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TPS65986: Constant changing of PD contract with MAC

Eric S
Expert 5640 points

Part Number: TPS65986

We are seeing some unexpected behavior from TPS65986 while our product is attached to a Macbook with a USB-C port.

 

Basically we see the Mac say it can supply 5V / 3A, which TPS65986 successfully requests.  Then, immediately following, the Mac does a 'Get_Sink_Cap', which TPS responses.  Then the Mac advertises it can only supply 5V / 1.5A, which TPS successfully requests.

 

At this point, it starts the whole process all over again.  So we just keep switching between 5V / 3a & 5v / 1.5A non-stop, very quickly.

 

We are assuming that something on the TPS65986 side is causing this behavior, but not sure.  We did notice that the 'mismatch' flag is being set when T2 requests the supply to use.  Perhaps that would cause this behavior?  Any other ideas on what may be configured wrong?

  • 0
    TI__Mastermind 36756 points
    Hi Eric,

    When the 86 board accepts the 1.5A the cap mismatch bit is set since it is really wanting to sink 3A according to the Sink Capabilities. If the 86 is then consuming more than 1.5A, the PD Source (Macbook) will trip OCP. You could check the VBUS current to ensure it is not exceeding 1.5A and also change the minimum current on the Sink PDO to 1.5A to better match.

    Thank you,
    Eric