Design of Digital Tri-mode Adaptive-Output Buck–Boost Power Converter for Power-Efficient Integrated Systems

An integrated buck-boost converter with a tri-mode digital control is presented. It employs an adaptive step-up/down voltage conversion to enable a wide range of output voltage. This is beneficial to the ever-increasing electronic systems that employ dynamic voltage scaling (DVS) techniques for power-efficient operations. Three control modes are employed in the converter to operate jointly and seamlessly for performance optimization during the periods of start-up, steady state, and dynamic voltage/load transient states. To avoid latch-up problem and minimize leakage current, an automatic substrate switching circuit (ASSC) is introduced. The design was fabricated in a 0.35-??m digital CMOS N-well process, with a die area of 1.3 mm². It precisely regulates an adaptively adjustable power output from 0.9 to 3.0 V. The maximum efficiency is 96.5%, which is measured at 0.9-V output and 45-mW load power. The efficiency remains above 50% over the entire 800-mW power range. The converter responds to a 45-mA load step transient change within 600 ns. The DVS tracking speed is 37 ??s/V for a 1-V step-down change and is 150 ??s/V for a 1-V step-up change. With a line regulation of 20.4 mV/V, the converter functions robustly when the input power source frequently varies between 1.6 and 3.3 V. The ASSC consumes only 88- ??W static power.