• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 101 subscribers
  • Views 2583 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AM335x : can we control 'drive strength' of usb signals(DP/DM)?

Devin Park
Expert 5965 points

Hi,

I wonder if usb_dp/dm can be also adjusted via register setting. DDR has the feature. Also adding a cap on the DP/DM will be recommended, is it right?

From TRM, I couldn't find the feature so guess that an usb module doesn't have the functionality.

 

Regards,

Devin 

  • 0
    Genius 3685 points

    USB DP/DM have an application-specific drive strength. It make no sense to adjust this strength, because it must be conform to the USB specification.

    If you have problems with EMI, add a 90 Ohm common mode choke to DP/DM. There are special types available for USB 2.0 (480MBit). A cap on DP/DM is not recommended.

    regards

    Wolfgang

  • 0 in reply to Wolfgang Muees1
    TI__Expert 5965 points

    Hi Wolfgang,

    Thanks for your comment and one more question.

    Is there any spec for default drive strength of DP/DM?

     

    Regards,

    Devin

  • 0 in reply to Devin Park
    Genius 3685 points
    Devin,
    you can download the USB specification from www.usb.org.
    The DP/DM differential impedance is specified as 90 Ohm. You have to layout them as differential pair.

    regards
    Wolfgang
  • 0
    TI__Mastermind 27720 points
    The USB module doesn't have adjustable drive strength.

    Also, no caps are permitted on the USB2 signal pair. Please review the USB schematic checklist:
    processors.wiki.ti.com/.../AM335x_Schematic_Checklist
  • 0 in reply to -DK-
    TI__Expert 5965 points

    Hi DK, Wolfgang,

    I have more questions.

    1. If  eye diagram will not meet the spec, how can we adjust it?

        - On TRM, we can see "Termination_control" & "ANA_CONFIG2" registers. Can we use for this purpose?.

                        Termination_control

    HS Code selection control field

    Each increment increases the termination impedance by ~1.5%. Valid values are 000b 011b.

    ANA_CONFIG2

    REF_GEN_TEST field

    0000000b - Produces the typical vertical eye diagram amplitude
    (default).
    1100000b - Increases vertical eye diagram amplitude by 15 mV.
    1010000b - Decreases vertical eye diagram amplitude by 15 mV.
    All other values are reserved.

    RTERM_TEST field

    000b - Typical termination impedance (default).
    011b - Decreases the termination impedance by 2 to 3% and can be
    used to increase the vertical eye diagram amplitude by 1 to 1.5%.
    All other values reserved.

    2. USB spec includes "Receiver Sensitivity TEST". Does AM335x have any register for controlling it?

    B.Regards,

    Devin

     

     

  • 0 in reply to Devin Park
    TI__Mastermind 27720 points
    Devin,
    1) The PHY values are trimmed during final test and shouldn't be changed. You don't mention exactly which portion of the test fails, but please review the layout, component selection, and any schematic issues that may be negatively affecting the DP/DM signal amplitude and/or rise/fall time. The AM335x Schematic Review Checklist is a good place to start.
    2) No. As in #1, the PHY is trimmed to meet the USB spec as part of TI's final test procedure.