Research And Design Of High Efficiency Boost WLED Driver IC

In recent years,WLED gradually becomes the best choice of the LCD backlight with its high luminous efficiency and long life,which is widely used in display screens with various sizes.The WLED driver chip is the key component in the entire backlight system.With the wide application of the portable electronic devices,the better performance of LED driver are required,these are better drive capability,higher output efficiency and fast dimming performance.In this paper,based on the request of portable electronic devices backlight,the design of a fast dimming boost WLED driver with high efficiency is presented.Based on 3-channels constant current structure,the boost DCDC converter with asynchronous peak current control mode is used to complete voltage pre-regulation and the precise adjustment of current in each channel is done with current regulator.The circuit averaging method is used to complete the modeling analysis of voltage control mode and peak current control mode DCDC converter.Based on the result of modeling analysis,a Type II compensation network is designed to complete the system compensation.A large on-chip compensation capacitor is achieved by capacitance scalar circuit,which effectively saves the chip area.In order to avoid color excursion,the system uses a direct PWM dimming scheme.In the meantime,an instant-restoration technique is proposed to achieve fast dimming,different from conventional PWM dimming which cuts off the feedback loop,it holds the dimming ON period system state during the dimming OFF period and instant restores original system state during the dimming ON period.At the same time,the power consumption of the chip is analyzed in detail.A comparison of theoretical and practical consumption is presented.A constant current drive scheme with minimum feedback voltage selecting is used,compared with conventional fixed output voltage constant current drive scheme,which ensures the normal operation of each channel and effectively reduces the system power consumption.Then,a PWM dimming method with reusing MOSFET and a circuit setting a variable reference voltage are used to reduce the consumption of current regulator and improve system efficiency.Based on the characteristics of LED,a new LED current soft-start circuit adjusted by current regulator is designed to eliminate the unexpected overshoot current.The proposed LED backlight driver is designed with CSMC 0.25?m 40 V BCD process,and verified by Cadence Spectre simulator.The LED driver supports an input range from 2.7V to 5V,and a maximum output voltage up to 36 V.It can drive 3 strings with 10 WLEDs per string,each string provides up to 30 m A drive current.The maximum power conversion efficiency is 91.6% at a 5V input with 60 m A total load current.The dimming ratio of the LED backlight driver using the proposed instant-restoration technique is calculated to be 2000:1 at a dimming frequency of 120 Hz.The under-voltage-lock-out circuit,over-voltage-protection circuit,over-current-protection circuit and some other protection circuits are also designed to improve the stability of the LED driver.The simulation result shows that,all the function and performance can works well.At last,the layout of the chip is completed with the area of 1501?m×1310?m.