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Linux/INA226: Current measurement with large offset(250mA)

Yi Yuan
Prodigy 20 points
Part Number: INA226

Tool/software: Linux

Hi Team, I used INA226 as common field current monitor(range as DC 0 - 1.5A). But the MCU get the value of current is 1020mA, But the Multi-Meter current test show 770mA. There is about 250mA offset.

Is there any incorrect design in my .sch

 

  • 0
    TI__Mastermind 27410 points

    Hi Yi,

    The schematic looks alright. Answers to the following questions may help in the debug process:

    What is the value of the sense resistor?

    Is the INA measurement repeatable?

    Is VBUS measurement accurate?

    Is the current constant? If not, you really can’t correlate with a DMM.

    What is the configuration register setting? Have you tried to change conversion time and/or averaging and see if measurement changes?

    Regard, Guang

  • 0 in reply to Guang Zhou
    Prodigy 20 points
    Hello Guang,
    Thanks for your reply. Answer as below:

    What is the value of the sense resistor?
    A: the sense resistor is 50m OHM.

    And we had found the key. As the IT application design, the sense resister is 5m OHM. Our design is 50m OHM.
    For 50m OHM, the R152 and R162 value 10 ohm is real small. there will be a small a leakage current get though the R152 and R162.
    That will add 10mV with the voltage on sense resister. So when the Voltage on sense resister is 37mV, the difference voltage on INA226 will be 47mV. Result as the calculator current is bigger than the real current value on the Sensor resister.

    Now we change the two serial resisters R152 and R162 form 10 OHM to 2.2K OHM. the current value tested OK.
    Regards
    York