although this value satisfies the maximum power dissipation requirement of 250 mW, headroom is

available from the 2.5% maximum total overcurrent detection error to reduce the value of the current-sensing

resistor and reduce the power dissipation further. Selecting a 1.5-mΩ, current-sensing resistor value offers a

good tradeoff for reducing the power dissipation in this scenario by approximately 40% and still remaining within

the accuracy region.

PARAMETER

EQUATION

VALUE

UNIT

Maximum current

10

A

Maximum allowable power dissipation

250

mW

2

2.5

mΩ

500

µV

Initial offset voltage error

2%

Gain error

1%

Total measurement error

G

2.23%

Allowable current threshold accuracy

5%

Total system overcurrent response time

10

µs

Allowable overcurrent response

20

µs