The Research And Design Of Buck DC-DC Converter

In recent years,more and more electronic devices flow into the market, especially portable products,such as mobile phone,PDA,digital cameras and so on. Power supply is the power supply system of electronic equipments.The quality of power supply directly determines the performance of electronic equipments.DC-DC converters are widely used in the power management of portable devices,they improve the power supply system of portable equipments and extend the working hours of battery power.The primary circuit structure and basic principle of Buck DC-DC converter are introduced firstly in this paper,and the modeling methods of DC-DC converter are briefly discussed,then the modulation modes of DC-DC converter such as pulse width modulation(PWM),pulse frequency modulation(PFM) and PWM/PFM hybrid modulation are introduced and analyzed.PWM mode has high efficiency under high load.PFM mode has high efficiency under light load.PWM/PFM hybrid modulation mode is the combination of PWM and PFM.According to the variation of the load, PWM/PFM can automatically switch so that no matter high load or light load,it can maintain a high conversion efficiency.This satisfies the needs of power management chip for portable electronic products,such as high efficiency,low power,small size, light requirements.PWM/PFM hybrid modulation mode is used in this paper.The key blocks of DC-DC converter including comparator,cascode OTA,buffer, clock and ramp signal circuit,current sensing circuit,voltage to current converter circuit, pulse width modulator,PWM/PFM selection circuit etc.are designed based on SMIC 0.18μm CMOS Mix-Signal process and simulated under Cadence Virtuoso ADE environment.Finally,the performance of Buck DC-DC converter system is simulated. The simulation results shown that the system can work properly.Its performance meets the design requirements.