Buck switching regulator with improved mode transition and control method thereof

A method for controlling a buck switching regulator, comprising the steps of:

• providing a switching regulator including an output power stage for converting an input voltage to an output voltage, the output power stage being controlled by a first PWM signal during a FPWM mode and being controlled by a first voltage signal during a PSK mode, wherein the first PWM signal is generated according to the first voltage signal;
• and
• in a transition from the PSK mode to the FPWM mode, providing a second voltage signal as a starting point for the first voltage signal, the second voltage signal being substantially close to a target of the first voltage signal in the FPWM mode, wherein the step for providing the second voltage signal includes:
• receiving a second PWM signal and converting the second PWM signal to an average voltage output;
• comparing the feedback signal relating to the average voltage with a reference signal to generate the second voltage signal;
• and
• comparing the second voltage signal with a ramp signal to generate the second PWM signal.