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Direction of 100Mb Ethernet PoE transformer, choke to cable side or transformer to cable side ?

Ian Middleton
Prodigy 90 points
Other Parts Discussed in Thread: PMP11107

We are implementing a 100Mb 803.3af (13W) PoE PD device, power over two twisted signal pairs and 2 spare pairs. This is feeding from PoE Ethernet cable into a "industry standard" Pulse electronics H2019 PoE transformer, as used in numerous TI reference designs.

Do the signals from the PoE Ethernet cable go to the choke side of the H2019 or the transformer side of the H2019 ?

TI reference designs eg SLUA469 "Practical Guidelines to Designing an EMI Compliant PoE Powered Device...." show PoE cable into choke side of H2019 and PMP11107 "Dual Output Class 3 PoE Converter" show PoE cable side into the transformer side.

My feeling is PoE cable to choke side of the H2019 to limit EMI to/from the cable ?

  • 0
    TI__Genius 15951 points

    Hi Ian,

    Thanks for reaching out to us!

    The CM choke should be on the data only side. You are correct that if the CM choke is placed at the power + data mixed side, the PoE dc current is CM and may saturate the CM choke which reduce the EMI robustness. 

    Updated on Jan/17/2023: It has been a relatively long period that we have not received your reply. I will close this thread for now. Please open a new thread if you have further questions.

    Best regards,

    Diang