App note: Snubber design for noise reduction in switching circuits

Minimize noise by properly designing a snubber circuit in switching converters, app note from Alpha & Omega Semiconductor. Link here (PDF)

In high frequency switching converters the designers face a common challenge of dealing with switching noise. In particular when the high side Mosfet turns on, the body diode of the low side FET, which was in conduction before, turns off. During the turn off process the body diode draws a peak reverse recovery current and then abruptly snaps off. Since there is a small but finite parasitic inductance in the circuit, the reverse recovery current will circulate through the circuit until it dies down. This will result in voltage overshoot and ringing at the phase node which is quite undesirable. If the overshoot is severe enough, the low side FET may turn on again or go into avalanche breakdown. On the other hand the ringing may cause negative spikes with respect to ground, and these spikes may get coupled to the sensitive electronic components in the load causing malfunctions.

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