Constant-on-time-Controlled Buck Converter using Switching Period Estimator

This paper presents a novel control method for constant on-time (COT) buck converters. The converter employs a high-accuracy switching period estimator in conjunction with a constant on-time generator to stabilize the system, eliminating the need for inductor current sensing or particular ripple injection. The proposed switching period estimator can adaptively adjust the switching frequency according to the load conditions, enabling high-speed output voltage regulation. Since there is no need to sense current nor any offset compensation, system complexity is reduced and efficiency is improved. A 3.3V input, 1.8V output buck converter designed using the proposed control method has been validated for various output current capabilities. The performance shows a maximum output voltage ripple of 20 mV, and recovery fall and rise times of 3.9 μsec and 4.8 μsec, respectively, under a 500 mA load change. The peak efficiency is >95% and the maximum undershoot and overshoot voltages are 49 mV and 57 mV, respectively.