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TPS65987DDK: Should USB2 DP/DN Signals Be Left Disconnected?

Cletus
Prodigy 120 points
Part Number: TPS65987DDK

I understand that the TPS65987DDK doesn't support BC1.2 (the firmware release notes (F907.14.05) state that BC1.2 isn't supported).  Because of this, should the USB C USB2 DP/DN lines route directly to their endpoint IC (in my case the LAN7801) instead of also going to the C_USB_P/N pins of the TPS65987DDK ?  Doing this will obviously make BC1.2 support impossible, but that is fine in my application.

  • 0
    TI__Expert 6280 points

    Hi,

    Yes, the USB2 lines can be connected directly to your endpoint and you can leave the USB D/P pins on the PD controller disconnected.

    Jacob

  • 0 in reply to Jacob Ontiveros
    Prodigy 120 points

    Jacob,

    Thanks for the quick response, that answered my original question.

    Another question:  does the TPS65987DDK interreact with the C_USB_P/N pins at all (provided they're not configured as GPIO)?  I ask to rule out any potential interference with the USB Device controller on our board. 

    Our TPS65987DDK is configured as a DRP and our board serves as the USB PD Power Source and a USB C UFP (Device).  The attached partner is a Samsung S20 which will become the USB PD Power Sink and USB DFP (Host).  Our current design has the C_USB_P/N connected to the TPS65987DDK via short stubs on the path going to the USB Device controller (LAN7801).  After a plug event, we keep the LAN7801 in reset until the TPS65987DDK has completed the power negotiations (the attached phone indicates it is charging at a USB PD rate), then enable the LAN7801. 

    Once we enable the LAN7801, the attached phone will reboot 50% of the time.  On the times it doesn't reboot, it successfully enumerates the LAN7801 and shows it as an ethernet adapter.  If it automatically reboots, it also successfully enumerates the LAN7801 and shows it as an ethernet adapter.  Besides the reboots, everything is working correctly, but we'd like to eliminate the reboots.

    On the surface, it would appear that the LAN7801 is misbehaving and causing the phone to reboot because the reboots only come after it is enabled.  This may indeed be the case, but the 50% probability of reset makes me wonder if it is a side effect (Samsung driver bug?) of the USB PD negotiations because when two DRPs are connected, they'll need to undergo a UFP/DFP role swap 50% of the time. 

    We're still actively debugging this, but any thoughts or tips would be appreciated.

    Thanks,

    Cletus

  • 0 in reply to Cletus
    TI__Expert 6280 points

    Hi Cletus,

    If you disable the GPIO they would be Hi-Z. It might be a driver issue, another way you can double check this is with Windows system and check the enumerations logs. This is out of the scope of the PD controller so you will have to check resources online. 

    Jacob

  • 0 in reply to Jacob Ontiveros
    Prodigy 120 points

    Jacob,

    Ok, thanks.  We're going to use a USB PD + USB 2.0 analyzer (Lecroy Mercury T2C) to sniff the traffic and see exactly what's going on.

    -Cletus