Current Control Mode, White Led Driver Ic Design,

As the development of semiconductor materials, white LED has become the best selection for small color LCD backlighting. Due to characteristics of white LED such as large forward voltage and high temperature sensitivity, and necessity of uniform brightness requirement of the portable application, specially designed power management IC is needed. Current-mode DC/DC converter adds a current feedback loop on the base of voltage-mode control, achieving both current and voltage feedback loop control. Due to its characteristics of fast response, good stability, inherent current limiting, current-mode controller has been widely applied in power management circuits.The PWM current-mode DC/DC converter is firstly studied in this dissertation, after that, a high efficiency; current regulating boost DC/DC converter for LED driving is designed. A 1.2MHz oscillator and the building blocks for protection such as over current limiting, open-circuit load fault protection are also integrated. The LED load current is programmable with the range of 5mA and 40mA.The fundament principle of monolithic current-mode switching regulator is firstly introduced, which is followed by a comparison between current-mode and voltage-mode control scheme where the merits and drawbacks of both converters are discussed and analyzed in detail. Next, the global system architecture is presented upon the design requirements. Due to the fact that constant current is required for driving LED, as a result, different from conventional current-mode converter with both output voltage and inductor current feedback loop, the proposed converter adopt dual current feedback loop that both inductor current and output current are detected to provide a stable output current for LED. The system exhibits fast response for the load current disturbance and the system always operates at discontinuous conduction current mode so that no slope compensation is required and high efficiency will be achieved when driving 4 LEDs.The design and analysis of sub-block circuits are provide in the thesis where band gap reference, oscillator, current sensing and over current protection, LED load current...