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WEBENCH® Tools/LM5176: Large oscillations in in a buck leg.

Andrey Yakimov
Prodigy 190 points
Part Number: LM5176
Other Parts Discussed in Thread: CSD18532Q5B, CSD17573Q5B

Tool/software: WEBENCH® Design Tools

Hi Team,

I'm developing lead battery and supercapacitor charging device based on LM5176.

9-15V VIN   …..  0-15V 9A OUT CCM - mode; DITHERING - disable; NO BIAS supply; Frequency 250 KHz.

I used IPD031N06L3GATMA1 MOSFETS in a buck and bust leg. Ciss 10 000 pF;  Qg 59 nC.

Now I install the new one in a buck leg CSD18532Q5B.  Ciss 3 900 pF;  Qg 44 nC. to reduce the capacity load to lm5176.

In a bost leg I install CSD17573Q5B.

I see large oscillations in in a buck leg after the replacement.

What can be the problem? I'm afraid, that Uds max.=30V may be overload.

Thanks!

  • 0
    TI__Mastermind 21720 points

    Hi Andrey,

    It is important to probe the SW voltage properly having as short as ground lead as possible. This will give a more accurate reading of the peak voltage.

    When changing MOSFETs this ringing frequency and peak is going to change due to a number of parameters. One of the best ways to work around this is to add a snubber and tune it to make sure the ringing on the switch node does not exceed the MOSFET voltage. Here is an application note that covers how to tune a snubber properly.

    -Garrett