A ripple control buck regulator with fixed output frequency

This paper presents a ripple control buck regulator for stepping down high-voltage adaptor or battery supplies to low-voltage CPU core supply in notebook computers. Methods and circuits are proposed to achieve fixed switching frequency operation. The control loop adjusts delay of the controller and thus controls the output frequency. This is done by using a phase-frequency detector (PFD) to lock the frequency of switching signal with the input clock. The delay value is determined automatically according to operating conditions. Simulation results showed fast load and line transient responses and fixed frequency operations in steady states. In addition, stability of the regulator is shown under a very low output-to-input voltage ratio condition that is difficult for conventional PWM controllers.