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Effective Current in bq27621

AntonNadezhdin
Intellectual 420 points

Hi TI,

I have the question about Effective Current calculations in the bq27621 fuel gauge. I have the standard 4.2V Li-pol battery with 40 mAh capacity. I configured the gauge capacity and energy with the 10-x multiplier. The gauge successfully measured the SOC and the remaining capacity, which is 10x of the real battery capacity, but Effective Current and Average Power reading from the gauge is always zero (when real current is about 1-2mA). This leads to the fact that the gauge is always in Sleep mode. Maybe I do something wrong?

This leads to the fact that the system is

  • 0
    TI__Genius 14985 points
    The bq27621 relies on a changing voltage to estimate the current. If your current is so low that there is no relatively quick voltage change then it may not register any current to report. 1-2mA is a fairly light load on your 40mAh battery, so I suspect that is what is happening. There is also a DVC Deadband configuration setting and current below that will be reported as zero. WIth your 10x scaling, 1mA will be reported as 10mA, which is below the default DVC Deadband of 15mA so it will report 0mA in EffectiveCurrent.
    Another possible side effect which you might run into is that as the voltage slowly decreases, the SOC may appear to be stuck and not decreasing. This is because SOC Smoothing is enabled by default and it blocks the RemainingCapacityFiltered( ) value from decreasing unless there is actual discharge current detected. You will notice the RemainingCapacityUnfiltered( ) is decreasing because it is updating based on the slowly dropping voltage (taking OCV measurements). Since SMOOTHEN = 1 by default, the SOC is calculated as RemainingCapacityFiltered( ) / FullChargeCapacityFiltered and this won't be doing down. Changing SMOOTHEN = 0 is recommended for your application to avoid this.
  • 0 in reply to dMax
    Intellectual 420 points

    Thank you for the detailed answer,
    I will change SMOOTHEN parameter to 0 in my project as you recommend.