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TPS25751: Can the PD limit the current from PPHV?

Bill Norton
Prodigy 230 points
Part Number: TPS25751

Tool/software:

If the PD establishes a PPS contract specifying 500mA operating current, can it limit the current from PPHV to 500mA?

If so, what settings in the USBCPD Application Customization Tool would accomplish that?

Transmit Sink Capabilities Extended Data Block (0x7e) looks promising, but the TRM doesn't describe it.

  • 0
    TI__Mastermind 30322 points

    Hi Bill, 

    Thank you for reaching out!

    Is the TPS25751 being paired with a battery charger? 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 230 points

    No battery charger, sink-only.

    With a PPS contract for 12V 500mA, I found I can draw about 1 Amp from PPHV before something shuts off.

    Same thing for a 12V 250mA contract.

    Is it trying to current-limit per the contract, or is it triggering thermal protection or something?

    A fixed 12V 500mA contract drew over 2A before my load overheated, so for low currents PPS is the way to go.

  • 0 in reply to Bill Norton
    TI__Mastermind 30322 points

    Hi Bill, 

    The TPS25751 alone does not limit the current on PPHV. Typically, when paired with a battery charger, the TPS25751 will set the current limit on BQ according to the PD contract. 

    In your case, are you observing PPHV open? 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 230 points

    No, I'm not seeing PPHV open, at least not that I can tell by measuring the voltage on it.

    I measured PPHV current and voltage after establishing a PPS 12V 250mA contract.

    Is it limiting the current by reducing the voltage?

    0A          11.94V

    .016A    11.94V

    .030A    11.93V

    .136A    11.89V

    .218A    11.86V

    .278A    11.83V

    .392A    11.80V

    .665A    11.71V

    .790A    11.67V

    1.064A  5.445V

    1.077A  2.224V

    0A          0V

  • 0 in reply to Bill Norton
    TI__Mastermind 30322 points

    Hi Bill, 

    Thank you for providing the measurements on PPHV. 

    It appears to be that the power adapter (Source) is limiting the current on its end or going into a brown-out condition where is it unable to maintain the 12V contract. 

    Best Regards, 

    Aya Khedr