• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 390 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.

LM5122: LM5122 : The MOSFET over stress under the start up.

Rock Shao
Expert 2995 points
Part Number: LM5122

Tool/software:

Hi,

My customer found the MOSFET issue during the startup.

Boost uses TI LM5122 (Input:-48V, Output: 80V). The wiring is as in the attachment.
Currently, in factory production, Boost MOS breakdown occurs during startup. Some abnormal waveforms have been measured as follows.

Vds waveforms

Vgs and Vdc waveforms

And please help to check the schematic and Layout, thanks.

CDD452A3-F560-V02.pdf
CDD452A3_SCH.pdf

  • 0
    TI__Mastermind 30390 points

    Hi Rock,

    Thanks for using the e2e forum.

    Looking at the waveform, this hiccup behavior may be related to the softstart time and not a malfunction.
    If a very short softstart time is chosen, the device may trigger overcurrent protection during startup, which resets the device, leading to a hiccup behavior.
    My first suggestion would be to increase the softstart capacitor (C35) until the device can start up with a smooth, continuous ramp.

    For the second picture, I assume customer is concerned about the strong voltage overshoot.
    I cannot say just now why only one strong overshoot occurs while the switching looks normal before this event.
    If they see continuous overshoots of the switch note, they may try increasing the gate resistance or adjust the snubber values of the RC filter (R18/C13).

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Expert 2995 points

    Hi Niklas,

    The Customer had an LLC after the LM5122, and we found that output dropped when the LLC started at 72V.

    We fine-tuned the comp pin C36 but no more improved. and I checked the schematic, and the MODE pin was flooring. should we pull this to Vcc?

  • 0 in reply to Rock Shao
    TI__Mastermind 30390 points

    Hi Rock,

    The LM5122 will always start up in DEM mode, independent of the MODE pin connection. Once startup is finished, it will switch to the according setting.
    If MODE pin is floating, the device will run in DEM mode per default. You can connect the MODE pin to VCC to set it to FPWM mode to check if the behavior improves.
    However, this will not affect the hiccup behavior at the ramp up, as this should be related to the softstart itself.

    Best regards,
    Niklas