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BQ79616-Q1: PCB modifications required to use variable number of series cells per chip (12-16)

Part Number: BQ79616-Q1

Hello, I am wondering what modifications, if any, are absolutely required to utilize the same stack chip PCBs with 12 cells (or 12-15) instead of the standard 16 as it was originally configured. We have a need to utilize an already manufactured PCB, which was designed for 16 cells, in an application where there will only be 12 cells per stack chip. I see in the documentation that there are certain resistors and capacitors which are not populated depending on the number of cells connected but I am wondering what the ramifications would be if a board designed for 16 cells was only connected to 12. Is this something that could be handled with only a software change? If a hardware change is completely necessary to ensure the chip functions correctly, could you assist in confirming that depopulating the necessary components would adequately accomplish the goal? Attached is our existing schematic. Let's assume for the discussion that I am looking to use this design with 12 cells instead of 16. I understand that I would need to get the 12th cell connected to the BAT pin as the 16th would normally be. If I were to depopulate R227 and R219 and branch BAT12 to BAT16 would that accomplish the goal? Is this as simple as just shorting all unused VC pins to BAT?

  • Hi Blakely,

    A wire from cell 12 to bat and a wire between negative side of cell 1 to AVSS is all that is absolutely necessary to power the IC and num_cell may be configured for twelve cells. R227 and R219 do not need to be depopulated.

    Shorting C229, C228, and C227 will short all unused VC pins but it will need a short directly to BAT. Removing C230 will reduce the capacitance that would be connected to the BAT pin when the VC pins are shorted to BAT. The reason the VC pins would be shorted to BAT is because there is a back-body diode between BAT and VC16, VC16 and VC15 and so on. The goal is to prevent these diodes from reverse biasing or forward biasing during operation in a noisy environment.

    Regards,

    David