LM5118-Q1: Switching Wave form exceeding mosfet and diode maximum limits.

Shashank Hoysala

Part Number: LM5118-Q1

Hi team,

I have design a DC-DC converter using LM5118-Q1 IC with Specs Input range =12V-36V and output = 24V 3A. the output is coming fine line regulation, load regulation and efficiency is also good.

but the MOSFET and Diode waveform are seems unsatisfactory peaks of some 10 - 20nS is going above the rated voltage of MOSFET and Diode. will it create any issues please suggest.

I am attaching the Schematic PDF and Test report with waveforms.

24V 3A DC.docx

over 1 year ago

0 Feng Ji over 1 year ago

TI__Genius 13955 points

Hi Shashank,

Please make sure you are using tip and barrel method for the measurement.

With the tip and barrel method, if the peaks is still higher than the rated voltage in steady state, I think it is not acceptable.

Best Regards,

Feng Ji

0 Shashank Hoysala over 1 year ago in reply to Feng Ji

Prodigy 20 points

Hi Feng,

Thanks for your suggestion. I tried with barrel now the Peak voltage across the mosfet is under 45V which is 80% of its Max VDS. but the Diode D3(Buck diode) spike is crossing above 60V whose VBR is 50V only. can you please suggest me any solution to reduce that spike. can I use RC snubber across the diode to reduce it.

0 Feng Ji over 1 year ago in reply to Shashank Hoysala

TI__Genius 13955 points

Hi Shashank,

You may improve the voltage spike by:

Improving Layout
Increase gate resistor of the MOS
Add RC snubber

Best Regards,

Feng Ji

0 Shashank Hoysala over 1 year ago in reply to Feng Ji

Prodigy 20 points

Thanks Feng Ji,

I will try your suggestions.

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LM5118-Q1: Switching Wave form exceeding mosfet and diode maximum limits.