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BQ29209-Q1: BQ29209-Q1 several cells in parallel

Daria Stepanova
Prodigy 90 points
Part Number: BQ29209-Q1
Other Parts Discussed in Thread: BQ29209

Dear Support team,

Im planning a design for Li-ion battery management unit. In total I would like to have configuration of 2 cells in series and 4 in parallel (each cell mach current is 2A and voltage is 2V) Im thinking about using BQ29209-Q1 for cells balancing. Could you please comment on how would cells behave if I add this chip to design? What would

Thank you!

  • 0
    TI__Expert 7135 points

    Hi Daria,

    The BQ29209-Q1 is an automotive qualified device, if you do not need this certification I would suggest the BQ29209. It is the same device, but at a slightly lower cost.

    As for the cell balancing algorithm, see section 8.1.2 of the datasheet for details. Cell balancing is enabled by configuring the CB_EN pin. It will begin when there is approximately a 30mV imbalance between the two cells. A load current is applied to the lower voltage cell until both of the cells are approximately the same voltage. Cell balancing will stop until the cells differ by approximately 30mV again.The BQ29209 can handle up to 15mA of cell balancing current. If faster balancing is required, external cell balancing FETs can be used. 

  • 0 in reply to Shawn Hinkle
    Prodigy 90 points

    Thanks for your reply!

    The question is more what would happen if instead of just 2 cells in series I will have 8 cells (2 in series and 4 in parallel) and each of them would haven over / under voltage / current protection. Can it dis-balance batteries? 

  • 0 in reply to Daria Stepanova
    TI__Expert 7135 points

    Hi Daria,

    First of all, apologies for accidentally clicking "TI thinks resolved" on your post! I meant to hit "reply" :)

    From the protection IC, we see all of those batteries in parallel as one battery. The IC will not be able to balance each individual cell with the cells it is in parallel with.