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BQ20Z655-R1: Issue at -30degC temperature

PRAHLAD Supeda
Expert 6150 points
Part Number: BQ20Z655-R1

Customer is using bq20z655-r1 & facing State of charge problem at -30°C.

 Data regarding the issue of bq20z655-r1, schematc & data flash file are sent over mail. 

  • During negative temperature (-30 C) customer checked the battery SMBus communication with the "Ti bq gas guage evaluation software".
  • "Fuel gauge" was showing 0% though the battery was actually 90%-95% charge. Battery voltage was measured as 8.4 V which was full voltage.
  • At communication tab it was showing: "Communication error".

Customer tried replacing the thermistor with a 10K resistor & repeated the test at -30°/-20°. Then the read temperature at -30°/-20° is coming as room temperature (as expected) but State of charge is still becoming zero suddenly.

 Is there any known issue of bq20z655-r1 at lower temperature ?

Datasheet spec for operating temperature is from -40°.

1563.Data.xlsxDF.GG.zip

  • 0
    TI__Genius 10370 points

    Prahlad,

    The IC itself is spec'ed to work at -40C however most batteries in this situation do not. To work that low the customer would need to use our GCP online RbTweak tool to adjust the temperature profile of the ChemID they are using. 

    While voltage might be at 8.4V at that cold the internal impedance increases so high on the battery that once a load is applied your voltage would fall immediately below termination voltage. which means the reporting of 0% capacity is correct. Have they applied a load to see the capacity they truly get? 

    Please use the GPC online chemisty tool and repeat the test. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 40 points

    Dear Eric,

    We have checked with load connected. In this case the load is Handheld Tablet Computer (Our Product) .That tablet has a power consumption of 12 W. In that cold condition battery is able to feed power to the load for 4 Hrs consistent. So it can be concluded that battery power otput is ok. Though the battery actually has power inside the status is showing "0%". when we have checked with external tool to monitor the SMBus line of the battery; it showed communication error.

    Please support us with your valuable suggestion.Anything to be done in Schematic; please let us know.

    Regards

    Arijit

  • 0 in reply to ARIJIT PODDAR
    TI__Genius 10370 points

    Arijit,

    This is not a schematic issue as much as an algorithm issue. At that cold temperatures it is really hard to gauge batteries. You will need to perform an RBTweak to have a chance at those kinds of temperatures. Please Use TI's online GPC tool.

    Thanks,

    Eric Vos