Voltage Spikes in Integrated CMOS Buck DC-DC Converters: Analysis for Resonant and Hard Switching Topologies

In an integrated DC-DC converter, voltage spikes are generated during the commutation of the power switches and they may cause the device malfunction if its magnitude is excessive. That occurs when, targeting high efficiency, very fast switching is implemented in a low voltage CMOS process, with higher impact when the converter output current is high. These conditions that cause spikes of significant magnitude, in the order of Volts, are common in modern DC-DC converters for portable equipment powered by batteries. Magnitude limitation of voltage spikes in hard switching converters is a hot research topic and the known solutions are surveyed here. Resonant switches topologies are frequently mentioned as an alternative to overcome voltage spikes in a DC-DC converter, but generally this solution is dismissed in integrated implementations. This paper investigates if the resonant topologies are an effective solution to overcome voltage spikes during the switches commutation in a buck converter. Two buck DC-DC converters using resonant switches are analyzed, namely a QR-ZCS topology and a QSW- ZVS topology. The analysis proceeds in two steps that can be easily applied to other resonant converters. Results show that resonant DC-DC converters also generate voltage spikes which magnitude is sometimes higher than that generated in a hard switching converter, and is superimposed to the overvoltage occurring in the resonant phase. This is an important result since resonant, or soft switching, converters are occasionally mistakenly mentioned as free of voltage spikes.