• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 33 subscribers
  • Views 235 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:

Heating Problem on Power Over Coaxial on DS90UB913A

DS90UB935-Q1: Heating issue on D/S recommended inductors

Dhruv Lamba
Prodigy 60 points
Part Number: DS90UB935-Q1

Tool/software:

Hi 

We have noticed excessive heating on the ferrite beads in our POC network, to the point where one of them has burned. 

Please see the relevant schematic and layout section below:

There is a related bug from 2015 that did not get any response, but the symptoms seem quite similar. Our module is using 80mA which seems much below the spec of the ferrite bead.

Please let me know if I can share any other images/collateral.

  • 0
    TI__Mastermind 26410 points

    Hello,

    Thank you for your question. It looks like some of the components on your board are overlapping/exceeding the recommended manufacturing spacing. This could lead to manufacturing issues, especially if the landing patterns are not followed. The ferrite bead vendor can provide more details on the required landing pads of the ferrite beads. It would also be good to check that the traces carrying the power signal are wide enough to transmit the signal without increasing in temperature. The appropriate width will depend on your board, but if all traces are heating then that may be the issue.

  • 0 in reply to Darrah Merillat
    Prodigy 60 points

    Hi Darrah,

    The overlap you see is a user defined courtyard for layout and not the actual part. The components have plenty of room between them as you can see below:

    The traces are quite wide (0.4mm) with 35um copper. They are as wide as the pad basically.

    The burned ferrite beads are seen below: 

  • 0 in reply to Dhruv Lamba
    TI__Mastermind 26410 points

    There is likely a short or higher current/voltage being seen on the ferrite beads than intended. Note, that the current draw of an imager will fluctuate between active and blanking periods of the data stream. It would also be recommended to reach out to the ferrite bead vendor directly as they will be able to provide more details on the limitations and expected behavior of the ferrite beads.

  • 0 in reply to Darrah Merillat
    Prodigy 60 points

    Hi Darrah, 

    We are Xray inspecting the board to see if there are any shorts on the board. Regarding the density, we have compared our ferrite bead placement and it is quite similar to TI's EVK so we dont see any gross violation there. Furthermore, the Murata D/S doesn;t mention any minimum pitch, so I dont think we are in violation of that. 

    This could be thermal so we are checking that angle as well.

    Thanks,

    Dhruv

  • 0 in reply to Dhruv Lamba
    TI__Mastermind 26410 points

    Yes, these are good things to check. It would also be good to double check the current demands of the imager throughout operation.