| LED has been widely used in the LCD backlighting, cell phone camera’s flashlamp, automotive lighting, traffic lights, home lighting and other fields. With thedevelopment of science and technology as well as the increasing demand for LED,Designers are increasingly pursuit for high performance LED driver, high precision,high conversion efficiency, wide input range and other characteristics becomeimportant parameters to measure the performance of a product. In order toguarantee consistency of the emission intensity of each LED, a control chip whichcan provide a stable current is particularly important.This paper briefly introduces the basic concept of LED, and focuses on the workingprinciple of the PLM. Then a high precision, high efficiency and high power LEDdriver is designed by using this technology. PLM is a novel method of controlling,compared with the conventional peak current control method, the PLM methodreally achieves the control of the LED’s average current, more efficient and moreaccurate. In addition, the low-side sampling structure helps simplify the samplinglines and improve the conversion efficiency.According to the above requirements, the overall framework of the chip and thecircuit modules include input voltage regulator, oscillator,1.2V reference generator,bias current generator, over-temperature protection, over-voltage protection,under-voltage protection, PWM comparator and ESD protection are designed next.At last, all modules’ simulation results are given especially the performancesimulation of the whole circuit. This design is based on CSMC40V/VDS/0.5μmBCD process and use Spectre emulator of the Cadence platform to finish the circuitdesign of the driver chips. The input voltage of this chip is from6V to40V, and theconventional output current range is350mA to1000mA. The chip can drive up to11whiteLED, and the highest conversion efficiency is about96.5%. The chip’s layout isdesigned by using Virtuoso layout tools, finally the chip is fabricated and tested. |
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