• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 62 subscribers
  • Views 467 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM3481MM Regulator Died Because CSD17559Q5 Stopped Working

Garrett Marshall
Prodigy 210 points
Other Parts Discussed in Thread: CSD17559Q5, LM3481, CSD18509Q5B

I used Webench to create a 24 VDC upconverter from 12VDC.  Over a couple weeks of running the upconverter stopped producing the 24VDC.  I initially replaced LM3481MM, but it still didn't work.  I then replaced the CSD17559Q5 Power Mosfet and the 24VDC upconverter started working.  It is concerning that the MOSFET died and I would like it to be analyzed to give me an indication if the issue was contained within the package of the MOSFET or if it is a board layout issue.

Thanks,

Garrett Marshall

  • 0
    TI__Expert 6165 points
    Hello Garrett,

    I work with the product line that builds the LM3481MM. If you would like any information concerning the LM3481, please let me know.

    Regards, Robert Blattner
    Robert.blattner@ti.com
  • 0 in reply to Robert Blattner
    Prodigy 210 points

    Hello Robert,

    I am going into production and would like to understand why the CSD17559Q5 stopped working.  Are there any other components that are equivalent to the  CSD17559Q5 that I could switch to that would make the regulator more robust?

    Thanks,

    Garrett

  • 0
    TI__Expert 6165 points
    Hello Garret,

    I have checked into characteristics of power MOSFETs and found:

    If you choose a device with BVDSS near your output voltage, it should have a repetitive avalanche rating EAR or IAR. Since there is parasitic inductance on your board, when the MOSFET switches off, there is a small spike in drain voltage. Devices with a repetitive avalanche rating can dissipate this energy safely – they can act as a Zener diode momentarily. If the device chosen does not have a repetitive avalanche rating, the ruggedness of the device while avalanching is not guaranteed. Most power MOSFETs have this rating. Note that an EAS rating is for a onetime event only.

    If you choose a device without an avalanche rating, you should leave enough extra rated voltage so that the device’s capacitance can dissipate the inductive spike. Normally this would mean a rating of 3/2 * (output(max) + diode drop). For your application this would be approximately 40 V using 3% output accuracy and a 1 V diode drop.

    Finally, most BVDSS specifications are at room temperature. Almost all devices have a positive temperature coefficient of breakdown with temperature – low temperature = lower blocking voltage. This should be factored in if operation while cold (-40C) is expected.

    The CSD18509Q5B has the necessary blocking voltage and a similar RDS. Its gate charge is ~1.5x but will most likely work,

    Regards, Robert

    PS. Have you been able to get an FA for your part?
  • 0 in reply to Robert Blattner
    Prodigy 210 points

    Thanks for the added information.  I will give the CSD18509Q5B a try.  We no longer have a TI Application Engineer in our area so I don't have any contacts to have a FW done.

    Thanks,

    Garrett

  • 0 in reply to Garrett Marshall
    Prodigy 210 points
    Hello Robert,
    I just wanted to let you know that we've been testing the CSD18509Q5B and it is holding up well. It appears that the device also runs a little cooler than the previous one that we were using. We are going to move to that part for the next build of boards. Thanks for all your help.

    - Garrett