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TPS2376: Non expected waveform in the PoE lines

Nasib Fahim
Prodigy 90 points
Part Number: TPS2376

Tool/software:

Hi there, i am using your TPS2376PW device with this configuration: 



When i connect the Ethernet cable through an PoE inyector (TL-POE150S) i got this waveform measuring VDD-VSS:



I suspect there i am seeing the Detection voltage ( 3.8V) the classification voltage (7.8V) and the power delivery voltage (48V) . 

My questions: 

* Is the above correct? 

*  Why the classification voltage is so low? 

* Why the system is reseting after supplying 48V? 


Thank you so much. 

  • 0
    TI__Mastermind 37101 points

    Hi Nasib,

    Thanks for reaching out!

    The "classification" voltage looks lower than it should be. I think it may be actually the detection voltage which is 2.8 -10 V.  CLASS pin only output correctly when VDD-VSS is higher than 10.2V. 

    One thing I noticed is that you have a low UVLO resistance. In TPS2376HEVM, the total UVLO voltage divider resistance is ~1M Ohm so that the detection and classification signatures won't be influenced too much. 

    For the system restarting. It may be related to loss of maintain power signature if you did not connect a load on the downstream. Please make sure if you have >10mA current flow from the PD interface.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Prodigy 90 points

    Solved: the system required a minimum power consumption to maintain the voltage. 

    Thank you for your support. 

  • 0 in reply to Nasib Fahim
    TI__Mastermind 37101 points

    You are welcome Nasib!