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BQ79718-Q1: BQ79718 External Balance

korcan tuna
Prodigy 180 points
Part Number: BQ79718-Q1

Dear Supporter,

Could you help me about Cell Balancing with External FETs;
Is there any document with selection of Rextr, Qextr, D1, Cgate, Rgate and Rbias? There is no very detailed explanation in the BQ79718-Q1 and BQ79716-Q1 documents. 

Thanks for support,

Best Regards,

  • 0
    TI__Expert 8451 points

    Hello,

    Due to the wide variation in external balancing current desired by customers, we do not have a dedicated value for each component.  What external balancing current are you hoping to achieve with the BQ79718?

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 180 points

    Dear Andria,

    I want to aim minimum 1A external balancing current with BQ79718.

    BR,

    KT

  • +1 in reply to korcan tuna
    TI__Expert 8451 points

    Hi,

    We are currently working to develop an external cell balancing board for the BQ79718.  The board has not been finished or tested yet, but I will recommend the following values for now:

    Rbias: 1kOhm

    Ccb: 4.7 nF

    Rgate: 2kOhm

    Rexbal: adjust to fit cell voltage and FET Rdson

    • Rexbal + Rdson = Vcell / 1 A

    Cgate: 47 nF

    Additionally, we recommend using a zener diode instead of a regular diode from gate to source of the FET.  Please be sure to complete your own testing to ensure these values will work for your application.

    Best,

    Andria