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INA232: can not readout small current

?? ?
Prodigy 30 points
Part Number: INA232

System at IDLE mode，bus voltage is 14V,current is around 0.8mA，when do SW readout,power is 0.0128W,Bus voltage is 14.016V,but current is 0A,please find details as below picture,

We did an experiment, adjusting the loading slowly to find out when we can read out non-zero current,and get below result,it seems the min. readout value is 0x0600 equals 1.3mA.Why it can not recognize 1LSB?

BTW,only 1pcs TPS563200DDC is used in this system,should be no harmonics of 500K.

  • 0
    TI__Mastermind 27680 points

    Hi,

    If I’m not mistaken, the equivalent current LSB is 1.25mA. The fact that 1.3mA or larger can be detected is likely due to non-idealities such as offset and noise.

    It is likely that there will be some variation in the value as well.

    Regards, Guang  

  • 0 in reply to Guang Zhou
    Prodigy 30 points

    Sorry, I can't follow you.Current_LSB in our setting is 200uA,what do you mean by saying 'the equivalent current LSB is 1.25mA'? And why we can't readout value less than 0x0600?e.g.0x0100.

  • 0 in reply to ?? ?
    TI__Mastermind 27680 points

    Hi,

    The sense resistor is 2mOhm, Vshunt LSB is 2.5uV. The equivalent current LSB (physically possible) would be 2.5uV/2mOhm=1.25mA.

    Regards, Guang  

  • 0 in reply to Guang Zhou
    Prodigy 30 points

    Hi,

    Thanks for your explanation,I got it.Then another question came into my mind,in our IDLE mode measurement,the actual current is 0.8mA，current by SW readout is 0A which is reasonable ,but the power by SW readout is 0.0128W which almost followed the actual value,Why doesn't it read 0?

  • +1 in reply to ?? ?
    TI__Mastermind 27680 points

    Hi,

    I suppose averaging is enabled? Also power is always positive and it is calculated after each measurement cycle (current, bus voltage).

    Due to noise, it is possible for current to average zero, but power only adds and averages regardless the sign of current.

    Regards, Guang