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TPS23753A: PD off after start

Maksym Ka
Prodigy 40 points
Part Number: TPS23753A
Other Parts Discussed in Thread: TPS23753

I try to create PoE based on TPS23753A for my DIY project. I use http://www.ti.com/lit/an/slva305c/slva305c.pdf as start  point. 

I have 2 PSE -  Netis PE6105 and WS-C3560-48PS.

With WS-C3560-48PS all ok, board start and works without issues.

With Netis PE6105 board start, provide 3.3 V output but turn off after ~ 1 second. After that it start again, off in 1 second and repeat. 

I found strange behaviour - board able to start after preheating input circuit (bridge + tps23753) with hot air. 

I can't understand this behaviour. Some china cameras works without issues on this switch.

What i should check to resolve issue?

  • 0
    TI__Expert 5615 points

    Maksym,

    I will assign this thread to an Applications Engineer for further guidance; however, I first want to make you aware of the PoE logo program that is intended to minimize situations like this moving forward.  Through the EA, the industry is rolling out a PoE logo which will make it clear that a piece of end equipment (load or supply) has passed interoperability testing.  I encourage you to consider this program for your own projects moving forward and to make any switch vendor offering a troubling model aware of it.  You can learn more about the program via our E2E FAQ on the topic located here -->  .

    Our Application Engineer will follow up with you shortly to aid your efforts further.

    Thank you for considering PoE products from Texas Instruments,

  • 0 in reply to Thomas Lewis
    TI__Mastermind 40720 points

    Hi Maksym,

    Can you try adding a load to your 3.3V output to see if the cycling goes away? It's probably MPS as described in the datasheet. Thanks!

  • 0 in reply to Darwin Fernandez
    Prodigy 40 points

    Loading didn't change nothing. You can see below behavior with 1A load (3.3 Om resistor):

    CH1 (yellow): GATE pin

    CH2 (blue): VDD

    All measurements related to RTN pin.

    Start and stop with PSE SW-1:

    With another PSE all works:

  • 0 in reply to Maksym Ka
    Prodigy 40 points

    I try to understand who break power - TPS23753 or PSE.

    I measured levels on VSS and RTS pin related to VDD. It looks like PSE power off PD. 

    CH1 - VSS

    CH2 - RTN

    Start:

    stop:

  • 0 in reply to Maksym Ka
    Prodigy 40 points

    CH1 - Vdd

    CH2 - RTN

    Related to Vss

  • 0 in reply to Maksym Ka
    TI__Mastermind 40720 points

    Hi Maksym,

    Can you forward your schematic so we can review it? At first glance looking at your waveforms, the gate looks like it is pulse skipping and it could be that the current is low enough from the PSE prospective to remove power. 

    Also have you tried ordering a TPS2753AEVM-004 just to see how it behaves with that specific PSE?

    Lastly the waveform helps slightly but can you take something similar to figure 16 of the TPS23753A datasheet (in DC coupling and not AC)? Thanks!