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Problem with suggested MosFet

Pantelis Potiriadis
Prodigy 30 points
Other Parts Discussed in Thread: LM3478

Hi!,

I designed (through Webench, let's call it the "device". LOL.) a boost converter using LM3478. I used the suggested mosfet, NXP PSMN8R5 and i have a problem.

When i switch the power on to the device, the circuit appears to be shorted for about 2-3 seconds and then all it's ok. The step-up regulates to the desired voltage and everything seem to be ok. 

If i change mosfet with CSD18537 the problem is not appearing at all, but with CSD18563 this problem is there again.

I finally manage to work it properly with STS5NF06L mosfet of st micro, but i don't know why it's working and why not.

So I ask if you could help me make the "device" work properly.

Thank you!

  • 0
    TI__Intellectual 2930 points

    Hi,

    Can you give some more details about what you see when the circuit appears to be shorted. Is the short across the switch? Can you check the gate drive on the switch and see what it its doing during that time?

    Any waveforms and more detail you have will help diagnose the problem. Also if you have a schematic you can share, or the WEBENCH design report, that would be helpful.

    Best regards,

    Tommy