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[TM4C129x, USB] Exclusive use case for USB internal/external PHY

Naoki Kawada
Guru 19890 points


Hello,

My customer is considering to use USB with both internal and external PHY.
Please note SW controls them exclusively, i.e, if SW uses high speed external PHY via ULPI interface, internal PHY is completely shut down and vice versa.
I think this may be able to realize this, but I don't think it is assumed use case on TivaC. I'm wondering if USB interface should be fixed to use a single dedicated PHY statically, and users should not change the PHY dynamically.
Do you have any comments on this ?

Best Regards,
Kawada

  • 0
    TI__Guru**** 244400 points
    Hello Kawada,

    No, it is not an assumed test case. One of the main discussion points on the external PHY was the speed of operation to go to HS rather than being limited to FS/LS. It is possible to have both interfaces being controlled via SW and then use an external USB multiplexer/demux IC to have a single USB connector. This configuration shall always be software control. However in my known experience I have not seen a customer doing so as the end application in almost all cases is fixed.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 19890 points
    Hello Amit,

    Thanks for your reply.
    Ok, you also think it may be okay, but it is abnormal use case. At least, TI does not assume such use case.
    I think there are some risks to have both phys because of the complication, and the customer has to think about the handling by overall SYSTEM if they go with the current plan.

    Best Regards,
    Naoki
  • 0 in reply to Naoki Kawada
    TI__Guru**** 244400 points
    Hello Naoki,

    That is correct we do not assume such a use case and the customer has to evaluate the requirements first than risk to ensure compliance is met. Having 2 separate physical connectors may still be a valid option.

    Regards
    Amit