Research And Design Of A High Efficiency PWM/PFM Buck Switching Power Supply

Portable electronic devices, such as smart phones, PAD, and laptops, has been becoming more and more popular in our life, and the performance of electronic product become increasingly demanding. Buck DC-DC converter, as a fundamental part of the power management unit, has been facing the challenge of providing larger power density,small size and high efficiency.The graduation project is proposed a step-down DC-to-DC converter which based on a PWM / PFM modulation and as a power management chip is suitable for portable electronic devices.Firstly, according to the research status of step-down switching power supply and the development trend of power management chip. Taking into consideration the aspects of improving conversion efficiency, reduce chip area, the ripple voltage, then given chip design specifications and best design. With supply voltage ranging from 2.7V to 5V,output current up to 500 mA. The chip is integrated with over temperature protection and under voltage lockout. To improve the efficiency, the converters operates in a synchronous mode, pulse width modulation(PWM) and pulse frequency modulation(PFM) combined control mode. To reduce the chip area, the power tube, rectifier and compensation network are integrated in the chip, only a 2.2?F supply voltage filter capacitor, a 1?H output inductor, a 4.7?F output capacitor, these devices are small patch devices, namely to achieve a high power density.Secondly, according to the system design, the design includes a reference voltage source, an oscillator, an error amplifier, soft start circuit, a current sampling circuit, and protection circuits. These circuit modules have been carried out principle analysis and performance simulation.Finally, the proposed converter is designed with SMIC0.18?mCMOS process, and simulated in Cadence. The simulation demonstrates that the chip is able to work steadily at 1.2MHz switching frequency, generating a 1.5V output voltage with the ripple less than1%. The mode switch can be achieved, furthermore, the efficiency remains higher than85% in wide load range, the efficiency peaks at 95% when the output current is at 100 mA,which meets the target specifications.