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TPS25730: How to operate with separate PD Protection

Joe Paolino
Intellectual 470 points
Part Number: TPS25730

Hello,

I have designed my board with separate Short to VBUS protection device on the CC lines capable of protecting against 28V.  The protection device includes dead battery pull down resistors.

Layout Flow:

USB C Connector -> Protection Device ->TPS25730 (The protection device only isolates the TPS25730 from the CC lines)

Power Sequence:

  1. Cable Connected
  2. VBus provided to TPS25730
  3. After several mS delay, 3.3V is supplied to TPS25730(VIN_3V3) and protection device
  4. 2.5-5mS after the protection device receives 3.3V it passes CC lines to TPS25730 and disables its dead battery pull down resistors

Almost immediately after this, VBUS cycles on and off continuously.

For reference a USB A to USB C retains its VBUS connection to my board leading me to think the issue is with the CC lines.  The board powers up without issue.

R99 has been removed so that min operating is 0.5A.  With a pull up on Fault_In, no power seems to pass through the TPS25730.  With a pull down on Fault In, the behavior matches what I describe above.

What have I done incorrectly that is causing the source device to cycle VBUS?

Thank you,

Joe

  • 0
    TI__Genius 12665 points

    Hi Joe,

    I'm not sure of the exact reason VBUS is cycling after the CC lines are connected, but I do suspect it has to do with how the protection device interrupts the Type-C connection process. When VBUS is initially provided to the port and the TPS25730 (with protect device off), the TPS25730 has no CC connection with the far-end source. I think the protection device's late removal of the dead battery pull-down resistors is causing a break in connection with the far-end source, after which the TPS25730 attempts to form its own connection with the far-end device in a weird state.

    Can you capture with an analyzer/scope, CC1/2 at connector, CC1/2 at PD, VBUS, PPHV, LDO_3V3, VIN_3V3. The timing of these some of these signals will help us debug what is happening. Do you also have the ability to capture PD logs with a PD analyzer of some sort? 

    Best,

    Alex

  • 0 in reply to Alex Liu
    Intellectual 470 points

    Thanks for the response. I'll work on capturing these signals.  I do have a logic analyzer that has the ability to decode BMC.

  • 0 in reply to Joe Paolino
    TI__Genius 12665 points

    Thanks Joe.

    Looking forward to reviewing the logs once you’ve collected them. The logs will let us see what is going on more clearly and help root cause the issue as well.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Intellectual 470 points

    Alex, I used the TPS25730's LDO_3V3 to power the protection device (NX20P0407).  Now the board powers up and does not cycle.  I noticed the TPS25730 takes 10mS before it reads the configuration and attempts power negotiation.  With the new power configuration, the TPS25730 powers the protection device while having its own dead battery Rd resistors still active.  The source does not appear to be aware of the switchover.