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TPS25750: Recommendations for adding secondary charging capability to USB-PD solution

3fti
Intellectual 265 points
Part Number: TPS25750
Other Parts Discussed in Thread: BQ25713, BQ25713B

Our design requires USB Type-C PD functionality as a Sink and Src (up to 100W). The TPS25750+BQ design works well with our current design with one exception; we also require that our battery be able to be simultaneously charged from a secondary power source (non-USB) while acting as a Sink and providing power to the USB-C port. In our current design we use a BQ part to charge the battery, but we can't share the same BQ part with the TPS25750 since they have conflicting power flow direction requirements. We are looking for suggestions for a topology that would resolve this. The secondary power source has variable power capability, and we currently use the BQ to match the charging current to the available power, so we still need to be able to this. 

  • 0
    TI__Expert 8310 points

    Can you please tag the BQ part number? I will forward this to the BQ team who is more familiar with these devices.

  • 0 in reply to Ghouse Mohiuddin23
    Intellectual 265 points

    Tag added, thanks!

  • 0 in reply to 3fti
    TI__Intellectual 1805 points

    Hello,

    Could you provide a block diagram showing the system requirements you need?

    Best Regards,

    Jacob

  • 0 in reply to Jacob Rook
    Intellectual 265 points

    The two modes are shown below.

    In the first, the internal battery is charged from a main power source. The PD controller block must implement the USB-C PD negotiation and generate the correct voltage on VBUS (we are considering the TPS25750+BQ25713 combo to implement this block). A second charger IC (also a BQ part) charges the internal battery from the main power source.

    In the second, the internal battery is charged via the USB-C port and the main power source is still present. I have shown the main power source disconnected from the battery during this mode. However, it would be better if both could charge the battery simultaneously but this is not a requirement.

    Is it sufficient to configure the main power source BQ to deliver 0 charge current to disable it so that only the PD BQ will provide charge? Or do we need add circuitry to perform this disconnect?

    Is it possible to allow both BQ devices to charge the battery in parallel?


  • 0 in reply to 3fti
    TI__Mastermind 34495 points

    Thanks for the block diagram. 

    I think it will work. We have done parallel charger design in the past. Just simply connecting two chargers to the same battery. You can disable one or the other during charging. It allows two BQ devices to charge one battery, since they are current sources. When the battery is nearly full, you can disable one of them.

    To avoid duplicate I2C address,one uses BQ25713, the other uses BQ25713B. 

    I hope this clarifies your question.  

  • 0 in reply to Tiger Zhou
    Intellectual 265 points

    Thank you for the confirmation.

    To clarify one point, it is OK for them both to charge simultaneously but one should be turned off when the battery is close to full so that they don't interfere with each other during the charge termination phase?

  • 0 in reply to 3fti
    TI__Mastermind 34495 points

    In constant voltage mode, the charge current is determined by the battery voltage. It is hard to determine which charger contributes more. The charger is termined by the host anyway. 

  • 0 in reply to Tiger Zhou
    Intellectual 265 points

    Thanks for your insight.