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Original question:

TPS26750: USB Power Delivery (PD) 3.1 Power Derating

TPS26750: USB Power Delivery (PD) 3.1 Power Role Swap

Simon Oettle
Prodigy 60 points
Part Number: TPS26750

Tool/software:

Hello,

we are currently working on device using a host-controlled DRP TPS26750 to charge/discharge a battery through a battery management system (BMS).

The host MCU communicates with the BMS, which provides information in case the battery is not allowed/supposed being charged/discharged (or both).

Initially the TPS26750 is configured as a DRP, but if the connected battery is currently not capable of being discharged, the USB port should not act as a source (and the other way around).

Which registers need to be manipulated to make the TPS26750 switch from acting like a source (DRP USB state machine) to a sink?

Is it necessary to update the USB state machine to "SOURCE only" / "SINK only" or is it allowed to operate as a DRP offering e.g. 0 source capabilities?

Could you please provide me the name of all the registers which need to be manipulated?

  • +1
    TI__Mastermind 37855 points

    Hi Simon,

    Here are the registers and fields that govern the power role:

    • Port Config (0x28)
      • TypeC State Machine
    • Port Control (0x29)
      • Process Swap to Sink
      • Initiate Swap to Sink
      • Process Swap to Source
      • Initiate Swap to Source

    If you want to disable sourcing:

    • Type-C State Machine
      • Sink only
    • Process Swap to Source
      • Disabled
    • Initiate Swap to Source
      • Disabled

    If you want to disable sinking:

    • Type-C State Machine
      • Source Only only
    • Process Swap to Sink
      • Disabled
    • Initiate Swap to Sink
      • Disabled

    You do not need to modify the TX source or sink caps registers. By setting the port config and control fields, the PD controller should never enter the source or sink role.

    Also, pay attention to the register descriptions in the TRM.

    Changes to the Port Control register have no effect on the current contract, and requires a separate disconnect or renegotiation of the PD contract for the new settings to take effect.

    Changes to the Port Config register cause a port disconnect and reconnect with the new settings.

    In your case, it would make sense to modify the Port Control register first, then the Port Config register, in order to trigger the reconnect after all changes have been made.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Prodigy 60 points

    Hi Chris,

    thank you for your quick answer, these settings seem reasonable!

    Is it possible to send you a private message to resolve an USB PD communication issue?

    Thanks and regards,

    Simon

  • 0 in reply to Simon Oettle
    TI__Mastermind 37855 points

    Hi Simon,

    Could you give me a summary of the issue on the public forum, is there any specific reason why you prefer to move to private messages here? Outside of schematic and layout, most features and behaviors of the PD controller shouldn't be restricted to private forums.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Prodigy 60 points

    Hi Chris,

    in the meantime I was able to solve the issue and thus no longer need any further help regarding this topic, but thank you for offering your help!

    Kindest regards,

    Simon