Abstract: A 750mA output current,high stability,high efficiency step-down DC-DC converter with pulse-width modulation and pulse-frequency modulation modes is presented.Under nominal load current (＞80mA),the converter operates in PWM mode with a fixed switching frequency of 1MHz.At light load current (＜80mA),the converter enters PFM mode operation with reduced switching frequency and less quiescent current.Therefore,the converter achieves the highest efficiency over the entire load current range from 0.02 to 750mA.Moreover,an advanced fast response voltage mode control scheme achieves superior line and load regulation.The chip was implemented using a CSMC 0.5μm CMOS 2P3M mix-signal process.Simulation results indicate that the converter can automatically switch between PWM-mode and PFM-mode according to the load current.The maximum conversion efficiency is up to 96.5% and it is more than 55% at 0.02mA of load current.The proposed chip is especially suitable for portable systems powered by batteries.

Key words: DC/DC converter, step-down converter, PWM, PFM, high efficiency