Other Parts Discussed in Thread: INA225
Tool/software:
Product: Texas Instruments INA225
Application: Current sensing in a switching application
Shunt Resistor: 300 mΩ
Bus Voltage: 12 V
Gain Configuration: 100 V/V (Gain set via gain-select pins)
Description of the Issue:
I'm using the INA225 to measure current in a low-side switching application. The setup involves a 300 mΩ shunt resistor and a 12 V system. The INA225 output is fed to an ADC of a microcontroller for current measurement.
The issue arises when the MOSFET is switched on with no load connected (i.e., 0 A current). Ideally, I expect the INA225 output to be 0 mV, but instead I observe:
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At 0 A: Output is ~26 mV (ADC reading), which translates to ~0.8 A false current.
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At 1 A: Output is ~30 mV.
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Beyond 1 A: The INA225 output is accurate and behaves as expected across the entire load range.
Questions:
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What could be the cause of this unexpected offset (~26 mV) at 0 A?
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Is this within the expected input offset voltage + gain error for the INA225?
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Are there specific PCB layout or input biasing considerations that may be contributing to this behavior?
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Should I consider implementing output offset compensation in firmware or using external components?
Additional Notes:
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Power supply to INA225 is stable at 3.3 V.
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No load is connected during the 0 A test.
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The system has fast switching transients due to MOSFET operation.
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The same circuit performs accurately under load.
Any guidance on mitigating or compensating for this offset in the 0–1 A range would be greatly appreciated.
