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TPS2384: it doesn´t connect to an TPS2378 EVM-105 evaluation board

Thomas Jung10
Prodigy 70 points
Part Number: TPS2384
Other Parts Discussed in Thread: TPS2378, , TPS2378EVM-105, TPS23861, TPS23880, TPS2388

Wie have a 3 port midspan design with TPS2384 since several years. Now we had biult a new testing device containing the TPS2378 EVM-105 evaluation board.

Now we have the problem that our DUT with TPS2384 donst astbalish PoE connection with TPS2378 EVM-105 in about 30% of all tested ports.

But with other devices on the PD end it works fine as usual, e.g. LT4257 or LT4275 eval board or a PD with Silvertel PD.

Does someone have an idea abaut the issue with the inteconnction between TPS2384 and TPS2378 ?

  • 0
    TI__Genius 15655 points

    Hi Thomas ,

    When you say TPS2384 doesn't establish PoE connection with TPS2378EVM-105, do you mean the detection failed? Have you tried connecting TPS2384EVM to TPS2378EVM-105? Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    Prodigy 70 points

    Hi Penny,

    yes, i mean that the detection fails, some ports work, others don´t.

    Unfortunately we don´t have the evaluation module  TPS2384EVM. 

    Our product with the TPS2384  is in the market for about 10 years, since now with no problems.

    It was a coincidence that the problem occured.

    We had to rebuild our testing device. The new testing device contains  TPS2378EVM-105. Other PDs work fine.

    Best regards

    Thomas

  • 0 in reply to Thomas Jung10
    TI__Genius 15655 points

    Hi Thomas,

    I tested TPS2384EVM with TPS2378EVM-105 and actually the port can successfully turn on. Can you check if you see the green LED keeps blinking when you connect the PD EVM to your system? And did you use TPS2384 in auto mode? Actually the PD EVM doesn't generate enough current and if you use DC disconnect on the PSE side, the port will keep turning on and off. This can be solved by adding a load to the PD EVM. Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    Prodigy 70 points

    Hi Penny,

    the LED on the  TPS2378EVM-105 is not blinking. I also tried with DC load.

    The discovery is not successful, the TPS2384 is not entering classification.

    But reading former threads here on the forum gave a hint: The capacitor across the TPS2384 outputs is 220nF as suggested in the data sheet.

    When i remove the cap it works fine.

    What cap should i use? Currently there is a surface mount MLCC 220nF 100V in 1210 package

    best regards

    Thomnas

  • 0 in reply to Thomas Jung10
    TI__Genius 15655 points

    Hi Thomas,

    It is wired. Can you send me your schematic that I can take a look? Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    Prodigy 70 points

    Hi Penny,

    here is the requested schematics of our design.

    I dont know if the file is attached propely, and if you are able to open it.. otherwise please give me your email adress to send it.

     When we remove C3, C6 or C9 the effected port works fine.

    Best regards

    Thomas

  • 0 in reply to Thomas Jung10
    TI__Genius 15655 points

    Hi Thomas，

    My apologizes for the late reply. I checked with our design team that the port 0.22uF cap can't be removed as it could cause system stability issues without the cap. I found your 0.22uF cap is not directly connected between Pn and Nn. Have you tried to put the cap between Pn and Nn and see if the detection still fails? Thanks!

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    TI__Expert 5615 points
    Thomas, It has been ~ 1 week since your last reply. Do you still require our assistance with this thread or has your problem been resolved?
  • 0 in reply to Thomas Lewis
    Prodigy 70 points

    Hi Thomas, the problem is not yet solved, because i was working on another task.

    I will check asap.

    Penny´s  last hint concerning the position of the .22 capacitors seems very promising to solve the problem.

    As soon as i have a result i will write again.

    thanks and best regards

    Thomas

  • 0 in reply to Thomas Jung10
    TI__Expert 5615 points

    Thank you for the update!  And good luck...we are here for you should you need continued support.

  • 0 in reply to Thomas Lewis
    Prodigy 70 points

    Hi Penny, hi Thomas,

    unfortunately it doesn´t make a difference if i connect the cap directly to the P and N pins, or via the polyfuse.

    The affected ports only work properly if i omit the cap or reduce the capacitance to a maximum of 68nF.

    best regards Thomas

  • 0 in reply to Thomas Jung10
    TI__Genius 15655 points

    Hi Thomas,

    I think there might be some extra capacitance on the port. Our design team do suggest to keep the port cap 0.22uF, otherwise, it is possible to have system's stability issues. Removing the port cap is not recommended. Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    Prodigy 70 points

    Hi Penny,

    thank you for your support.

    We decided to stop further investigations on that issue because we are plannung a redesign in the near future.

    It only affects interoperability with TPS2378 and over the last years there were no complaints that our midspan board rejects some PSEs.

    best regards Thomas

  • 0 in reply to Thomas Jung10
    TI__Genius 15655 points

    Hi Thomas,

    It makes sense. So moving forward, I recommend TPS23861(4 channel, autonomous mode) or TPS2388(8 channel, semi-auto, I2C required)  for IEEE802.3at solutions and TPS23880 for IEEE802.3bt solutions. Please let us know if you need anything. Thanks.

    Best regards,

    Penny