Drive Chip Design For High Efficiency Synchronous Rectification Step-up LED Flash

As the rapid development of portable electronic devices in the direction of the miniaturization,multi-function,low power consumption,etc,power management integrated circuits(PMIC)with high performance has become the hotspot of power electronic research.Switch mode power supply(SMPS)has advantages of high convert efficiency,small size and loaded capability,which has become the mainstream power management technology.Synchronous rectification technology can further improve the conversion efficiency.Firstly,this thesis discusses the development,current research state and common topologies of the SMPS briefly,after that the operating mode and modulation process of the boost converter are analyzed in detail.Then the design parameters and requirements of this boost convert are provided.At the end of this thesis,a peak current control PWM modulation boost LED flash driver for smartphones is presented.Unlike the single working mode of traditional boost DC-DC converter,the chip is presented boost mode and pass mode.This method not only ensures the normal operation of the chip within 2.5V-5.5V,but also reduces the amounts of power MOSFETs,power dissipation and area.In case of the inrush current and overshoot voltage during start-up,a novel soft-start circuit without soft-start pin is applied to the chip by making power PMOS as current source to pre-charge output capacitor,and this method ensures the rising stability and starting quickly of output voltage.A novel power transistor logic driver circuit is presented to increase the convert efficiency.This method reduces the dead time and leakage of the substrate current effectively,which makes convert efficiency improves obviously.The chip has been successfully taped out and fabricated with 0.13μm Magnachip CMOS process,which is integrated with bandgap current reference,soft-start circuit,oscillator,current driver circuit,etc.Due to ensure the reliability of the chip,this chip also integrates overvoltage protection circuit(OVP),overcurrent protection circuit(OCP),overtemperature protection circuit(OTP),under voltage lock out(UVLO),etc.This thesis also discusses and analyzes some critical modules carefully,provides the simulation results which verifies the feasibility and validity of the whole circuit and protection function.The lab test results show:the function of this chip is ready within 2.5V～5.5V:The chip can start up stably in 128μs.and the output voltage rises smoothly without overshoot;The output current accuracy is less than ±6%,and the average power conversion efficiency can reach more than 85%.