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TUSB321AI: DIR Pin not working

Marcel Thürmer
Prodigy 20 points
Part Number: TUSB321AI

Tool/software:

Hi there,

I'm currently working on a design with the TUSB321AI, USB 3.0 Mux and an USB C Host Port.

However the TUSB321AI never changes the value of the DIR Pin to switch the Mux around. I confirmed that both CC Pins have a proper voltage as expected.

If I swap the plug polarity around, the voltages on the CC Pins also swap around accordingly.

Could somebody review my schematic if I made a mistake?

Best Regards,

MarcelUSB_C_Mux_H1.pdf

  • 0
    TI__Mastermind 38955 points

    Hi Marcel,

    Are you using the ID pin to control VBUS? I don't see anywhere the ID pin may be routed to on this schematic. If not, then the CC negotiation process may not be successful, causing the DIR pin to not change and the port to only work in one orientation.

    The ID pin should be used to control VBUS when the ID pin is low via a power switch or GPIO of the SOC. Please confirm this is being utilized properly.

    Thanks,

    Ryan

  • 0 in reply to Ryan Kitto
    Prodigy 20 points

    No, we based our Design on the example from our SoM Manufacturer:

    In this example the ID Pin isn't used aswell. 

    However if I remove the VBUS_DET resistor the TUSB321AI switches the DIR Pin accordingly.

  • 0 in reply to Marcel Thürmer
    TI__Mastermind 38955 points

    Hi Marcel,

    If the ID pin, then how is VBUS being supplied? Is it being controlled elsewhere, or supplied at all times?

    VBUS_DET should not be needed for a DFP application, so removing that is okay.

    Does the DIR pin work for both cable flip orientations? We typically expect it to only work on one side if VBUS is not being controlled.

    Thanks,

    Ryan

  • 0 in reply to Ryan Kitto
    Prodigy 20 points

    VBUS is being supplied through an USB Power Switch which is controlled by the USB Host.

    Yes both directions work.

  • 0 in reply to Marcel Thürmer
    TI__Mastermind 38955 points

    Hi Marcel,

    If both directions work, then it seems like the TUSB321AI is working as expected.

    I would still recommend using the ID pin to control VBUS, just to ensure that this does not potentially become an issue down the line.

    Thanks,

    Ryan

  • 0 in reply to Ryan Kitto
    Prodigy 20 points

    Thanks for your help, If I want to use the USB C Port as Board to Board Interconnect without a cable, I need to manually swap the TX and RX Lines around since the swap is usually done in the USB C Cable?

    I want to mount an USB C camera directly to my board without any cables in between.

  • 0 in reply to Marcel Thürmer
    TI__Mastermind 38955 points

    Hi Marcel,

    Correct, the TX of the host needs to go to the RX of the device, and the TX of the device needs to go to the RX of the host. If a type-C cable is not being used, then you'll need to manually route these lanes accordingly.

    How is the connection for this going to be? Camera board -> Motherboard/SOC board -> Type-C port?

    Thanks,

    Ryan