2
\$\begingroup\$

I have a non-standard Power over Ethernet application (connector, and devices are not ethernet standard but we are using ethernet pairs and protocol for communications). On looking at PoE schematics I have noticed that none of them incorporate common mode termination in the design. Isn't common mode termination needed at all, or does the PoE standard reduces maximum cable runs to compensate?

I was planning to use the following circuit for termination (with its equivalent on the ground side, values are estimates), is this overkill?

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
1
\$\begingroup\$

I'm not sure which schematics you have looked at, but many I have looked at do include termination. POE doesn't really change things in that regard.

See this question:

Bob Smith Termination with POE

Also:

http://www.ti.com/lit/an/slua454/slua454.pdf

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ I guess I had been looking at "simplified" and conceptual schematics in the data sheets. They just show diodes connecting directly to the magnetics. Even in some actual schematics of PoE injectors they just allow the common mode to pass through!! (rather silly if you ask me). So they have no termination whatsoever. \$\endgroup\$ – Edgar Brown Oct 31 '18 at 18:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.