A Single-Mode Buck-Boost Converter with AlwaysDual-Path Operation for Inductor Current Reduction

This paper presents a battery-to-3.4V buck-boost converter designed for mobile devices. The converter employs two flying capacitors (CF1 and CF2), one inductor (L) and six switches. CF1 operates in parallel with the inductor to distribute input current during inductor energizing phase, while CF2 assists the inductor in transferring output current during the inductor deenergizing phase, ensuring the inductor current (IL) is always lower than the output current (IOUT). This configuration results in a single-mode controlled buck-boost converter, allowing smooth voltage conversion over the entire battery voltage range. Additionally, the maximum voltage stress on switches is limited to either VIN or VOUT, enabling the use of 5-V devices for all power switches. Furthermore, the non-stopping output current delivery alleviates the right-half-plane (RHP) zero effect, leading to fast transient responses. The converter was fabricated in a 0.18-μm BCD process. Measurement results demonstrate that the converter achieves a peak efficiency of 97.3% using a bulky inductor with a DCR of 18 mΩ. The peak efficiency remains at 96.4% using a compact inductor with a DCR of 200 mΩ.