A Novel Seamless PFM/PWM Mode Switching Circuit in Peak Current Mode Controlled Buck Converters

This paper presents a seamless transition circuit for PWM/PFM in a peak-current-mode-controlled buck converter. By adding clamp circuitry and a circuit module for frequency reduction based on clamp current to the existing PWM loop control, PFM is achieved without the need for an additional control circuit ,which reduces circuit complexity while enhancs detection and control accuracy. The frequency reduction generated by the PFM controller automatically adjusts according to changes in feedback voltage, thereby improving the system's dynamic response characteristics. Additionally, during operation in PFM mode, the PWM control module is deactivated, reducing system losses. The proposed seamless transition circuit is applied to a peak-current-mode-controlled buck converter and simulated in 0.18um CMOS process. The simulation results indicate that the system achieves a smooth transition between PWM and PFM modes. During the switching process, the transient variation in output voltage is less than 42mV, demonstrating favorable dynamic response characteristics. The buck converter using the seamless PWM/PFM transition control achieves 97.1% peak efficiency.