| With the rapid development of the electronic industry, more and more electronic devices have been emerging into people’s life and work, all of which require power to function properly. At first only a few simple electronic devices are powered, but the technical requirements of power supply are increasing with the electronic devices being sophisticated and compact, thus promoting the power of technology to higher requests and more features. A variety of power supply technologies have emerged, including the switching power supply technology. Although the rise of switching power supply technology is late, its birth has changed the face of the world greatly. Many technology- leading organizations and countries have invested a lot of effort to promote the development of the switching power supply. Since the 1990 s, the switching power supply has developed rapidly in various occasions. Notebook computers, mobile phones and cameras and other portable appliances are powered with switching power supply technology, and it is important to ensure the outside working time of these appliances. On the condition that the size and capacity of battery are fixed, how to improve the power conversion efficiency of power supply becomes a problem to be solved for technician.This paper firstly introduces the related concepts of switching power supply which includes its basics and developments, and mainly discusses the theory of buck topology, then designs each module within the chip, including the main modules and the protection modules, and some theoretical basis for the modules and the simulation results are given, followed by the analysis and the compensation of the loop stability of the system, finally the external circuit components are selected and the whole system simulation results of the regulator are given.XD1408 uses peak current mode architecture, whose purposes are to improve the sensitivity of the circuit and the speed of the circuit response, this mode can limit the inductor current in each cycle, so it has the function of over current protection; Soft Start module is embedded inside XD1408, which is different from other traditional design methods. This method uses resistance to replace the large charging capacitance, adopts digital logic, improves the module output voltage step by step, and provides a certain amount of surplus. It can restrain large inrush current effectively which may occur when the converter starts up; in the event of output voltage short circuit, the chip will automatically reduce the main frequency to 100 k Hz, so that the fall time of inductor current can be long enough to prevent runaway situation;when this chip turns off the current will drop to 1μA or less; in addition, perfect function blocks such as over voltage protection, over current protection and over temperature protection have been integrated in the chip to ensure it work stably and reliably. The technique of synchronous rectification is adopted in XD1408, without the schottky diode. This technique not only saves the cost, but also improves the conversion efficiency; XD1408 has a wide input voltage which ranges from 2.5 V to 5.5 V; its main frequency is 1.5 MHz. The higher the frequency used, the smaller the inductance and the output ripple; a kind of intermittent work mode is designed to reduce the standby power consumption, which is to say the chip uses PWM mode when it works in heavy-load; the system will automatically switch to the intermittent pattern when the load drops to light, which can also be called Burst Mode, so that the chip will possess a high efficiency.Based on a process of 0.5μ m CMOS model, XD1408 is designed with Cadence and simula ted by Hspice. The simulation results of whole system show that XD1408 can meet the standard requirements. |
PDF Full Text Request