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BQ27520-G4: Ra Max Delta

K.Yaita
Guru 29720 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: BQ28Z610, BQ20Z65

Hi Team,

Technical Reference Manual shows the following about Ra Max Delta.
Could you tell me what is the followng "Ra[4] value" (redline)?
-------------------------------------------------------------------



http://www.tij.co.jp/jp/lit/ug/sluua35/sluua35.pdf
-------------------------------------------------------------------

Best Regards,
Yaita

  • 0
    TI__Expert 4065 points
    Hi Yaita,
    Ra[4] refer to the forth value in the battery resistance table (Ra Tables) in the device Data Flash. Ra Max Delta Value is calculated based on Ra[4] value.
    regards,
    Haidar
  • 0 in reply to Haidar Hamoo
    Guru 29720 points

    Hi Haidar-san,

    Thank you for your support.
    Could yout tell me what is occured if Ra Max Delta isn't set to 15% of the Ra[4] value?
    I would like to know if there is difference between setting more than 15% and less than 15%.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Expert 4065 points
    Hi Yaita-san,
    I haven't tested setting Ra Max Delta beyond 15% of Ra[4] but I can tell you why we use Ra[4] to calculate Ra Max Delta. Ra[4] value (grid point) is close to the battery nominal voltage along the OCV profile, so Ra[4] value could be considered as the battery nominal resistance and that's why we would like to limit the deviation in the measured Ra values to 15% of this value, also relatively large measured Ra values indicate that the battery has aged and may needs to be replaced.
    Regards,
    Haidar
  • 0 in reply to Haidar Hamoo
    Guru 29720 points

    Hi Haidar-san,

    Thank you for your comments.
    Is Ra[4] you said the following red part?



    If the answer is yes, how to calculate 15% of Ra[4]? It seems the default value is "-2".

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru* 76230 points
    Hi Yaita,
    Yes, but the resistance table on this gauge is compressed due to space constrains. So you will have to tell us your chem id and we will tell you what the uncompressed value is, then that way you will be able to calculate the 15% value of that.

    Alternatively if you have a device like the bq27742 or the bq28z610 or bq20z65 where the resistance values are not compressed, you could program your chem id and then check the Ra4 in the gauge df and then calculate 15% of that.


    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Guru 29720 points

    Hi Onyx-san,

    Thank you for your support.
    Chem ID is 3117.

    Best Regards,
    Yaita