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Original question:

TPS2373-4EVM-758: Zener Diode

UCC2897A: PoE Zener Diode Getting hot

Mike Oudshoorn
Prodigy 30 points
Part Number: UCC2897A
Other Parts Discussed in Thread: TPS2373, , TPS2372

Tool/software:

Dear TI,

I was asked to ask my question here. I'm having some problems implementing the active clamp forward design with the PoE chip TPS2373 and the UCC2897A. I believe that the UCC is in a hiccup mode. Can you please help me solve this issue.

Link to previous post

Schematic:

3247.Hubbay-PoE PD.pdf

  • 0
    TI__Guru 73645 points

    Hi,

    What do you mean UCC is in hiccup mode? What is "UCC", what do you mean hiccup?

  • 0 in reply to Hong Huang
    Prodigy 30 points

    Hi Hong Huang,

    Sorry for the confusion. I used the TPS2373 as a reference design. The output voltage of this system should be 5V. Its now 1,3V. I noticed earlier with a thermal camera that D5 was getting very hot. I also could here an audible switching sound. I couldn't find the issue so i contacted the TPS2372 team.

    I measured the gate voltages of the FET's and it looks to be normal.

    Then I measured VCin and VCout. 

     

    Green is VCIN; Blue is VCOUT; Yellow is VDD.

    Could you please help me figure out how to fix this issue.

    Kind Regards,

    Mike Oudshoorn

  • 0 in reply to Mike Oudshoorn
    TI__Guru 73645 points

    Hi,

    Please provide your schematics.

  • 0 in reply to Hong Huang
    Prodigy 30 points

    Dear Hong,

    See the main post of this thread. the schematic is added

  • 0 in reply to Mike Oudshoorn
    TI__Guru 73645 points

    Hi,

    Both VCIN and VCOUT are TPS2373 in and out. So for this issue, a typical approach to debug is to separate UCC2897A from TPS2373, i.e., disconnect VCOUT from UCC2897A, then provide a 14V external bias to UCC2897A VDD through a diode to test UCC2897A converter to make UCC2897A converter work normal first. If UCC2897A converter with external 14V bias works ok. Then the issue is not from UCC2897A but TPS2373. Then you need to talk to TPS2373 team to support. I am not familiar with TPS2373.