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DP83869HM: RJ45 termination using 100 ohm for noise suppression, channel A and B

Aneesh Kumar Gopalakrishnan
Prodigy 60 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Tool/software:

Hi team,

I’m working on a 100M media converter (100BASE-TX to 100BASE-FX) using the DP83869 PHY chip. I have a doubt about termination for suppressing unwanted noise. On the magnetics connection side, I’m using the 10/100BASE-T single port surface mount magnetics instead of 1000BASE-T. Hence, channels A and B will be unused. However, we connect one 100-ohm resistor for termination. Is this fine? Can you share your comments, please?

Thank You

G. Aneesh Kumar

  • 0
    TI__Mastermind 19621 points

    Hi G. Aneesh Kumar,

    Thank you for submitting your query. Firstly, is there any reason why you chose to use Channels C & D for 100Base-TX instead of Channels A & B? Note that Mirror Mode will need to be enabled for Channel C & D to function.

    Secondly, the 100Ω termination is okay, but unnecessary. If the extra two pairs are going to be unused, they can be left floating.

    Regards,

    Alvaro

  • +1
    Prodigy 60 points

    Hi Alvaro,

    Thank you for answering my question. Yes, we enabled mirror mode for routing feasibility. Based on your comments, I believe there is no need to add any termination resistors.

    Thank you,

    G. Aneesh Kumar