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bq76PL536A High cell count string

Douglas Malouf
Intellectual 405 points
Other Parts Discussed in Thread: BQ76PL536A

Hello there,

We intend to use bq76PL536A in a 30S1P 20Ah LiFePO4 pack for balancing. The total string has 6 packs, which means we have 180 cells in serie. Due this configuration, I have the following doubts:

1. As each pack has its own PCM with 5 vertical ICs, for each IC is necessary a different ground reference. So, for a vertical SPI connection between two packs, is necessary to bring the ground reference of the upper pack (southest IC) to the lower pack (northest IC) ?

2. Due the high voltage of the uppers pack of the string, the BAT1 and 2 pins of these packs must reduced to 36V or can be connectes directly to most positive cell? 

3. During balancing, care shall be taken to avoid selecting the upper cell of the lower pack to be balanced together to the lower cell of the upper pack or both packs can have its own balancing algorithm and work independently?

Thank you in advance.

Douglas

  • 0
    TI__Intellectual 2795 points

    Hi Douglas,

    To answer your questions:

    1. No. Each IC is referenced to the bottom of the lowest cell it is connected to.

    2. BAT1 and BAT2 of each IC will be attached to the top of highest cell (5) it is connected to.

    3. There should not be any concern. The measurement may be slightly offset, but you should expect this if measuring while balancing is enabled. Since the balance current is known, and the decision of which cells are selected for balancing is known, the algorithm can take this into account to apply the necessary offset to the cell measurement. Please remember that the bq76PL536A does not contain a balancing algorithm. This is provided by the host controller.

    Regards,

    Stephen