CMOS Constant-Current Driving IC For Power White LED

In recent years, solid semiconductor lighting LED (light emitting diode) is widely used due to the advantages of high efficiency, low power cost, less pollution problem, long lifetime, high reliability, etc. With the development of new material and the improvement of manufacturing process, high-power high-brightness white LED for lighting develops rapidly, which shows a tendency to replace incandescent lamp and fluorescent lamp to be a new lighting source in the field of general lighting. Therefore, the research and development on high-power LED driver IC will be a good lift on this competitive business.In this paper, a monolithic constant-current driving integrated circuit (IC) for 3W white LED with two separate output channels is proposed. It aims at driving two power whites LEDs with constant current of 350mA respectively despite of the changes in voltage supply or ambient temperature.This integrated circuit consists of bandgap voltage reference, sample-feedback control circuits and output-stage power NMOSFET, and the output power NOMSFET is the most important part of the whole chip. Therefore, the design of the power NMOSFET based on the appointed process is studied specially in this paper. The bent-gate MOSFET structure is adopted to reduce the layout area of the MOSFET, while the extended drain MOSFET structure is introduced to raise the breakdown voltage. Six MOSFETs of different structure are designed and fabricated for testing, and the optimum one has been used in the whole chip successfully, which makes it possible to compatibly integrate power device with conventional CMOS signal processing circuits.The chip is fabricated in CSMC 0.6μm double poly double metal standard CMOS process and occupies an area of 2mm×2mm. When 5V single voltage power supply changes by 10% or ambient temperature varies from 10℃to 90℃, the variance of the driving current can be controlled within 1.4% and 1.75%, while the currents of the two paths are mismatched within 2.8% and 2.5% respectively.The driving IC is used in the field of general lighting and portable equipment. The design could be improved to achieve a higher power efficiency and power-driven, with the performance to be more perfect. And compared with similar products, the chip would be more competitive.