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BQ40Z50: the problem of impedance Track，why Load current variation does not Impact on RSOC?

user5141498
Intellectual 380 points
Part Number: BQ40Z50

Hi TI engineer:

              refer to theory and Implementation of Impedance Track™ Battery Fuel-Gauging Algorithm in bq2750x Family

              DODstart = DOD0 + PassedCharge/Qmax     --------  get DODstart

              V(DODx,T) = OCV(DODx,T)+ I×R(DODx,T) by incrementing DOD with dDOD increment of 4%.  --------  get DODfin

              RM = (DODfin-DODstart)×Qmax 

              1. Load current variation   --- lead to --- DODfin   change   ,,,,   so the RM will change frequently,    but why the RSOC looks very stable？

              2.  for Battery that have been studied ， if i remove the cell connect line ，remove the power for bq40z50，  then power it again，  the rsoc is correct also.

               how it know the current   DODstart ?  if PassedCharge  in ram , it already lose.

              thank you very much!

  • 0
    TI__Expert 6575 points
    Hi,
    1. When there is load change, the true FCC and true RM will change, however, it is not so desireable to see jumps in your RSOC during operation, so these are smoothed out. Essentially when DODfin is changed the slope of the RM will be changed such that RSOC will reach 0 when it reaches DODfin.
    2. In the case of a reset or power cycle, the PassedCharge will be cleared, but you will see an update in DOD0 which will give you the new Qstart which is still accurate.
    Regards,
    Swami