A Low Ripple Frequency-Feedback PFM-PWM Buck Converter with Seamless Mode Transition

A low ripple frequency feedback Buck converter is proposed. And a frequency feedback loop control method instead of hysteresis comparator is adopted in the Buck converter to implement PFM modulation, which eliminates the output ripple limitation caused by hysteresis comparator's hysteresis limit. In addition, the PFM mode of frequency feedback is modeled, and it is analyzed that a type II compensation can ensure stability of the PFM mode. Furthermore, an analog control method is also utilized for smooth switching between PWM and PFM modes. The simulations result shows that proposed Buck converter achieves an output ripple of only 4mV under a 0.1mA load.