Method to Suppress the Parasitic Resonance Using Parallel Resistor and Inductor Combination To Reduce Broadband Noise from DC/DC Converter

Synchronous buck converters generate broadband noise typically in 50 – 300 MHz range due to the parasitic LC resonance in the switching loop which consists of input decoupling capacitors, high-side MOSFET and low-side MOSFET. Typically, this parasitic resonance is attenuated using an R-C snubber placed parallel to the low-side MOSFET. However, selection of the R and C value of the snubber is not a trivial task. This paper presents a new type of snubber structure utilizing a parallel combination of a resistor and an inductor in series to the switching loop. Different possible implementation strategies include using discrete resistor and inductor and using PCB trace as an inductor. The experimental result shows that the R-L snubber can result a significant reduction in phase voltage ringing as well as the radiated broadband noise.