Variable On Time Controled Buck Converter For Dvs Applications

Variable on Time (VOT) control is proposed in the paper. Compared to conventional constant on time (COT) control, the on time of VOT control is modulated by output of error amplifier, rather than fixed voltage. VOT controlled buck converter shows significant duty cycle extension than COT control, especially for high switching frequency and wide input/output range applications, such as DVS converters The duty cycle limitation of COT control is then broken through. The small signal model derivation based on Describing Function (DF) is given. A 1MHz 12V-1.2V buck converter with VOT control is designed with 0.35 m BCD process. Simulation results show that the recovery time is 5 mu s for 4A load step, and the undershoot voltage is decreased from 50mV to 35mV, by using VOT controL The voltage scaling speed is 20 mu s/V for 47 mu F output capacitor. The reference up-tracking shows FOM of 0.42s/(F.V), which is much better than previous works.