Forum Post: LM3150 DCDC 12Vin - 3.3Vout 8A, oscillation in SW pin

Hi,

We have implemented a webbench design, based on LM3150.

It's a 12Vin, nominal, to 3.3Vout  8 A.

It powers a highly capacitive load (8x 680uF tantalum capacitors)

When I look at the voltage at pin SW, with almost no load (some logic plus the 680uF capactiors), we see a clean step waveform

But when we apply any load (by the moment a resitive load, plus 680uF capacitors), we can see some kind of oscillation, that we think it doesn’t be there

And zoomed

I use the webbench part numbers, excep for:

* Cin. I have two additional CAPs ( 100uF 25V electrolitic aluminium) before Cin.

* Css. I have changed Css to 1uF to slow down the ramp-up.

* Cout. I use two 680uF 6v3V in parallel befor plane conection (0.6 ESR each).

Is this oscillation undesirable?

any clue on what is causing this oscillation?

thanks

PD.- the webbench desing:

(Please visit the site to view this file)