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TPS2378: PoE USB charger & LED lights

howard banks
Intellectual 580 points
Part Number: TPS2378
Other Parts Discussed in Thread: TPS2511, TIDA-01463, TPS54560

I am looking to develop a simple USB charger that is powered over PoE.

I have identified the TPS2378 as a suitable PD Interface.

USB charging will be controlled using a TPS2511.

My question relates to the buck switcher i will need to take the PoE voltage (after the TPS2378) and drop to 5V for the USB supply. Does the switcher need to be an isolated design? My thought is yes, as it accessible by third parties? Is this correct?

Another project on the back burner is to provide LED lights powered from PoE. As there are no accessible parts, i presume any switchers i utilise in this design wouldn't need to be isolated?

  • 0
    TI__Genius 9230 points
    Hi Howard,

    The converter does not necessarily need to be an isolated design, but it will depend on your end application. If you would like help selecting your DC/DC converter, take a look at our Webench design tool: www.ti.com/.../overview.html

    I am not sure what you mean by "accessible by third parties". Could you explain?

    We are about to release a non-isolated PoE LED Lighting Ballast TI Design soon using the TPS2372-4. Be on the look out for TIDA-01463 in a few weeks. I may be able to share the reference design with you right away, if you message me privately :)

    Thanks,
    Tom A.
  • 0 in reply to Thomas Amlee
    Intellectual 580 points
    Hi Tom,
    The PoE USB charger will become part of our product portfolio.

    By its nature, the USB socket used for charging is readily accessible by anybody (my term third party). This made me wonder whether the switcher should be an isolated design. Initially i was looking to use a TPS54560 to provide the 5V, which id like to keep if an isolated switcher isnt required.

    Howard
  • 0 in reply to Thomas Amlee
    Prodigy 125 points

    Hi,
    I am confused in the same area.
    1. I would like to know, Whether using a non isolated converter (- LED Driver) at the PD side would be against .BT standards PoE isolation requirements.
    2. I am thinking of using the same TPS2372-4 . If possible kindly share the ref design with me as well.

  • 0 in reply to arjun raj
    TI__Genius 9230 points
    Arjun,

    1. A non-isolated converter does not violate the PoE .BT standard. In fact, the .bt standard was partly created with a non-isolated LED ballast application in mind. Typically we see PoE designs with non-isolated buck converters at type 1 power levels because conducted emissions and ripple are more manageable. Example: www.ti.com/.../tiduas7.pdf

    2. I will share it with both of you in time. I'm get the design past compliance process. Search for "TIDA-01463" in a few days to weeks.

    Thanks,
    Thomas A.
  • 0 in reply to Thomas Amlee
    TI__Genius 9230 points

    The PoE Lighting TI Design has been released!

    http://www.ti.com/tool/tida-01463

  • 0 in reply to Thomas Amlee
    TI__Genius 9230 points
    Arjun & Howard,

    To address your concerns about whether a non-isolated topology is compliant with the .BT standard, let me quote the great Darwin Fernandez (our PD expert):

    "Generally speaking, the IEEE wants the ethernet network isolated from all other potentials, and also from high-surge environments. The safety rules treat the ethernet like a telecom potential and have requirements for eliminating personal exposure to hazardous telecom potentials including direct touch and metallic interfaces exposed to the telecom potentials.

    The IEEE standard covers operational requirements. The safety rules usually come from EN/UL/IEC 60950-1. Ethernet is usually treated like a TNV voltage. Requirements are spread throughout the standard, with section 6 specific to telecom equipment.

    We have seen both isolated and non-isolated solutions. In general, when the end-user has no physical access to the internals of the end-equipment (completely enclosed to the outside world), then a non-isolated converter is probably okay and the safety engineer is usually consulted to make that decision. Many safety-conscious designers use the isolation when in doubt to be "safe".

    For USB solutions in PoE solutions, all designs I’ve seen are isolated.

    For lighting, since the lighting ballast is fully enclosed, it is expected to be a non-isolated solution. However, in some designs there are optional output connectors (sensors that are not integrated in the end equipment and enclosed) of these lighting ballasts. In this case, the design is isolated. "

    Howard, if you have more questions about the 5V isolated switcher you plan to design with, I highly recommend posting in the part's associated E2E forum where you can talk to USB experts, directly.

    Good luck,
    Thomas A.