Design Of A High Efficiency Charge Pump DC_DC White LED Driver

Power management IC becomes more and more important due to popularizatization of portable equipments. High efficiency, low cost and low noise are becoming the development trend of DCDC regulations. White LED driver has been chief market for power manager IC these years. And charge pump converters become more attractive, because the tructure of charge pump can perform the conversion of rising input voltage without use of inductor.By using a 0.5μm CMOS process, a high efficiency charge pump DCDC white LED driver is designed in this paper, which based on an auto-adjust capacitor charge pump. It produces a regulated output voltage 5v from a 2.7v to 5.5v input with up to 100mA of output current. Its shutdown supply current is lower than 1μA when chip is in the shutdown mode. The switching frequency is 1MHz. High switching frequency enables the use of small ceramic capacitors, so it can reduce disturbtion of EMI and the cost. Its operating temperature is -40°C to 85°C. The chip implements a thermal shutdown mechanism to protect the device from damage due to overheating and an under voltage lock out mechanism when the input voltage is too low. A tightly controlled soft start feature limits inrush currents during the chip activation.Frist, the system design and its block diagram is introduced. 1.5x/2x auto-adjust charge pump is design according to the principle and structure of charge pump, which can automatically convert working mode with the change of input voltage. Then, important parameter of charge pump is analyzed in details. The sub-circuits are discussing, including of bias, band gap, oscillator, logic control, error amplifier a, over thermal protect, etc.Based on the principle analysis and circuit design, the system and its sub-circuits are simulated by EDA tools HSPICE, the simulation results reach the requests and verified the correctnesss of the principle analysis and circuit design. Some layouts of sub-circuits are designed at last.