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Output Voltage Range of PoE controllers with built-in DC/DC converters

Johnny T
Prodigy 10 points
Other Parts Discussed in Thread: TPS23754

Hi.

I'm normally not designing power-related circuitry, but now I'm considering the using the TPS23754 in a design. I have tried to read the spec, but I'm still not sure about the output levels and how it's adjusted.

I need to generate a +24V system voltage (1A max current), from the ethernet cable. Is this voltage level achievable, and what transformer should I use?

I'm planning on implementing this feature on a Gigabit LAN. Do you seee any problems with that?

  • 0
    TI__Expert 7990 points

    In general, power supply design is very difficult for novices, so I would caution this information is of limited usefulness to you.

    The TPS23754 is a combination PoE+ interface and dc/dc controller.  The actual output voltage is the result of the rest of the power supply and is not restricted by the TPS23754.

    IEEE 802.3at is compatible with 1000baseT.

    The power available to the PD per IEEE 802.3at is 25.5W. assume that you will get an efficiency on the order of 88% (just a guess) to estimate the available output power.

    In short, I suggest that you look at   http://focus.ti.com/docs/toolsw/folders/print/tps23754evm-420.html (or search the TI webpage for slvu301) and http://www.coilcraft.com/poe300.cfm .  Coilcraft has a verision of the transformer designed for 24V.

    There are lots of other changes to the SLVU301 circuit that are required apart from the transformer.  You might look at SLVA305 for some design hints, and search the TI website as well for past Unitrode and TI papers on flyback design.