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LM5140-Q1: Important heating of MOSFETS, dead time issue ?

Clément Letonnelier
Expert 2796 points
Part Number: LM5140-Q1
Other Parts Discussed in Thread: LM5143-Q1

Hello,

We implemented the LM5140 for + 3V3 @ 1A and + 5V @ 1A from 28V
Today the Mosfets transistors are heating up enormously. We do not understand

Here is our schematic:

Here is what we observe on the VDS of the transistors (HS Blue / LS Green):

Best Regards,

C. Letonnelier

  • 0
    Expert 2796 points
    As you can see from the above oscilloscope screenshot, dead time doesn't seem respected and we suspect the heat issue could come from there.

    We are wondering if an incorrect PCB routing could be a reason ?
    Indeed, we have connected PGND1 and PGND2 to our ground plane instead of connecting it close to the MOS as it is suggested in the datasheet.

    Clément
  • 0 in reply to Clément Letonnelier
    TI__Guru 73652 points
    Hi Clément,

    If the high-side and low-side gate voltages are overlapping, try removing the gate resistors of the low-side FET. Also, I advise filling out the quickstart calculator available by download from the product folder. You can use the LM5143-Q1 version as it has more capability in terms of power loss calculations. For a 28V input, you may be able to operate with 40V FETs (choose high Rdson, low Qg FETs as the current is quite low). Actually, note that we also have integrated FET converters for 1A outputs.

    Regards,
    Tim