Research And Design Of White LED Driver IC Based On Boost Switching Power Supply

As the best choice of small-size LCD's backlights, white LEDs have been used more and more in portable applications such as mobile phones and digital cameras. Meanwhile, white LED driver IC, which is the key component of LCD backlighting system, is facing critical challenge in its design. Because of the demand on small size for handheld devices, white LED driver IC should have the figures of high efficiency, high reliability and high power density.In this thesis, with the in-deep study of current technique for white LED drivers, three main driving methods are proposed firstly. According to the application demands for this research, one of these methods is chosen for the design, which is based on Boost DC/DC switching power supply. And then, the key interrelated technique for Boost DC/DC is studied and the whole chip structure is constructed. The main subcircuits such as bandgap reference(BGR), ramp compensation and digital interface are designed and implemented with UMC 0.6μm BCD process, and the simulation results are also presented. A novel bandgap core structure is used in the BGR. Compared with conventional bandgap reference circuit, this bandgap structure is more immune to errors caused by current offset; a dynamic ramp compensation technology is used so that the over compensation problem in Boost DC/DC can be solved; the unique digital brightness control function can save processor power and battery life.Finally, the whole chip simulation results by HSPICE are given: in typical application condition, the start-up time of the chip is only 300μs; the efficiency is above 80% when the LED current ranges from 10mA to 40mA; the digital brightness control and PWM dimming functions can be operated properly. In a whole, the results show that the main electrical characteristics of this chip matched the specification.