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TPS2378: Power Drop Issue

Nick Nabors
Prodigy 20 points
Part Number: TPS2378
Other Parts Discussed in Thread: TPS2375EVM,

I am attempting to use PoE to power my design (board powered by DCDC needing power from PoE) but the PD power shuts down when I connect the power out from the TPS2378EVM-105 to my design (after I allowed the CDB to show setup complete). I have successfully done this with the TPS2375EVM but not with this part (TPS2378EVM-105). With the TPS2375EVM, I can set the class to 0 on that EVM and all runs well. I have noted that for the TPS2378EVM-105, it is only hard set to Class 4. It powers up when I connect it with only 4.7kΩ as the load, like the other TPS2375EVM, but when I connect my design board to it, the output drops to 800mV. I tried Class 4 on the TPS2375EVM to imitate this scenario and the same thing happens.

Theoretically, would I have to load up to 12.95W to have Class 4 work? Are the ranges in this table for load wattage "up to the value" or from "minimum load needed to maximum load allow"? Any help would be greatly appreciated.

Thanks,
Nick

  • 0
    Prodigy 20 points

    My design runs from 24-60V and uses ~33mA-77mA on average and up to ~500mA-600mA (if some other components are attached).

  • +1 in reply to Nick Nabors
    TI__Expert 7870 points

    Hi Nick,

    TPS2378EVM doesn't have minimum power requirement at class 4. 12.95w-25.5w is just recommended range for class 4.

    It looks like you will face the same power down issue when TPS2375EVM and TPS2378EVM is at class 4 in your setting.  I will suggest to check whether your PSE injector can support class 4 classification or check whether the VDD of POE injector waveform drop at load connected.  Thanks.

    Regards,

    Ben