A Monolithic Buck Converter With Near-Optimum Reference Tracking Response Using Adaptive-Output-Feedback

A monolithic output-ripple-based buck converter with adaptive output and ultra-fast reference tracking is presented. Fixed-switching-frequency V²-control is used in steady-state operation; while its speed limitation during reference tracking is eliminated by employing end-point prediction, a novel oscillator with clock-holding function, and the proposed adaptive-output-feedback (AOFB)-scheme. The AOFB-scheme is obtained from a detailed analysis of the dynamics of general output-ripple-based controller during reference tracking. Then, an adaptive feedback voltage which satisfies the switching criterion for optimum switch control in reference tracking is formulated, and is incorporated into the controller design. The resultant single ON/OFF-switching during reference tracking is very close to the optimal solution for fast reference tracking. Moreover, it also leads to the lowest switching loss and minimized conduction loss at the fastest tracking speed, making the converter very suitable for adaptive-output applications. Fabricated in a 0.35 mum CMOS process, the 3-V input prototype chip exhibits stable operation across a wide output range of 0.7-2.4 V. High tracking speed within 10 mus/V is measured with different output voltages and output voltage steps. Maximum efficiency of 96% is obtained at 260 mA output current, while maximum output current is 800 mA.