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BQ40Z80: CELL BALANCE TIME CALCULATION

Shubham Yadav
Intellectual 285 points
Part Number: BQ40Z80

Dear Sir,

In our BMS, we have configured default values of cell balancing time as specified in TRM. As we are using a series resistor of 100 ohm, I have recalculated cell balancing time and want to verify it from you. Whether am I  doing calculation correctly or using proper parameters value. I have appended below my calculations please have a look in to it and also please give suggestions how I can achieve faster cell balancing.




VCELL= 3600 mv (I had taken here nominal cell volatge as specified in cell datasheet)  Is it correct ?
RVCx= 100 ohm
Rcb (these i can get as we are using internal cell balancing so no fet i can see in series with cell so i have taken it as)= 0
Duty cycle =75%

According to formulas,

Balance time per mAh for cell 1= 133 s/mAh

Balance time per mAh for cell 2-6 = 267 s/mAh

Please verify if above values are correct.... and how cell balancing will behave after i changed to these values.

Regards,
Shubham

  • 0
    TI__Mastermind 25136 points

    Hello Shubham,

    The cell balancing calculations is more difficult than what the TRM shows. The firmware does other things which I briefly talked about in this Thread. 

    Please refer to this app note to learn more about how cell balancing works. 

    To achieve FAST balancing, you probably will need external circuitry. PLease refer to this app note.

    Regards,
    Jose Couso