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BQ76930: Passive cell balancing with external N-CH MOSFET

Chetan Bodar1
Prodigy 60 points
Part Number: BQ76930
Other Parts Discussed in Thread: TIDA-01093

Dear Team,

1. Can I use above circuit for external cell balancing with BQ76930 for 20 series cell (using two BQ76930 as per TIDA-01093)?

2. Need explanation how same pin is turning on MOSFET , what will be gate charge voltage when it is turning ON MOSFET during cell balancing.

  • 0
    TI__Guru 54715 points

    Hi Chetan,

    Yes, external balancing could be used with the BQ76930 in a 20 cell implementation similar to TIDA-01093.  An extra consideration with a stacked implementation is that the host will need to watch the voltages of the cells between the 2 groups and balance that group if needed. The host might balance all cells in the higher group in an alternating pattern or run a load specific to that IC for a longer time.

    See http://www.ti.com/lit/pdf/slua749 section 4, particularly figure 6.  The available gate voltage will be about 1/2 of the cell voltage.

  • 0 in reply to WM5295
    Prodigy 60 points

    Dear Team,

    Thanks for clarification, I will study SLUA749 in details and get back to you if any further clarifications.

    with reference to TIDA-01093, here they have used P-Channel MOSFET but I wants to use N-Channel MOSFET, can I use N-CH MOSFET , SOT23 Footprint for external cell balancing for 20S, is there any standard part number with SOT23 footprint suitable to this device.

    Thanks & Regards,

    chetan

  • 0 in reply to Chetan Bodar1
    TI__Guru 54715 points

    Hi Chetan,

    FET selection will vary with your requirement.  If you are balancing at 3.6V you may want a different FET than if you are balancing at 4.2V.  Generally you want a FET with a defined on resistance with the gate voltage you will be using.  You might choose to design based on the performance curves in the data sheet, but those are usually typical data.  I don't know of any specific SOT-23 FETs, check with your favorite distributor or FET supplier, they will usually have selection tools based on available parameters.