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Multiple Lithium Ion Cell Charging

Vic Pasini
Prodigy 10 points
Other Parts Discussed in Thread: BQ78PL114, UCC3895, BQ34Z100, BQ76PL536

I have a customer who is trying to charge/manage 30 to 40 lithium ion cells, and really liked the feature sets of the BQ76P102 and BQ78PL114. Unfortunately, these are not for new designs, and we would like to know if you have any roadmap devices coming along these lines. Or, do you have any suggestions on how to implement this with your remaining devices.

  • 0
    TI__Genius 10240 points

    From the charger side, we have the solutions charging up to 6 cells of Li-ion battery. 

  • 0 in reply to ezhao
    Prodigy 5 points

    40 LiIon at 4.2V/cell is ~170V series stack.
    1Amp charge at 170V is 170Watts, 2Amp is 340Watts.
    At these power levels a charger would consist of:
    1. AC input, Power Factor Corrected probably, create 190V bus (US 110V line voltage) or 380V bus (International 220V line voltage)
    2. Isolated stage, forward converter, Phase shift full bridge (UCC3895) or active Clamp forward (UCC3897)
    3. Measure voltage and current on isolated output
    4. some control mechanism, analog or digital, to perform Constant Current up to 4.2V/cell, then Constant Voltage taper charge to terminate.

    The TI web has an example:
    http://www.ti.com/solution/battery_management_high_cell_count_for_hev

    The Gas Gauge inside the battery pack would communicate to the charger system.
    It would tell charge current and voltage that the pack is designed for.
    The GG would also report battery status during charge, temperature, and when TAPER current has been reached to stop charging.

    Per the block diagram in the link above, 2 Gauging solutions are given.
    http://www.ti.com/product/bq76pl536a-q1
    This part is STACKABLE and could service 40 series cells.
    Each IC can service 6 cells, so 7 IC's stacked would work for 40 cells.

    http://www.ti.com/product/bq77pl900
    This part is not stackable and not applicable for more than 10 cells.

    I am waiting for the High Cell Count battery management team for other suggestions on the gauging.

  • 0 in reply to Ed Walker
    Intellectual 580 points

    Hi Vic,

    For a 30-40S pack, some options if gauging is a key requirement:

    (a) Gauge based on a subset of the total cell count, for example using the lowest 4 cells and using one of our already released devices (bq3050, bq20z75)

    (b) Gauge based on an "average" voltage of all cells by taking the net stack voltage and dividing this down to the equivalent of a single cell. The recently released bq34z100 would support such an implementation.

    http://www.ti.com/product/bq34z100

    In both cases, the protection side of the BMS would need to be handled with a separate solution; the bq76PL536 that Ed mentioned has a native stacking interface and could be interfaced to a µC, in which you could implement the protection features needed. 

    Thanks,

    Allen