| The developping mobile Internet technology, which based on thecommunicating and network platform,has led to the rapid development of PAD, smart phones, Bluetooth speakers, OTT box which as the representative of portable electronic products. Because of the battery technology is difficult to improve in a short time,it maybe the best chose to extended battery operating time and enhance endurance of the chips,which by the means of optimising the loop control to enhance the power efficiency.This paper mainly from the point of view of increasing the power efficiency of portable SOC chip,to research and design on the step-down switching converter.Firstly, by the means of analysis the power loss characteristics of the buck converter, we find that the important factor affecting of conversion efficiency is the loss of power on the tube. Through comparative analysis of PWM(Pulse Width Modulation) and PFM(pulse frequency modulation) characteristics of these two modes, using dual-mode control PWM and PFM during the full load range, thereby improving the conversion efficiency of the chip. In order to improve the anti-disturbance performance of the switching converter systems, respectively, single loop voltage control and current loop control characteristics were analyzed and compared, and we chose the peak current-mode pulse-width control with the current sampling pulse frequency control as the system control mode of this thesis.Secondly, according to the system architecture used in this paper, focusing on the small-signal modeling of non-ideal parameters peak current mode PWM modulation, as well as the completion of the design of the control loop frequency compensation, and raised PFM system is designed.Finally, analysis and design of the main function module circuits of the control system by using the process of CSMC 0.25 um BCD. The system simulation results show that the PWM mode has good resistance to disturbance and response speed, and the converter can automatically switch between PWM / PFM mode. Power analysis put forward that the conversion efficiency under heavy loads in more than 85%, at light load 1mA at 50% conversion efficiency, and thus achieve a full load range of high conversion efficiency; The input voltage and load current disturbances adjustment time within 20 us, and line regulation and load regulation are less than 1%,and the voltage(current) ripple rate is less than 1%. |
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