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TPS23754: TPS23754EVM-383 circuit with 24V adapter (option 2 OR-ing) possible?

Mats Pedersen Jonassen
Prodigy 105 points
Part Number: TPS23754
Other Parts Discussed in Thread: TPS23756,

Hi,

I have looked a bit around in the TI forums but couldn't find a definitive answer to this; We have designed a circuit that is very similar to the circuit in the TPS23754EVM-383 (SLVU304C), the only big difference being that we have changed the adapter circuit so that it is very close to what is described in SLVA306A figure 6 (option 2, PoE priority).

Our plan was to have the possibility of having adapter voltage with both 24V and 48V, but testing this circuit we see that we cannot get 12V output from this circuit when using 24V adapter voltage. Only at around 28V and above will we get a stable 12V output. Of course when studying SLVU304C further it clearly states adapter voltage minimum is 33V, but I can't seem to find an answer to exactly why that is. Hoping you could help me with this, as we would like to know if it's possible to mod the circuit in any way to allow for 24V adapter voltage (adapter must be connected on primary side, preferably with PoE priority but that is not a must if it's not possible).

Would it for example be possible if we instead used the TPS23756 for this circuit? Or could we just add a resistor divider to PPD pin in some way?

Best regards,

Mats

  • 0
    TI__Mastermind 21320 points

    Hello Mats,

    Thank you for your question about using a 24V adapter in this circuit. 

    So my understanding is you have PoE at 48V and an adapter at 24V, and they will power a 12V output. 

    This is possible, but not with the EVM design. As you noted, the EVM is designed to operate with PoE bt compliant voltages. A new power converter design is needed if a wider input range is needed. The TPS23754 can still be used, but it will need a larger transformer, for example.  

    If you are interested in a TI Design, please contact your TI Representative to begin that process. 

    Please let me know if you have any additional questions or if I can clarify anything for you.

    Thank you!

    Regards,

    Michael Pahl