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TPS2373: Detection & negotiation issues for higher power class

Pavan Patil
Prodigy 70 points
Part Number: TPS2373

Tool/software:

Hi,

We have a design with TPS2373 (schematic attached).

We are in the process of testing this with 2 PSE devices, first is Netgear (model - FS108P) POE switch and other is Phihong Hi-POE injector (model - POE90U-1Bt6-R)

Following are the observations 

1. When we test with the Netgear switch which is 802.3af compliant, we get the 48V output and some small 50mA load is able to be driven.

2. when we test with the Phihong injector, we are unable to get the output and the detection and negotiation loop continues repeatedly

3. when we test the phihong injector with other poe pd module (waveshare gigabit poe splitter), it is working and the poe splitter provides a 5V output that we use to power a development board.

so now the query is  

1.  what is it the difference between the detection and negotiation path of 802.3af and 802.3bt other than the configuration resistors?

2.  if the poe pd works for the lower power, by changing only the resistor combination, it could be made to work for higher power. Is this thinking correct?

3. we have not mounted the successive UCC2897 and corresponding components, will this affect the higher power detection?

Any help on this will be much appreciated.

Thanks & Regards,

Pavan

POE2.pdfPOE3.pdf

  • 0
    TI__Mastermind 37031 points

    Hi Pavan,

    The PoE team will start travel from tomorrow until Feb 4th. Sorry for the delay on the response and thanks for your patience.

    Best regards,

    Diang

  • +1 in reply to Diang Xing
    TI__Mastermind 37031 points

    Hi Pavan,

    Thanks for your patience.

    If you want to test TPS2373-4 without UCC2897, you need to add a voltage source to VC_IN. Also, you need to DNP D3201 for the test. If no VC_IN input higher than UVLO, TPS2373-4 will have start up failure and go into hiccup mode.  

    Besides, when without UCC2897, please make R3211 as 0 Ohm to offer the enough maintain power signature current.

    Best regards,

    Diang