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TPS23880: How can I limit the PSE power allocation to all classes (1...8)

Silvio Gehri
Prodigy 100 points
Part Number: TPS23880

I'm designing a PoE Passthrough device and need to limit the power at the PSE to one of the classes (1 ... 8).

Register 0x29 allows for classes 4...8. Class 3 can also be setup (2P or 4P). However, I don't see how to limit the available PSE power to class 1 and 2.

I'd appreciate your help on this. Thanks.

  • 0
    TI__Genius 15685 points
    Hi Silvio,

    Thanks for using TPS23880. Register 0x29 of TPS23880 can only limit the port to 15W at power on. If the connected PD is class 1 and 2, TPS23880 will limit the port power automatically to the class level of the PD. If you want to limit the port power to class 1 or class 2 not matter what class level the PD is, you can set 15W in register 0x29 and then change the PCUT value in register 0x1Eh to 0x21h after the PEn bit is set in register 0x10h. Please check the details in TPS23880 datasheet register descriptions for 0x1Eh to 0x21h. BTW, I am curious to know why you want to limit the port power to class 1 and class 2. Thanks!

    Best regards,
    Penny
  • 0 in reply to Penny Xu
    Prodigy 100 points

    Dear Penny,

    Thank you for your quick and detailed reply. As we are targeting a passthrough device that can be daisy-chained, every device receives some power class from its predecessor, for example class 3. In order not to overload the entire chain, and since the device consumes some power too, this device should reduce the exposed power class on its PSE port.

    Without an option to limiting to class 1 and 2, we most likely need to end up with class 3 and install a current limiter by using the policy register(s), I guess.

    Best regards,

        Silvio