A 10/30MHz PWM buck converter with an accuracy-improved ramp generator

In this paper, a 10/30MHz PWM buck converter with an accuracy-improved ramp generator is proposed. To extend the minimum duty ratio of the converter, the valley of the ramp signal is controlled to be larger than 0.2V by the threshold voltage of an NMOS transistor. To shorten the delay time of the comparator in the ramp generator, a high speed two-stage push-pull comparator is presented. Simulation results of the ramp generator with switching frequencies from 10MHz to 30MHz show that the error due to process variations for the ramp, clock and maximum duty ratio are not larger than 10%. To avoid the design of high speed current sensor and maximize the unity-gain frequency of the regulation loop, voltage mode control with type III compensation is adopted for the converter. Measurement results show that the proposed buck converter with 500mA of load range has good steady-state and transient performances for 10MHz and 30MHz of switching frequencies, respectively.