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BQ76930: 20S BMS imbalance problem with BQ76930x2

jian wu1
Prodigy 50 points
Part Number: BQ76930
Other Parts Discussed in Thread: TLV333, TLV7031

We are designing a 20S BMS with  BQ76930 , and we have a problem: how to balance the power consumption of the upper and bottom battery，except Regout load resistance? 

and in our design the power supply of the MCU comes from the DC-DC buck, that powered by pack.

(P.S.  OPAMP: tlv333, Comparators: tlv7031, Timer： TPL5111DDCR)

  • 0
    TI__Guru 54715 points

    Hi Jian,

    In addition to the small differences in the supply current of the 2 AFEs, from the diagram it looks like you have some additional circuits powered from the bottom AFE so the load will not be the same.  If the difference is small you may be able to run the balancing of all cells longer to equalize the voltages.  If you have a switched load available which has the right load offset you might use that.  For example if the op-amp circuit always draws more current from the AFE-B and the ISO541 always drew more current from AFE-U, you might run the ISO longer to balance the sub-packs.  Otherwise adding a MCU controlled sub-pack balance mechanism might be desired.  Loading REGOUT as you mention will draw current from the top of the connected cell sub-pack (10 cells) to balance down all the cells connected to that AFE.