LM3150: switching frequency missing pulses

Jon Hurwitz

Part Number: LM3150

Tool/software:

I designed a 5V buck based on the LM3150 to support a 4A load.

On the LM3150 EVM I have, the switching frequency of the high gate is stable under load or no load. On my own design (wide input 5V buck), the frequency seems to skip a pulse when there is no load:

When there is any load applied, the switching frequency seems to have a lot of jitter, and also skips pulses:

Here's a screenshot of my design. Note that I made a mistake tying the EN to the input voltage, so I just cut the pin on the IC to prevent it from being connected, it is floating.

over 1 year ago

0 Frank De Stasi over 1 year ago

TI__Guru 72415 points

Hello

Since this is a COT controller, you will need to be somewhat careful about your feed-forward capacitor and your output capacitor ESR.

Please check the quick start calculator on the product page for this device and compare with your design.

Or, you can use Webench to check your component selection.

Thanks

0 Jon Hurwitz over 1 year ago in reply to Frank De Stasi

Prodigy 45 points

I just tried to use the quick start calculator but there are a ton of excel errors for some reason. So I threw my requirements into webench and it suggests 100pF Cff at 74mOhm (C0805C101K5GACTU) and 150uF Cout at 25mOhm (6TPE150MAPB). The 2x 150uF caps I have on there right now are each 17mOhm ESR.

0 Frank De Stasi over 1 year ago in reply to Jon Hurwitz

TI__Guru 72415 points

Hello

Try removing one of your 150uF output caps.

Also, you could try to build your application on an EVM and see what response you get.

Thanks

0 Frank De Stasi 11 months ago in reply to Frank De Stasi

TI__Guru 72415 points

Hello

I will close this post due to inactivity.

If you need further help, please open a new post.

Thanks

Power management

Power management forum

LM3150: switching frequency missing pulses