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Original question:

TPS25751: BQ25756

BQ25756: The BQ25756 behavior with PD TPS25751

Alex Wang
Prodigy 140 points
Part Number: BQ25756
Other Parts Discussed in Thread: TPS25751

Hi TI,

We want to develop a portable charger with TPS25751 and BQ25656, and we had some questions posted in the previous E2E thread. Chris replied from the PD perspective, but the BQ part still needs to be discussed. 

The BQ related questions are arranged as following, could you please point us in right direction? Thanks.

In this design, we used two pairs of TPS25751 and BQ25656 with two Type-C ports. Suppose there's no MCU control, what would happend if the following situations occur?

(1)Both Type-C ports are connected to connected to the chargers with the same specification respectively. For example, Port-1 connects with 20V, 3A charger, Port-2 connects with 20V, 3A charger. Would the charger current to Battery be the sum of BQ-1's and BQ-2's output IBAT, i.e,  the charger current to Battery is 6A?

(2)Type-C ports are connected to the chargers with the different specifications respectively. For example, Port-1 connects with 20V, 3A charger, Port-2 connects with 5V, 1A charger. In this situation, 5V would be increased to 20V by BQ-2?

(3)Port-1 connects with charger, Port-2 connects with consumer such as mobile phone. Would BQ-1 and BQ-2 work normal in this situation?

Notice the system power is supplied by the battery directly, and the reverse mode would not be used in BQ.

  • 0
    TI__Mastermind 21200 points

    Hello Alex,

    Thanks for being patient with this. I am very busy this week and I will get back to you before Wednesday.

    Best Regards,
    Ethan Galloway

  • +1 in reply to Ethan Galloway
    TI__Mastermind 21200 points

    Hello Alex,

    Thanks for being patient with this.

    1) If 20V/3A available from both ports, that is 60W*2 = 120W available at input. If the battery can accept 120W, then each charger shall deliver 60W to charge the battery. The actual battery current will depend on the VBAT.

    2) In the case where Port-1 is 60W and Port-2 is 5W, BQ-1 shall deliver 60W and BQ-2 shall deliver 5W. The actual output current for each charger will depend on the VBAT. BQ-2 would indeed convert the input voltage to the battery voltage by itself.

    3) BQ-2 would need to be shut off on this case. BQ-1 can charge normally. This should be controlled by the TPS device for the case where we want voltage present at BQ-2 input but no charging. Charger needs to be disabled in this case.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 140 points

    OK, thanks for your reply.