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I've been looking through a few application notes for Power over Ethernet front ends such as Microchip AN3468 and Skyworks AN1130.

I can't figure out what the characteristic impedance of the differential pairsets should be. In particular, I'm interested in the input section from the RJ45 to the discrete magnetics that separate the power from the data for PoE.

If anyone could shed some light I'd love to find out more.

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    \$\begingroup\$ IEEE Ethernet standards are free downloads with registration. You really should refer to those documents and have them handy when doing anything Ethernet-related :) \$\endgroup\$
    – Kuba hasn't forgotten Monica
    Commented Apr 20, 2022 at 9:37
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    \$\begingroup\$ I did try to access those before posting but couldn't access even though I was signed in. I tried again after reading your comment and submitted some extra information. Now I have access to those documents. Thanks \$\endgroup\$
    – lgflorentino
    Commented Apr 20, 2022 at 13:03

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Ethernet differential impedance is 100 ohms.

Adding PoE into the mix does not change that in any way, and since PoE is an add-on feature to Ethernet, this is the reason why the documents you linked to talk only about how to implement PoE, not how to implement Ethernet.

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  • \$\begingroup\$ OK, that makes sense. Thanks for clarifying. \$\endgroup\$
    – lgflorentino
    Commented Apr 20, 2022 at 6:11

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