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TPS23754: Support PD 25W with dual POE cable

Feng bin Su
Expert 8780 points
Part Number: TPS23754
Other Parts Discussed in Thread: TPS2378

Hi team,

My customer is asking whether they can support 25.5W  of PD with combiner RJ45 ethernet  cable with both of the PSE only can support 15.4W with IEEE802.3af.

Please refer the below link for their ethernet cable.

https://www.amazon.com/WT-MMF-RJ45-Ethernet-Cable-Combiner-Splitter/dp/B01N806BN2

1. Two 802.3af RJ45s are synthesized through wire and provided to 1 PD controller  IC. Can they provide 25.5W PD by dual 15.4W PSE?  They are using our TPS23754 now.

2. How do they do the handshaking since there are two PSE device in system?

Thanks.

  • 0
    TI__Mastermind 21320 points

    Hello Feng bin Su,

    Thank you for your question. So I opened the link to the Ethernet cable, and it says that it supports UPoE. 

    For your background, UPoE is not an IEEE802.3 compliant solution, but it was created to achieve higher power levels before the standard was written. 

    In order to use UPoE, the design will require a PoE PD for each port, and then one DC-DC controller. The TPS23754 has the DC-DC PWM controller integrated into the part, so we cannot use it in this case. We will need to use one of our standalone PD's from our portfolio. 

    The good news is we have an application note and a reference design that implements UPoE. The application note gives some good information on UPoE and how to use it in a design. 

    Application Note: http://www.ti.com/lit/an/slva625a/slva625a.pdf

    Reference Design: http://www.ti.com/tool/TIDA-00741

    Both of these documents use the TPS2378. That would be my recommendation based off the power requirement. 

    If possible, I would highly encourage you to talk to the customer about switching to a higher power PSE. I advocate for this because this simplifies the design, allows the customer to continue to use the TPS23754 and they could enable them to be IEEE802.3 at compliant. The industry is pushing for compliance and getting systems certified since the PoE committee is soon releasing the compliance logo/ tests. More information on this topic can be found on our PoE training page: https://training.ti.com/power-over-ethernet-poe-training-series

    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    TI__Expert 8780 points

    Hi Michael,

    Thank for your help.

    TI's application is 2 port 802.3At combined into U POE: Pout: 51W

    Customer would like to know that can they  use 2 port 802.3Af to combine into POE + Pout: 25.5W?

  • 0 in reply to Feng bin Su
    TI__Mastermind 21320 points

    Hello,

    Yes this is UPoE because the link you sent in your original question was to a device that is UPoE, not POE+. 

    The device listed also says it combines two 802.3at ports into one UPoE port. 

    Here is a link to our PoE+ reference design: 

    http://www.ti.com/tool/PMP6998

    Regards,

    Michael Pahl