Constant ON-time 3-level buck converter for low power applications

Car black boxes operate mostly in sleep mode, which requires high efficiency for light load. We propose two schemes to improve light load efficiency of the 3-level buck converter proposed by Reusch. The first scheme is to adopt constant ON-time control with DCM for light load. The second scheme is to shut down the gate drivers for the two bottom MOSFETs allowing Schottky diodes in parallel to conduct the inductor current, in the very light load condition. The proposed converter is prototyped using off-the-shelf components. The efficiency of the proposed 3-level buck converter ranges from 82% to 95% at 100 mW and 5 W, respectively.