Design and analysis for noise suppression of DC/DC converter

DC/DC converters are widely used to provide various power supply voltages required for many electronic components on a board. Though DC/DC converter is more efficient than the linear regulator is, however, the switching noise becomes larger with the increase of the switching frequency. In particular, ringing noises at the sharp rising edge of the switching waveform occurs by the effect of the parasitic inductance of trace pattern. Then, this noise spreads out to the whole circuit board, and generates electromagnetic interference (EMI), which often causes a malfunction of the other electronic systems. In this paper, the methods to accurately reproduce the switching waveforms and to reduce ringing noises were investigated. For this purpose, two evaluation boards were designed, and total equivalent model was constructed by taking into account the parasitic inductances of traces on a board. Then, frequency-domain analysis was executed to find anti-resonance peaks in impedance properties for the switching loop. Next, time-domain simulation was executed by considering parasitic inductances. Finally, the optimal condition to suppress the ringing noise and electromagnetic radiation was confirmed by adjusting the switching loop into the critical damping condition.