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TPS25751: Configuration for Exclusive 18V PPS Sink

Bryan Lober
Prodigy 10 points
Part Number: TPS25751

Tool/software:

Subject: Inquiry: TPS25751S Configuration for Exclusive 18V PPS Sink

I am configuring a TPS25751S for a new application and am aiming for a specific power sink behavior.

Desired Outcome: My objective is to configure the TPS25751S to always negotiate and request 18V at up to 3A via PPS, and to only advertise this specific power capability to connected USB-C Power Delivery sources.

Observed Tool Behavior & Current Workaround: Using the USBCPD Application Customization Tool (Advanced Configuration), I encountered a challenge in achieving this exclusive 18V PPS negotiation:

  1. When attempting to set "Number Valid PDOs" to 1 and configure Sink PDO 1, the "Supply Type" for Sink PDO 1 appears locked as "Fixed" (likely defaulting to 5V/3A), preventing it from being changed to a "Sink PPS" type.
  2. If I set "Number Valid PDOs" to 2, I am able to configure Sink PDO 2 as a "Sink PPS" with the desired 18V (Min 18V, Max 18V) and 3A (Max Current 3A). However, reducing "Number Valid PDOs" back to 1 then removes this configured PPS PDO, leaving only the original 5V fixed PDO.

To work around this, my current configuration involves:

  • Setting "Number Valid PDOs" to 2.
  • Configuring Sink PDO 2 as "Sink PPS" for 18V @ 3A.
  • Enabling "PPS Enable Sink Mode" in "Autonegotiate Sink / Sink PPS Controls".
  • Setting "Auto Neg RDO Priority [0]" to 1 in "Autonegotiate Sink / Autonegotiate Control" to prioritize Sink PDO 2.
  • "Support PPS Status" was also checked in "PD3 Configuration (0x42)" (though its direct relevance to the core negotiation preference is unclear).

Question for Support: While this workaround appears to prioritize the 18V PPS negotiation, it still results in the device advertising two Sink PDOs (the 5V fixed and the 18V PPS).

Is there a more straightforward or cleaner method within the USBCPD Application Customization Tool or for the TPS25751S itself that allows it to exclusively advertise and always request 18V @ 3A PPS, without having to include a fixed 5V PDO in its Sink Capabilities advertisement? My goal is to streamline the negotiation to only offer and seek the 18V PPS.

Thank you for your time and assistance.

  • 0
    TI__Mastermind 34256 points

    Hi Bryan, 

    Sink PDO1 is always locked to 5V/3A because that is what the USB-IF PD specification requires. However you can configure TPS25751 to only allow 18V/3A PPS contract to enable TPS25751S PP_EXT by enabling this bit below in register Autonegotiate Sink (0x37): 

    When this bit is enabled, TPS25751S will not enable PP_EXT unless the negotiated contract is a PPS type. For example, if the attached source can only offer 5V/3A fixed, TPS25751S will still negotiate this contract but will not enable its sink power path (PP_EXT) to allow the 5V/3A into the rest of the system.

    Let us know if you have any further questions or concerns! 

    Thanks and Regards,

    Raymond Lin