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TPS23861: A question about PoE PSE TPS23861

Andy Liu3
Intellectual 2500 points
Part Number: TPS23861
Other Parts Discussed in Thread: TPS23754,

I am the FAE of Inspur Group, a leading server and cloud computing provider.

Recently, my customer is evaluating our PoE products, and the attachment is schematic, TPS23861 as PSE, and TPS23754 as PD.

 

A question of their feedback made me very confused, so I want to ask for your help.

The PSE board they designed does not enter the overcurrent protection even after the load exceeds 31W.

and I find the IEEE 802.3at(PoE plus) stipulates the PSE output need <=30W, TPS23861 can match the PD load automatically according to the IEEE 802.3at.

 

So what might be wrong, TPS23861 can output 31W power? Is there any problem with the customer's circuit design, could you help review the schematic diagram, thank you.

How does the protocol ensure that the output power of TPS23861 does not exceed 30W, and what will happen if it exceeds 30W?

Best regards,

Andy Liu0257.PD.pdfpse.pdf

  • +1
    TI__Mastermind 41800 points

    Hi Andy,

    Is customer operating in semi auto mode or automatic mode? If semi auto, are they setting the current for AT power?

    For the hardware, can you make sure the sense resistor is rated for 1/4W? Also the sense resistor trace with KSENSE pin should be kelvin sense lines for the layout. Can you double confirm. Lastly can you make sure the port voltage is accurate by reading the register value and checking with the multimeter? This is since i notice 50 ohm resistsor on drain pin instead of 47 ohms. 

    Lastly can you double check that sense pin and drain pin voltages are not noisy?