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DP83822IF: TD+/TD- signals: Steep slew rate causes overshoot

Dierk Bronner
Intellectual 1905 points
Part Number: DP83822IF

Hi team,

my customer is planning to use the DP83822IF in one of their systems but facing some EMI challenges.

 

The transmission signals of the device TD+ and TD- do have a very steep slew rate and showing overshooting. This causes some interference on their design -  it gets coupled into the secondary side of the transformer 

Question:

Is there a way to slow down the slew rate somehow? For them it doesn’t matter through SW control or due changes on the circuitry.

Or any other way to improve the overshooting what causes the interference? 

 

Can you please help us out here – Thank you very much!

 

Kind regards

Dierk Bronner 

  • 0
    TI__Mastermind 18425 points
    Hi Dierk,

    To start, can you check the following on the customer design?

    1. Check that the magnetics meets the characteristics mentioned on page 104
    2. Check that RBIAS is 4.87kohm with 1%tolerance.
    3. The termination connections match the TPI Network Circuit diagram on page 92. The 49.9ohm resistors should be 1% tolerance and should be kept as close to PHY as possible.
    4. TD and RD traces should be 100ohm differential.

    -Regards
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Intellectual 1905 points
    Aniruddha,

    thanks a lot for your response. We were able to get additional support and reviewing the layout in the next steps.

    Kind regards
    Dierk Bronner