Design Of Current Mode White LED Driver

With the fast increase in portable electionics powered by all sorts of batteries, the demand for the power management ICs, especially the highly efficient switch-mode DC-DC converter, will get bigger and bigger.Traditional types of power supply chips such as low Drop-out and Charge pump, have limited efficiency and output range. DC-DC converters are used widely because of its high efficiency and miniaturization. Academic research in DC-DC converter will make a big contribution to China's power management industry.In this paper, we use current control mode, which can achieve better voltage regulation ratio and load regulation ratio, in the mean while system stability and dynamic characteristics are improved significantly and there is no magnetic bias, besides, it is easy to sense peak inductor current. However, as an current feedback loop is added in the design, the whole system stability is highly affected, for instance, there are problems such as the output peak inductor current being constant while the average current being not constant, and disturbance response of the inductor current. They are the pinch points in the design of current mode as well as the emphasis of the research.In this paper, we have designed a boost white light LED driver chip which is used for back light, and we have finished the design of the modules such as oscillator, band-gap, current reference,OTA, over-temperature, over-current and over voltage protection. An error amplifier and a compensator are designed to improve the stability of feedback loop, dynamic behavior and load ability, according to the characteristic of continuous current mode. The chip is taped-out in CSMC 0.5μm CMOS process and the software of cadence is used in simulation and verification. It operates at the frequency of 1 MHz with the output current from 15mA to 60mA and the output voltage up to 20V, and it can drive two to six White LED series. The peak value of conversion efficiency is 88%.