A Two-Phase Three-Level Buck Converter With Cross-Connected Flying Capacitors for Inductor Current Balancing

The two-phase operation of a dc–dc converter has several benefits, when compared with the single phase, including higher efficiency, smaller ripple, faster response, etc. However, it suffers from unbalanced currents between the two phases. This article presents a two-phase three-level buck converter with cross-connected flying capacitors (X-C
_FLY
). The proposed converter suppresses the unbalanced inductor currents in a two-phase operation, through the alternate connection of flying capacitors across the branches. Meanwhile, two-phase and three-level techniques help to achieve a fast transient response and a small output ripple. In addition, we derive the transfer function of the proposed generalized multiphase three-level buck converter with interconnected C
_FLY
for analysis, and design accordingly its power stage and feedback loop. Finally, we validate the proposed converter through the fabrication in a 65 nm CMOS GP process. It achieves a low unbalanced current close to 5 mA and a small output ripple of 50 mV for a load current around 110 mA, and a peak efficiency of about 86%.