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Question about USB

Yi Yin1
Intellectual 430 points

Hi, 

Is there a internal damping resistor(series resister)  in the D+, D- pin of Am335x's USB ?(Use for  adjusting the  output impedance)

If yes, Is there a register that can adjust the value of the internal resistor ?

 

In the TRM,there is a "Termination_control" (16.5.4 USB2PHY Registers)

But I do not know if the "Termination" is  damping resistor(series resister),

And  I can not find out about the description about "rterm calibration" in any where.

Can you give me some information about this?

Thanks.

Yin

  • 0
    TI__Guru**** 393215 points

    Hi Yin,

    There is no additional public information to what the Datasheet and TRM describe. The USB data lines do not need any external components.

  • 0 in reply to Biser Gatchev-XID
    TI__Guru 63015 points

    The USB PHY inside the AM335x device provides the specified transmission line termination impedance, which you are calling damping resistors.

    All analog parameters related to the USB PHY, including the termination impedance, are trimmed during final test of the device and should be within the values specified by the USB specification.  Therefore, PHY related register values do not need to be adjusted by the user.  This is the reason we do not publish the details of these registers.

    Regards,
    Paul