• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 914 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.

Original question:

TPS2378: The APD internal resistor

TPS2378: The APD enable issue

chentsu chung
Mastermind 6180 points
Part Number: TPS2378

Hi,

Our customer try to use external adapter and enable APD, but sometimes they found APD doesn't work even Vapd rise above 1.5V.

MayI know is there any possiblity that APD doesn't work even Vapd rise above 1.5V?

Thank you.

C.T.

  • 0
    TI__Genius 9230 points

    Hi CT,

    1. Is this adapter meant to work with 24Vac & "28Vdc to 58Vdc" adapter noted on the schematic? Which adapter input is the customer using when they are unable to get the APD signal working?

    2. Is the "SMAJ58A" on the output of the LDO populated?

    3. Is there a special reason why they are using a zener with an LD instead of a simple resistor divider like in the Figure 1 schematic SLUA477? Is it to accommodate the 28V-58V DC voltage range?

    http://www.ti.com/lit/an/slua477/slua477.pdf
     
    Regards,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Mastermind 6180 points
    Hi Tom,

    For your question:
    1. In this case is 24VAC only

    2. Yes, this is for voltage spike prevention. Sometimes the voltage spike comes out when external adapter inserting during the operatoion of PSE, and "SMAJ58A" can prevent APD pin from damage.

    3. Actually, this curcuit is leveraged from UPOE schematic. In order to prevent TPS2378 from voltage spike when external adapter hot-swap, so use the voltage clamping circuit as Zener and LDO.

    Before looking at the schematic, could you please let us know:
    1. If want APD function working, what condition should be satisfied? Only APD to RTN >1.5V?
    2. Is there any possiblity that APD doesn't work even Vapd rise above 1.5V?


    Best regards,
    C.T.
  • 0 in reply to chentsu chung
    TI__Genius 9230 points

    Hi C.T.,

    Remove the TVS diode on the output of the LDO & see if you can attain the proper voltage on the APD pin.

    You only need to get APD > 1.5V.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Mastermind 6180 points
    Hi Tom,

    Thanks for your response. Besides, could you please let us know:
    1. If want APD function working, what condition should be satisfied? Only APD to RTN >1.5V?
    2. Is there any possiblity that APD doesn't work even Vapd rise above 1.5V?

    This is what we want to know in this thread. We will check the TVS and LDO performance, but before this, we need to know the exactly mechanism of APD then can help us in debugging. Is need only 1.5V satisfied? Or anything inside TPS2378 also affect APD? Please help us to know these 2 question, thank you.

    Best regards,
    C.T.
  • 0 in reply to chentsu chung
    TI__Genius 9230 points
    Hi C.T.,

    1. To use APD, meet the APD voltage thresholds specified on page 5 & do not exceed the max APD voltage specified on page 4. Nothing else inside the PD controller affects APD.
    2. If APD does not work under these conditions, I would encourage the customer to order another IC.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer
  • 0 in reply to Thomas Amlee
    TI__Genius 9230 points
    HI C.T.,

    Was I able to answer you question? If so, could you click the green "resolved" button? I will be closing this thread now. If you need additional support, just reply. The thread will be reopened.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer
  • 0 in reply to Thomas Amlee
    Mastermind 6180 points
    Hi Tom,

    Yes, Thank you very much.

    Best regards,
    C.T.