A Design Of Hysteretic Constant Current Mode LED Driver IC

The exploitation and utilization of energy sources has gradually become a major issue related to the livelihood of human beings, governments around the world have proposed energy conservation as a basic national policy. The LED industry, represents a series of energy-efficient-oriented business, is leading a reform of cross-age sense. As the key link of the LED industry’s chain, the LED driver IC is bound to have a broad development space.In this paper, switching power supply technology, analog integrated circuits principle and high-voltage BCD process technology are used to design a hysteretic mode constant current LED driver IC. The main problems are reflected in improving the constant current accuracy, reducing the power consumption, controlling the operating frequency, reducing the process variation and other aspects.As response to these problems, this paper, based on the understanding of the controlling modes of switching power and the schemes of the signal sampling, has made an analysis of the principle and the feasibility of the hysteretic control mode. The internal performance of the chip is carefully studied and a scheme meets the indicators is designed. The main contents of this paper including the following aspects:1. Study on the development of LED, analysis of the market and tend of the LED driver IC. Combined with the characteristics of the LED, the constant current driver scheme must be used. The difference between linear constant current scheme and switch mode constant current scheme are further analysis. Then the control modes of switching power, the scheme of the signal sampling are studied in detail and the advantages and disadvantages of these programs are pointed out. At last, a hysteresis mode constant current IC is proposed.2. Design the block of the IC, define each parameter. Design reasonable structures and parameters for each sub-module. Verify the properties of the sub-modules by using Cadence Spectre simulation tools. Sub-modules mentioned in the paper including power reference, hysteresis comparator, timer, etc. In this paper, specific circuits of the sub-modules are designed and the impact of process variation is minimized. At last the indicators of the IC are verified through the whole simulation. The input voltage range of the IC is 9~40V, the output current is 250 mA, current precision is ±5%.3. Propose IC layout design based on the 1μm700V high-voltage BCD process. Reduce parasitic parameters of process and temperature distribution that affects the performance of the IC by reasonable layouts and routing methods. Finish the overall layout design, while design the layout for testing the important sub-modules.