• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 436 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS23861: TPS23861 overcurrent setting

Jerry Hsu3
Prodigy 150 points
Part Number: TPS23861

Hi Team

I'm planning to design the schematic following Figure. 49 in the datasheet, but I don't want to reserve the fuses.

How should I set the overcurrent condition if I2C connected to the ground as like Figure 49?

  • 0
    TI__Expert 3700 points

    Hello,

    Thank you for your question. The PoE applications engineering team is currently out of the office celebrating U.S. holiday and will return tomorrow, Tuesday 12/29. A response will be provided to this post tomorrow once the team is back. Apologies about the delay and thank you for your patience.

    Best Regards,

    Brett Colteaux

    PoE Product Marketing Engineer

  • 0 in reply to Brett Colteaux
    Prodigy 150 points

    Hi Team

    I'm not sure what the function of J17 in the reference design of TPS23861EVM-612 is.

    Just attach my schematic. Please also help me confirm it, thanks.

  • 0 in reply to Jerry Hsu3
    TI__Mastermind 41770 points

    Hi Jerry, sorry for the delay as we're back from winter holiday. J17 is just header of the motherboard. Majority of PSEs will use a motherboard/daughtercard approach. It allows for a 4layer motherboard (RJ45, data transformer etc, microcontroller) since it is part of the total system PSE hardware, and a 2layer daughter card for a lower total system cost. This also allows flexibility from using 2 pair or 4 pair PSE controllers by switching out the daughtercard without re-laying out the PCB.

    A couple of comments regarding the schematic:

    At the data transformer for each of the pairs, the return path should not connect to GND but rather the drain of the PSE pass FET. Please see the EVM as an example. Otherwise, the voltage on the port will always be 54V and no PoE handshake would occur.

    Also please make sure for the power sequence, that VPWR powers up before VDD. This is required per the datasheet. You can also use the EVM as an example.

    Thanks!

  • 0 in reply to Darwin Fernandez
    TI__Mastermind 41770 points

    For the question regarding the fuses, the fuse is NOT a required component for the PSE to function correctly. It is more a system level option for added protection and to get UL certified without validation testing.

    For the overcurrent question, since the TPS23861 is operating in automode, and not using I2C, the PSE will automatically adjust its overcurrent threshold based on the negotiated power of the PD. So if a Type 1 PD is connected, the PSE will protect itself when the power reaches over 15W.

    Thanks!

  • 0 in reply to Darwin Fernandez
    Prodigy 150 points

    Hi Darwiin

    Thanks for your response.

    I revise my schematic following your suggestion. Please kindly help me confirm whether I comprehend what you said.

    In addition, how should I handle with I2C(SCL/SDAI pin) to confirm that  TPS23861 is operating in automode properly? Pull to VCC/GND or left floating?

  • 0 in reply to Jerry Hsu3
    TI__Mastermind 41770 points

    Hi Jerry, the schematic looks okay to me. For the I2C we use the below reference design in automode as well. We pulled SDAI and SCL LOW, then kept SDAO floating. Thanks!

  • 0 in reply to Darwin Fernandez
    Prodigy 150 points

    Hi Darwiin

    Thanks for your response.

    One more question, if I want to disable TPS23861 for power saving, do you suggest using host control to assert RESET or SHTDWN pin at a low level?

  • 0 in reply to Jerry Hsu3
    TI__Mastermind 41770 points

    Hi Jerry,

    The shutdown pin only shuts down select ports while RESET pin shuts down all ports. If trying to shutdown ports to reduce the power consumption of the power supply, I recommend using RESET LOW. Thanks!