Design Of Series-type White LED Dirver IC Based On PWM Control Method

The market of power management IC grows rapidly in worldwide,especially in Chinese Market.And the driver of the white LEDs for display-backlighting has become one of the fastest growing power management IC chips.With the higher and higher luminous efficiency and decreasing cost,the white LEDs have been used in many aspects,including display backlighting,power lighting,and so on.The white LEDs have been widely used for display backlighting of mobile phones,MP4,and other portable products.High light uniformity and brightness is needed for display backlighting,as well as the white LEDs have some disadvantages,so that needs excellent white LEDs driver IC chips.This paper designed a DC-DC boost chip with PWM controlling mode that can be widely used for display backlighting of many portable products.The chip used the dual-loop feedback controlling mode and peak current detecting methods,in the range of 3~6 volts fo input voltage,the constant output current is 20mA,can steadily drive a group of 3 white LEDs in series,in extreme can drive 3 groups.The chip has a high-power switch MOS,an oscillator of 750kHZ frequency,a PWM comparator,a band-gap voltage reference,and so on.The chip has been designed by the standard of CSMC 0.5um two-polysilicon,triple-metal CMOS process.This paper introduced the application of the white LEDs,the latest development of the white LEDs driver,and then described the basic structures,the working principles,the advantages of the PWM controlling mode,and proposed the targets of this chip.According to the targets,designed the overall structure of the chip,and divided it into several sub-modules.Make use of Cadence to complete the design and simulation about each sub-module,focused on analyzing the band-gap voltage reference,oscillator and slope compensation module.On these bases,selected the appropriate external device models,the chip had made the overall simulation of voltage and transient performance,to ensure good performance under the different process corners,under different input voltages and different temperatures,and did some amendments based on the lack of submodule.The results showed:under typical application conditions,its start-up time was less than 200μs,when the voltage occurs jumped,the chip could rapidly stabilized output,the output current was constant ,and its variation was below 2%,the power conversion efficiency was above 68% within 20~60mA driving current.Finally,depended on Cadence's Virtuoso Layout Editor design tools and Assura layout verification tool to complete layout design,DRC,LVS verification and post-simulation.