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BQ25756: Dual Battery Charger with TPS25751

Derek Wilson
Prodigy 40 points
Part Number: BQ25756
Other Parts Discussed in Thread: TPS25751,

Tool/software:

I would like to charge two 9S batteries (~39 V) in parallel using a single USB-C PD adapter. These batteries may be at very different charge states when connected, so they each need their own BQ25756.

Looking at the BQ25756 reference design, the TPS25751 can be used to handle USB PD negotiation and configuration of the BQ25756 over I2C. However, I believe two TSP25751 devices cannot be used on the same bus, since they would both try to negotiate with the adapter simultaneously. I thought of using a single TPS25751 for negotiation, but then I'm unsure how to automatically configure both BQ25756 devices through the one chip, since there is only one I2C bus.

Does TI have any advice for how to tackle such a design? Thanks in advance.

  • 0
    TI__Mastermind 30705 points

    Hello Derek,

    Thanks for working with this. I think you'll need an MCU for the power contracts. Each BQ25756 will need to have the input current limit set to half of the usual limit. This will prevent both BQ25756s from crashing the USB adapter.

    To communicate with both BQ25756s, I recommend using an I2C mux. If your battery voltage was slightly lower, I would recommend using a BQ25756E which has a different I2C address from the BQ25756, but the BQ25756E has a max charge voltage of 36V.

    Let me know if you have any questions about this.

    Best Regards,
    Ethan Galloway