Research And Design Of PWM/PFM Buck DC-DC Converter

With the development of portable devices, the matching power systems required to be denser, higher reliability, higher efficiency and lower cost. The switching power took the place of the traditional linear regulated power gradually, for its prominent advantages such as lower power consumption and higher efficiency.A Buck DC-DC converter has been designed in this paper, and the analysis of the forward design methodology and optimizing of the circuit structure and parameters were also included. This converter contrived to power low-voltage digital core in mobile applications. It could provide the current up to 500mA and a steady voltage equal to 1V with the ripples less than 10mV, when the input voltage ranged from 2.7V to 5.5V.This Buck DC-DC converter consisted of an error amplifier, which has PID feedback network, and a LDO regulator, and control logic core, and the over current protection and temperature protection. The logic had two control mechanisms, the one was PWM pulse skipping feature included and the other was PFM. Also, the customers were allowed to choose the auto PWM/PFM or force PWM state with the logic control core circuit.This design of this DC-DC buck converter was based on ST's BCD6S process. And, the Cadence's Virtuoso tools were used to simulate the circuit. Last, the system simulation results showed that the circuit could supply the output current as high as 500mA with the steady output voltage 1V and the ripples were less than 10mV.