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Original question:

TPS65981: Power sink not negotiating for highest available power level when using battery PDOs, prefers fixed supply

TPS65981: Sometimes USB-PD negotiate to a fixed PDO with less power than the battery PDO

Paul51033
Prodigy 220 points
Part Number: TPS65981
Other Parts Discussed in Thread: TPS65987,

Tool/software:

Hello, we still have this issue

When using battery PDOs and configured to negotiate for maximum power the TPS659781 will sometimes instead negotiate to use a fixed PDO with less power available.

Any advice?

Paul

  • 0
    TI__Genius 9710 points

    Hi Paul,

    I took a look at the old thread and I have a suspicion for what is going on. I think the TPS65981 is prioritizing fixed sink contracts over battery sink contracts. The "ask for max" field of each sink PDO works by forcing the TPS65981 to request the maximum power source PDO advertised by the source. I think the TPS65981 is ignoring the battery source PDO when asking for max power. So since the 9V source PDO that TPS65987 advertised has maximum power among fixed source PDOs, that is the PDO requested. I don't have access to TPS65981 anymore, but can you try these settings for the 0x37 Autonegotiate Sink register? These settings should allow the TPS65981 to try and negotiate a maximum power battery sink contract upon connection. You can keep the settings in 0x33 TX Sink Capabilities register the same.

    Best,

    Alex