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LM5156H: Isolated power supply design for PoE PSE Application

Matt Calvo
Genius 14275 points
Part Number: LM5156H
Other Parts Discussed in Thread: TPS23861, , LM5156

Hey Boost Regulator team,

I have a customer evaluating the LM5156H for a new project where they need to implement an isolated 24V to 48V boost circuit in order to power the PoE PSE system which uses the TPS23861. The PoE power requirement is 30W per port so we need a boost circuit that can support ~100W total. The LM5156HEVM-FLY dev kit and design seems to support 5V out at 4A and we're hoping the circuit can be modified to fit the requirements for this application.

A couple questions on our side:

  1. Can the LM5156HEVM-FLY Schematic depicted in Figure 6-1 of the EVM design guide be used to achieve the isolation requirements for the PSE controller that was described above?
  2. Is the isolation transformer from the LM5156HEVM-FLY BOM capable of handling 100W?
  3. Are there any other constraints or limitations we should be aware of going into this power tree design?

Let us know if anything needs further clarification! 

Best regards,

Matt Calvo

  • 0
    TI__Mastermind 23340 points

    Hi Matt,

    Thanks for using the e2e forum.
    It is possible to use LM5156 for 100W flyback applications, however there would be some adjustments on the EVM to make this possible:
    - check input/output caps and replace with higher voltage rating parts if necessary
    - adjust sense resistance, feedback divider and compensation
    - check if FET can support the voltage ratings
    - The datasheet of the transformer should list the saturation currents. If they would be exceeded in the new application, the part has to be replaced

    I found one reference design which is rated for 48W output power.
    This is still lower than the requirements here, but it might still be useful.
    https://www.ti.com/tool/PMP30722

    Best regards,
    Niklas

  • 0
    Prodigy 90 points

    Hi Niklas, 

    Thanks for your reply. Yes, I can definitely use the LM5156, would it be possible to provide a high level schematic or can i use Webench for alternates on FET and isolation xfmr? The caps I can find replacements just fine but for the xfmr its been very hard to find one that is rated for 100W on PSE application. Any recommendations are highly appreciated. 

    Thanks,

    Snigdha

  • 0 in reply to Snigdha B
    Prodigy 90 points

    Also, any training materials on isolation xfmr specific to PSE application for POE would be super useful. 

    Thanks,

    Snigdha

  • 0 in reply to Snigdha B
    TI__Guru 61375 points

    Hello Snigdha B,

    Please check with your transformer supplier on such a training material.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 90 points

    I currently am unable to find a transformer for this application and I'm looking for help from your end to find a suitable part for use with LM5156 / LM51561x for 100W POE PSE system.

  • 0 in reply to Snigdha B
    TI__Mastermind 49751 points

    Hi Snigdha,

    you can try the reference designs database:

    TI Reference Designs Library

    Maybe you can find a design and a transformer which does fulfill your requirements.

    You also can see some vendors which had been used here. Often Flyback transformers are customer designs and a transformer vendor can support you here.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 90 points

    I'm looking to use the LM5156 part as i have mentioned earlier and I was able to find a reference schematic that fits my needs. Can you please confirm the included isolation transformer will work for 100W (20 W per port) application please?

  • 0 in reply to Snigdha B
    TI__Mastermind 49751 points

    Hi Snigdha,

    can you share the reference design ID or transformer part number.

    This would make it much easier.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 90 points

    TIDRRO1 is the one I could find that closely matches my requirements. However current is limited to 0.6A while I'm looking for ~ 2.5A at 48V output and also an isolation transformer to go with it to support 100W application.

  • 0 in reply to Snigdha B
    TI__Mastermind 49751 points

    Hi Snigdha,

    no, this transformer will not be able to deliver the required power but you can e.g. contact and work with Wuerth or any other inductor vendor to tailor an flyback transformer for your needs.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 90 points

    I was hoping you could provide an alternate part that could be used for PSE POE for 3 ports design. Do you have any Isolation transformers used for POE applications that can deliver 100W?

  • 0 in reply to Snigdha B
    TI__Mastermind 49751 points

    Hi Snigdha,

    have you already checked the available reference designs, if there is one available which is close to your requirements.

    There are some with 100W and more.

    TI Reference Designs Library

    Note: Flyback with 100W and more is already on the limit for this topology. You may have to use active Clamp instead.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 90 points

    I found this to be the closest match to my requirements: https://www.ti.com/tool/PMP31092

    Do you recommend this for the PSE POE application? Any limitations that I should be aware of?

  • 0 in reply to Snigdha B
    TI__Mastermind 49751 points

    HI Snigdha,

    thank you for checking our reference designs.

    Yes, this design matches very closely the parameters you have given above.

    As I am not an expert on the PSE POE I really can not judge if this will provide all the required parameters for this application,

    e.g. step response, output voltage ripple

    I will forward this request to the power design team - perhaps they can help further.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Genius 14275 points

    Thanks for all your help with this Stefan and for reassigning this post to keep the discussion progressing!

    Hey TI Power Design Team,

    Can you please help to comment on the latest questions from my customer, Snigdha, who has been very patient trying to determine the best pathway forward for a power solution for their PSE PoE application.

    For reference, I also have an internal ticket with your team ongoing (PDS-5298) so I just wanted to let you know that this is all related to the same opportunity.

    Feel free to comment back on this thread with any follow-up questions you may have for Snigdha!

    -Matt Calvo

  • 0 in reply to Matt Calvo
    Prodigy 90 points

    Thnk you Matt and Stefan. Can you please help on the transformer alternates please, BOM lists PN to be ZB1292-BL from coilcraft which I couldn't find anywhere. If you can please provide list of approved alternates, that would be awesome!