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DP83869HM: Ethernet transformer turns ratio tolerance

Ben van den Bergh
Intellectual 526 points

Part Number: DP83869HM

Dear forum members could you please comment on the following?

From the data sheet of the DP83869HM (SNLS614D – SEPTEMBER 2018 – REVISED JUNE 2025)
Page 112, Table 8-3.

It states that the Turns ratio should be 1:1 with a tolerance of +/-2%
Could you please elaborate on this requirement?

Thank you

Regards

 

  • 0
    TI__Mastermind 36535 points

    Hi Ben,

    Turns ratio tolerance is the acceptable deviation from the 1:1 spec that manufacturers cite for their turns ratio. This should be shown in the magnetics datasheet, such as this excerpt from Pulse electronics' HX5008FNL:

    For example if a transformer has 100 turns on one side, a 2% tolerance would allow between 98 to 102 turns on the other side.

    Best,

    Shane

  • 0
    Intellectual 526 points

    Hi Shane,

    Thank you very much for your reply.
    I realize its a tricky question but how important is this parameter?
    The lower the tolerance the more margin one would have on the voltage swing given the same PHY.
    But how sensitive is this particular device to such tolerance variation.

    Often transformer manufacturers don't state this tolerance.
    We have a case now were we have to request this data from them. 

    Thank you

    Regards
    Ben

  • +1 in reply to Ben van den Bergh
    TI__Mastermind 36535 points

    Hi Ben,

    This tolerance is very important for the reason you mentioned. If the turns ratio strays too far from 1:1, the voltage swing on one side of the magnetics will be different from the other side. 2% tolerance is recommended, however 3% should be ok as well for functional communication. This is noted in the DP83869 troubleshooting guide:

    I do not recommend using magnetics with more than 3% tolerance.

    Best,

    Shane

  • 0 in reply to Shane Hauser
    Intellectual 526 points

    Hi Shane,

    Thank you for the accurate and prompt response.
    Regards