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TPS2378: TPS2378 +TPS54360 Poor power supply

user5157625
Prodigy 120 points
Part Number: TPS2378
Other Parts Discussed in Thread: TPS54360, , TPS2372, TPS2373, TPS23880, , UCC2897A, PMP20859

hi  sir/madam,

   

Now I have made a router case, using POE power supply (TPS2378+TPS54360), the power is greater than 30W. Now I use two TPS2378+TPS54360 to power the system. Now the following situation appears:

1. When I use the switch to supply power to the router, first I plug in one portPOE&PSE.pdf and the power is normal. When I plug in RJ45 to supply power to another port, the system will lose power, and the power will be recharged at a interval of 2 seconds

2. This will not happen when I use two switches to supply power to two ports. When the two switches were connected together, there was a situation like 1.

Attached is the schematic diagram, please help to see if there is any change to improve this situation, thank you ~~~

  • 0
    TI__Expert 5615 points
    I will allow our PD Application Engineer to answer your question as written here, however, I wanted to make sure you are aware of the new IEEE 802.3bt standard which was recently ratified and allows for a much simpler (and inter operable) implementation of PoE for power requirements exceeding 25.5W at the input to the load (PD side).

    You can learn more about the new standard via our training portal here --> training.ti.com/power-over-ethernet-getting-started-new-standard (complete with a great whitepaper and easy-to-learn-from videos).

    The IC solutions available for such an implementation are the TPS23880 (PSE side) and TPS2373 / TPS2372 (PD side).

    I encourage you to look into those solutions to see if they can't offer you benefit far exceeding those of the TPS2378 variety.

    Thank you for your interest in PoE solutions from Texas Instruments,
  • 0 in reply to Thomas Lewis
    Prodigy 120 points

    Hi   Thomas Lewis,

       We have assessed TI's tps2373-4 in the new case, but the previous case used two TPS2378 for power supply. Could you help solve this problem? Thanks!!!

  • 0 in reply to user5157625
    TI__Expert 5615 points
    That's good to hear - thank you.

    Our PD Application Engineer, Tom Amlee, will respond within 24 hours to your TPS2378 question.

    Thanks,
  • 0 in reply to Thomas Lewis
    TI__Genius 9230 points

    Hi User,

    In order to successfully detect & classify on the 2nd port, the RTN pins cannot be connected together because the diode bridge of the 2nd port will be reverse biased. See TPS2378EVM-602& the associated non-standard forced 4-pair app note, slva625a, for more details on how this is implemented.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Prodigy 120 points
    Hi TOM,
    Both of these two reference designs are two TPS2378+ one UCC2897A, which is the isolation scheme. Is it ok for the customer to use two tps54360 for non-isolation now? Looking forward to your reply, thanks!
  • 0 in reply to user5157625
    TI__Genius 9230 points

    Hi User,

    The TPS54360 can be used. The circuit for controlling the gates of Q8 & Q9 can be simplified & redesigned to use a single BJT instead of an optocoupler (U7) circuit because isolation is no longer a requirement. 

    Regards,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Prodigy 120 points

    hi  TOM

      In addition to Q8&Q9, where else do we need to optimize, and how do we solve the problem of power loss in the second port,thanks

  • 0 in reply to user5157625
    TI__Genius 9230 points
    Hi User,

    After further review, it appears that the 2nd port is unable to power on because the 2nd PD cannot complete inrush when both ports are connected to the same PSE.

    While the 1st port is supply power to the switcher, the 2nd port is attempting to charge its input capacitor, but cannot because the inrush current is going to power stage, instead.

    We encountered this while developing PMP20859. We got around this by adding a load switch with a delay circuit to each PD's RTN to allow the 2nd plugged in port to finish charging the input cap without the inrush current going into the currently operating power stage. We had to leverage the inrush delay enable pin on the TPS2372 to implement the delay circuit. This cannot be done easily with TPS2378.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer