Electronic – Any qualitative analysis saying RC snubber required or not for High current Buck converters

buck

I have a design where i am using TPS53355 from TI to generate 0.9V @ 15A from 12V(10V-14V).
For this design, i want to know whether RC Snubber required or not?

as far as i know,

Generally in High current converters inductor will store lot of energy = (1/2)*L*i^2.

If there is a gap between upper MOSFET(Control MOSFET) Off and Lower MOSFET(Sync MOSFET) ON, whole energy stored in inductor will be collapsed suddenly, can develope large spike on LL pin of V = L* di/dt.

In our case, L=0.47uH, Imax = 15A, energy stored in inductor will be = 0.5*0.47uH*15*15 = 53uJ.

I am not sure in the case of TPS53355, whether any delay between Control MOSFET OFF to SYNC MOSFET ON and the rise and fall times of MOSFET driving circuitry.

if Control MOSFET turnOFF time is approx 50ns.

then V = 0.47uH * 15A/50nSec = 141V. then this much voltage(141-12) has to be withstand by internal MOSFET for the duration where Control MOSFET is OFF and before Sync MOSFET turns ON.
Generally Internal MOSFET's will not have higher breakdown voltages due to their space constraints. How we can be sure that internal MOSFET will not damage for this spike.

in the datasheet of TPS53355, i didn't find these details regarding timings of Turn ON and OFF,But the recommended circuits have Snubber placed in.

There is "Dead time" between Control MOSFET oFF to Sync MOSFET ON to reduce any shoot through. any details regarding this also helpful.

**One more question is,
In one of the literature,
i read that due to parasitic effects of inductor and capacitor we will have spikes at the switching node (here LL), But i thought because of sudden change in current, voltage spikes will occur at the switching node, am i correct* .*

Best Answer

Have you considered that the parasitic diode inside the lower mosfet (in a synchronous buck) will conduct and reduce the projected (-)141V you mention? There is also the parasitic capacitance of the inductor which will also tend to reduce this "spike" and convert it to a decaying sinewave until the lower mosfet turns on.

Regarding your "one more question" I think a link may be missing (here LL)?

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