Based On The Logarithmic Dimming Led Drive Efficiency Charge Pump Circuit

New requirements will be needed in the power management due to the popularization of portable equipments powered from battery. In the regulations kinds, charge pump converters become more and more attractive in the low or medium power applications because of using no inductors, low external parts count, designing easily, small PCB area, high efficiency, low cost and so on.A low noise, constant frequency charge pump DC/DC converter circuit using 0.5μm CMOS technology is presented in this paper. It uses fractional (1.5X) conversion to increase efficiency and linear mode to produce lowest possible ripple. The devices can be used to produce current levels up to 20mA for each output from a 2.7V to 5.5V input. A serial control interface is used to enable, disable, and set the LED drive current for 32-level logarithmic scale LED brightness control. The converter has a thermal management system for protection in the event of a short-circuit condition on any of the output pins. Built-in soft-start circuitry prevents excessive inrush current during start-up. The shutdown current is less than 1μA.In the text, the basic 1.5X charge pump operation principle and performance parameters are given first. Then the systemic structure using linear mode is designed according to the comparison of skip mode and linear mode, as well as the need of invariable current source output. In sub-block circuit section, the typical circuits including bandgap reference, thermal protection, error amplifier and soft start are introduced. The basic principle and main parameters of every sub-block circuit are noted and the simulation results are given at the end of each segment(The system stability involving error amplifier is described particularly).Based on the charge pump principle analysis and circuit design in the chapters, important characteristics of the monolithic circuit are simulated by applying HSPICE. The simulation results indicate that both function target and performance characteristics meet the designable demand very well.