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TPS2373: Voltage glitch on switching between PoE and DC power supply

Part Number: TPS2373
Other Parts Discussed in Thread: PMP20859

Hi team 

We  are  using TPS2373-4. in one  of  our application. We  are  observing  Glitch in 5V output  power whenever  we  are  switching  from DC  to  POE  supply.  Our  Output  requirement is  5V @13A current .

Please  let  me know  if  i can  avoid  the same  somehow. As  per my  understanding whenever  we  switch bet  two power  source  APD  takes  time to  drop  below  threshold and before that power  goes down.

How  i can avoid  same.    

  • Hi Team 

    We have  following  further  observation 

    1) Issue  always  comes  when we are  switching from DC  to  PoE. Once  issue  comes  system  doesn't  work even if  we  switch  it  back  on DC  power  source. 

    2) Seems  like  internal Mosfet  inside  PD  controller  is  not  connecting  RTN and VSS . As  per my  understanding  this  should be  connected  during PoE power  source. Please  confirm if  our  understanding is  correct  ? 

    3) Please  suggest  how  we  should  proceed  with debugging.

  • Hello,

    Thank you for your questions. 

    1. Could you please share what is the adapter voltage used?

    2. Your understanding is correct, the internal FET should connect to RTN and VSS during PoE power. 

    3. Could you please share your schematic with me? Is your design referencing PMP20859? 

    As FYI - To enable a transition from AC/DC adapter to PoE without a drop of power on the load is what we refer to as a "hitless transition." We have a very detailed explanation how to obtain hitless transition in the video here: Designing dual-input PoE PD systems power redundancy, smooth transition, and power sharing applications.

    I understand that your application only has one PoE input and as a heads up this video details how to design dual inputs with hitless transition. However, the same principles discussed in the video can be applied to your single PoE port application.

    Please feel free to watch this training material which I think will help and let us know if you have any additional questions. Thanks!

    Best Regards,

    Brett Colteaux

    PoE Product Marketing Engineer