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PMP4909: Simpler schematic design for a smaller board

Part Number: PMP4909
Other Parts Discussed in Thread: TPS23731

Hi Guys,

Please help to suggest a possible solution for a smaller board/simpler circuit for PMP4909 reference design. I have reposted the customer's full inquiry below to explain it further. 

"I am using an evaluation board you have called "PMP4909" and I want to know if a part of the schematic can be removed as I don't need it in my application. See attached image.

In the image above, I would like to keep the red box as that will be the power input for my application. I would like to remove the blue and orange area as I believe they are for connecting voltage directly, I will not have this need for my application and therefore I would like to remove it from the schematic if possible

If the POE input is supposed to be DC or AC? I do assume its DC but its my first time working with POE and I'm not sure how to connect the POE port to this schematic.

Since this is an evaluation board, is there any way I can make this board smaller but still keep parts on the top side of the PCB?

I know this is an old IC but if you can suggest any other newer IC's that can provide the same output of 12v 30W Class 4 POE+ which have a simpler schematic then please do suggest them as I am trying to make this design as small as possible and having a more integrated IC would help greatly."

Thank you so much.

Best regards,


  • Hi Jonathon,


    Thank you for your question.


    Since the customer is new to PoE, I recommend they take a look at our POE training portal and videos here: We have 4 short videos that are a few minutes each that go over PoE intro to the standards, handshake, operation, etc. I think this may be helpful.


    The LC filter in the orange box in the schematic is suggested for EMI purposes so we do not recommend that it is removed. You will find similar circuitry in all of our reference designs for that reason. J1 can be removed in the blue box but the 0.1uF cap is recommended to stay for EMI.


    The red box in the schematic is where power will come from the PSE after it passes through the diode bridge on the PD front end. This power will flow through that LC EMI filter which is why we recommend keeping it.


    For a smaller and simpler 12V/Class4 reference design, I recommend they take a look at:


    1. PMP22806
      1. This reference design uses the TPS23731 in a primary side regulated flyback topology. The benefits of PSR are smaller solution size when compared to a topology requiring secondary side regulation since the opto-feedback network can be removed. This will help with lower system level cost and smallest/simplest size.
      2. This reference design is not on yet but I will send you the reports privately.


    Please let me know if there are any additional questions. Thanks!


    Best Regards,

    Brett Colteaux