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BQ76930: Smallest charge current detectable with BQ76930

John Whelan
Prodigy 10 points
Part Number: BQ76930

Tool/software:

Hi,

What is the smallest charge and discharge current that the BQ76930 can detect? I'm trying to detect mA signals but also a large scale 30A peak current.

Can Rsns be set to say measure 3mA to 30A, using <6mR?

  • 0
    TI__Mastermind 42060 points

    Hello John,

    The BQ76930 has a current LSB of 8.44-uV:

    With a 6-mOhm, this would correspond to ~1.407-mA of resolution. 30-A should also be within the range of the -200-mV to 200-mV of the CC ADC. 

    So to me it sounds like you should be able to measure 3-mA to 30-A of currents with the BQ76930.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hi Luis,

    But is the accuracy of the BQ76930 sufficient to actually detect 1.407mA?

    Best regards,

    John

  • 0 in reply to John Whelan
    TI__Mastermind 42060 points

    Hello John,

    Resolution would be ~1.407mA, so current measurements would essentially be in steps of that amount. There may be some LSB errors associated to the coulomb counting ADC itself at different voltage ranges.

    When it is close to no current on the sense resistor the predominant error would likely be offset error, this means that you may see current jumping between 0 and +/- 1.407mA. 

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hi Luis,

    Many thanks again.

    Would I be right in thinking set Rsns to give accurate readings for 3mA and at 30A just allow the CC ADC to overflow? i.e. out of range flag (we don't care about measuring 30A consumption as it is very low duty cycle) but then we have issues with OCD and SCD?

    Back to the drawing board.

    Best regards,

    John

  • 0 in reply to John Whelan
    TI__Mastermind 42060 points

    Hello John,

    That is probably okay. The BQ76930 uses analog comparators for the OCD/SCD protections, so it is independent from the ADC measurement. You may want to check what are the settings for the OCD/SCD protections to see what makes the most sense for you.

    If you do not care about the CC accuracy at the higher voltages, the full-scale range of the CC ADC is actually 270-mV, after that point it may begin to overflow. After that point, you just have to make sure to not exceed the ABS max of the pins, which is -0.3-V to 3.6-V (with respect to Vss). So it should be okay to let it overflow if you desire it.

    Best Regards,

    Luis Hernandez Salomon