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TPS23880: PoE Architecture Question

Brian Angiel
Expert 3700 points
Part Number: TPS23880
Other Parts Discussed in Thread: TPS23881

I am implementing a POE solution using a TPS23880 PSE. I am using 2 of the ports to implement a 90W PD connection. I also have four 15.6W PD in other parts of the board. I am having issues putting together a power supply that outputs 56V @ 3A that does not use a heatsink, so I split the power supplies into one for the 90W and one for the four 15W (62W or so). The problem I am now seeing is that the VPWR line probably wants the power that is being sent to the Ethernet connector and I have 2 powers. Is it best to then set up two separate PSE devices or can the 8-port one be used for both even though the VPWR would only be connected to one of the supplies? I have a feeling I know the answer, but had to ask.

Thanks,

Brian

  • 0
    TI__Genius 15685 points

    Hi Brian,

    It is OK to set up 2 PSE devices and connect them to 2 power supplies and you can connect I2C buses together to host, but it is a little expensive. If you want to split the power input to 2 power supplies and use one PSE device, it is also doable as long as you control the output voltage of the 2 power supplies and make sure they share the load. 

    In addition, TPS23881 is a newer device with autonomous mode, reduced Rsense and capacitance measurement. It is pin to pin compatible with TPS23880. You may consider switching to TPS23881. Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    TI__Expert 3700 points

    I think my problem is that there is no way to guarantee that the load will be shared. One of the supplies was to supply a device that will always be on and pulling about 50W. The other supply was to power the 4 independent POE ports that could have 4 15W devices on it or none on it. Is that a bad way to set up the system? I wanted one supply to supply them all but the amperage and 55C temperature were causing heatsinks that we don’t have room for. That is why I split them onto separate power lines.

    Are you saying that I can merge the output of the two supplies together into one? That seems a little scary to me. Would they regulate off of each other? How would I know that they are sharing the load?

    Brian

  • 0 in reply to Brian Angiel
    TI__Genius 15685 points

    Hi Brian,

    I have seen some power supplies can be used in sharing mode and they may sense each output and adjust the output to make sure they are balanced. We have been using RFE250048 for sharing mode power supply to test our system level software. IF that's too complicated for you, you can just use 2 PSE devices. Thanks.

    Best regards,

    Penny