Low Input Dc/dc Converter In The Research And Design

With the development of the integrated circuit industry, the requirements of the electronic equipments for the switching power supply have gradually improved, including highly integration, low power, high reliability and high convert efficiency and so on. Therefore, it is obviously necessary to study the switching power supply. In this paper, after in-depth studying and researching the basic principles of DC/DC converter, a new type of step-up switching power supply chip was designed. This chip have a lot of different characteristics such as wide input supply voltage range, high convert efficiency and simple external circuits.etc. With the input voltage between0.8V-4.5V, the converter can provide up to500mA load output,5V output voltage. The output ripple voltage is less than1%. And the convert efficient is up to90.9%.A DC/DC converter system was designed at the basis of deeply analyzing the fundamental principles of DC/DC converter control mode and considering the advantages and disadvantages of the PWM control mode and PFM control mode. The converter system used a peek current and fixed frequency mode PWM control scheme.The synchronous rectification method was applied to improve the conversion efficiency of the boost converter system. The open-loop stability problem caused by peak current control mode of the converter system was proposed in the paper. And the slope compensation was added in this system in order to eliminate the harm caused by the sub-harmonic oscillation. Because the system can not start up at low supply voltage, so a new solution was proposed. The power converter system was started up partly, and the output voltage was raised step by step, then the system worked steadily. The converter system framework was proposed after the above theoretical knowledge was analyzed. The value of the output capacitor and the energy storage inductor should be resized in order to achieve the perfect results although the value has been calculated theoretically.This converter system was designed based on bottom-up design methodology. The principles were understood firstly. Then the submodule circuits were designed and were made simulation using Spectre simulator. The simulation includes timing simulation, DC simulation and frequency domain simulation. Debug the circuits to meet the functional requirements and performance index. The specific modules include current source, band-gap reference, ring oscillator, window oscillator, comparator, error amplifier, LDO, slope compensation circuit, level shift circuit and driver circuit, and so on. Finally the system simulation was done in order to verify the design feasibility and make sure that the plan is right.The design was finished based on the NEC0.35um technologies, Cadence design software and Spectre simulation software. The simulation results show that the converter designed meets the design requirements.