Research And Design Of A BOOST DC-DC Converter XD2939for White LED Driving

The BOOST DC-DC convertor XD2939is designed for driving white LED. Thisconvertor can be widely used in portable electronic instruments such as mobile phones,MP3, digital cameras, and so on.The paper firstly introduces the development and wide use of white LED(lightemitting diode), and concentrates on the theory of SMPS(switch mode power supply),in terms of the popular operation modes and control methods of BOOST DC-DCconvertor, and the drive principle of XD2939is then confirmed. Then the system designof XD2939and electrical characteristics are introduced, and the critical designtechnique of XD2939including PWM(pulse width modulation) control mode and loopcompensation are also presented. Some typical sub-blocks are emphatically analyzed,such as the voltage reference block, OSC(oscillator) block, soft-start block, currentsense block，error amplifier and over temperature shut-down block. Finally, thesimulation results of the whole chip are given.XD2939works at the frequency of1MHz, saving the PCB(printed circuit board)space because of the small components. The peak current pulse width modulation ischosen for the loop control of XD2939, making the chip’s transient response to thesupply voltage and the load current faster. The inner loop compensation and soft startcircuits provide an easy choice for the outer capacitor, and what’s more, the innerintegrated circuits such as over current protection, over voltage protection, thermalshutdown and under voltage lockout make the operation of the chip more secure andstable.The design and simulation of XD2939are completed by using Hspice softwarebased on the0.4μm BCD(Bipolar-CMOS-DMOS) process. The simulation results showthat the performance is excellent and can satisfy the prospective demand.