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TPS23881: TPS23881 circuit review.

Part Number: TPS23881
Other Parts Discussed in Thread: LM5574, , , LM5019, TPS7A4001

Hi Sir:

Attach BT POE injector circuit. Please assist review it.(Please see the below)

Thanks!

  • Vmain= 54V input DC voltage
  • VDD3_3V_PoE=3.3V DC voltage(use TI LM5574 IC=>54V to 3.3V)
  • Two RJ45 port
  •  LAN transformer pin define below.

By the way! Can I upload PDF file directly?

Sorry! The captured picture not clear.

Caspar Lai

  • Hi Caspar,

    It looks like you want to have a RJ45 port and each port can output 60W without any host control. 

    If my understanding is correct, you will have to use 4 channels of TPS23881 since one 4 pair high power port need to use 2 PSE channels. Please refer to TPS23881EVM-008 and PSEMTHREVM-007 for reference. In this EVM kit, channel 5-8 are designed to support two 4 pair ports. 

    You can upload your PDF to this thread by clicking insert file button. 

    In addition, since LM5574 doesn't support adjustable UVLO, it is recommended to use LM5019 and set the UVLO to ~30V. Thanks.

    Best regards,

    Penny

  • Dear Penny:

    Sorry, Maybe I didn't describe it clearly.

    I want design one port PSE injector product.(only one RJ45 port provide POE 60W output)

    Please see the application drawing below.

    I already reference for "TPS23881EVM-008"+"BOOST-PSEMTHR" EVB circuit.

    ould you assist verify POE circuit(please see last post)?

    Please especially focus IC (U2)peripheral circuits and connecting LAN transformer(T2) pin traces.

    Please assist. Thanks!

    Caspar

  • Hi Caspar,

    The schematic looks good overall, but please follow the datasheet for unused port connection. If you want to add test point for I2C bus, you will also add the test point at SDAO. 

    For the data transformer, please make sure it can handle the current level you need. 

    If you would run type 4, 90W, please make sure the polarity meets IEEE standard below.

    Thanks,

    Penny

  • Hi Penny:

    Thanks! Follow your suggest.
    I already modify some circuit. Please see the below.

    Modify list
    1. unused port "SENx" and "DRAINx" pin connect to ground
    2. Pin 21/46/57 connect to ground

    If the circuit have any wrong. please let me know.
    Thanks!

    Caspar

  • Hi Caspar,

    Please make sure you do the following check:

    1. Change the  LM5574  to LM5019 and set UVLO to ~30V
    2. Please make sure the data transformer can handle the current level you need
    3. If you would run type 4, 90W, please make sure the polarity meets IEEE standard.

    Other than these, everything looks OK. Thanks.

    Best regards,

    Penny

  • Dear Penny:

    Thanks!

    About your item 1=>Change LM5574 to LM5019.

    We already design LM5574 in many other product.(54V to 3.3V).

    Could you let me know your consider?  

     Thanks!

    Caspar

    Kǎolǜ
    consider
  • Hi Caspar,

    It is best practice to keep RESET pin low before Vpwr reaches UVLO(26.5V). Since there's no host control in your design and RESET pin is internally pulled up to VDD. We need to keep VDD low before Vpwr reaches UVLO(26.5V). You can use LM5019 or TPS7A4001 with adjustable UVLO to have a controlled VDD. Thanks.

    Best regards,

    Penny

  • Dear Penny:

    Got it! Thanks for your suggest.

    This issues close.

    Thank you again.

    Caspar