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DP83848Q-Q1: Recommended register setting

Tomoaki Yoshida
Expert 2200 points
Part Number: DP83848Q-Q1


Hi,

My customer is consifering DS83848-Q1 for Ethernet phy.

They will do noise evaluation etc.

Please tell us about the recommended register setting for noise evaluation.

Is there a recommended setting for the following bits of PCSR (Datasheet: Table 5-21)?

  ・TQ_EN

  ・SD FORCE PMA

  ・SD OPTION

  ・FORCE _100_OK

  ・NRZI_BYPASS

Best regards

Tomoaki Yoshida

  • 0
    TI__Mastermind 19780 points
    Hi Tomoaki-san,

    It is recommended that the default configuration be used for noise evaluation with the DP83848Q.

    If there are any issues seen during noise testing, it may be possible to debug using the advanced features you have mentioned.

    Best Regards,
  • 0 in reply to Rob Rodrigues
    Expert 2200 points

    Hi Rob-san,

    Thank you for your reply.

    Althought you recommended that the default configuration be used for noise evaluation, is there a function or register setting that affects noise?

    Even if they evaluate by default, they may know what registers should be set to improve noise.

    Please tell me the reason for recommending the default.

    Is it best perfomance condition for noise?

    Best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida
    Expert 2200 points
    Hi Rob-san,

    I have additional questions.
    please answer me.

    #1
    Is there a feedback resistor between X1 and X2?
    If there is not a feedback resistor, we think that an external feedback resistor is necessary.

    #2
    Is there any spice model that can be offered?
    I know to be released IBIS model in web site.
    I need a spice model because I want to verify it in combination with a power supply.

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida
    TI__Mastermind 23675 points
    Hi Tomoaki-san,

    The default register values are the best configuration for noise.
    An external feedback resistor is not required.
    We do not have a spice model for the DP83848. We only have an IBIS model.

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Expert 2200 points

    Hi Ross-san,

    Thank you for your reply.

    I would like to confirm about feedback register.

    I understood that it is not needed an external feedback resistor.

    Our customer met where oscillation stops due to condensation or external impedance change when using a PHY without internal feedback resister the past.

    So, if there is no internal feedback resistor, they think that it is necessary to attach an external feedback resistor.

    They perform oscillation test by inserting a variable resistor at X1 terminal and GND or Vdd.

    Could you tell me wheter is there internal feedback resistor?

    And if there is internal resister, could you tell me its value, too?

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida
    Expert 2200 points

    Hi Ross-san,

    Thank you for your support.

    Any update on this issue?

    I would like to know whether is there internal feedback resister.

    Best regards,

    Tomoaki yoshida