SPICE analysis of RL and RC snubber circuits for synchronous buck DC-DC converters

Operation of a 1.3-MHz, 12-to-1.2 V, 20-A synchronous buck converter is analyzed by SPICE simulations. Special attention is given to two resonances formed by the capacitance of FETs in the off-state and the total inductance of the input decoupling network. The resonances are the main source of the broadband electromagnetic (EM) interference. Two most common circuit level methods for reducing the EM interference, an RL snubber circuit and an RC snubber circuit, are analyzed and compared in terms of their impact on the radiation characteristics, efficiency and reliability of the analyzed synchronous buck converter.