Design Of LED Backlight Driver Chip With Wide Boost Range Controlled By PW

Compared with other light sources,LED light-emitting diodes have many advantages such as longer service life,higher luminous efficiency,smaller volume,rich color gamut,energy saving and environmental protection.In recent years,with the popularity of mobile devices such as mobile phones and tablet computers,LEDs are widely used as display backlights for these mobile devices.To keep the brightness of the LED consistent,the drive power supply needs to provide a constant current.Switching power supply type LED drive is currently the mainstream LED drive method.Therefore,it is of great significance to research LED backlight driver chips.This paper introduces the development history of LED and the basic theoretical knowledge of switching power supplies.After reading the relevant literature,the topology,control mode,modulation mode and working mode of switching power supply are investigated.Based on the switching power supply boost topology,using PWM modulation and current feedback mode,an LED backlight driver chip is designed using 0.18μm BCD process.The chip has two dimming modes to adjust the brightness of the LED.The analog dimming is realized by changing the peripheral circuit,and the PWM dimming is realized by changing the reference potential of the input terminal of the error amplifier through the internal low-pass filter.The chip has various protection functions such as soft start,over-temperature protection,overvoltage protection,and over-current protection.This paper makes the following improvements based on the traditional switching power supply: the on-chip compensation is realized by using the capacitance multiplication technology,and the compensation capacitance is only 50 p F,which saves the chip area and reduces the number of peripheral devices.The error amplifier using the depleted MOS as the input pair tube is designed,so that the feedback voltage is as low as 300 m V when the chip is working normally,and it can be as low as 30 m V when dimming,which can effectively reduce power consumption.This paper completes the design of the chip frame structure and each sub-module,theoretically analyzes the stability of the current loop/voltage loop of the chip and designs compensation schemes respectively,and selects some important sub-modules to introduce their analysis in detailed designing process.After completing the design of each sub-module,use Cadence software to simulate and verify the overall function of the chip.The simulation results show that the input voltage range of the chip is 2.8-5.5V,the output voltage can reach up to 28 V,the operating frequency is 1MHz,the typical value of the output LED driving current is 25 m A,the output voltage ripple is lower than 30 m V under various conditions,and the output current ripple is lower than 0.2m A;the chip can use a DC voltage of 0-2.8V for dimming.A PWM signal with a frequency greater than 500 Hz can also be used for dimming,The current varies from 0 to 25 m A during dimming,and both dimming functions work normally.The simulation results of the chip are consistent with the expected design indicators and meet the design requirements.Finally,the improvement of the system performance by the slope compensation circuit and the soft-start circuit is verified,and the layout design of the chip is completed.The chip designed in this paper can stably drive 2-8 white LEDs in series and can be widely used in the screen backlight drive of various portable mobile devices.