4-Channel Charge Pump White LED Driver Design

Nowadays the backlit of LCD display from the previous cold cathode fluorescent lamp (CCFL) is replaced by backlight LED.But as a portable LCD backlight white LED lights, the pressure drop of lithium batteries and portable power supply products are similar,in the process of using lithium batteries, as the battery voltage drops, it needs a boost converter to solve white LED's forward voltage problem.DC-DC boost generally use capacitive and inductive two ways to accomplish.This design mainly implements a capacitive charge pump boost white LED constant current driver circuit.The whole circuit drives four white LED lights,using 1X/1.5X way will resolve the problem of LED's forward voltage drop, but also ensure the highe power efficiency of the charge pump. It works in a fixed frequency of 1MHz, using off-chip resistor to set full scale LED current. External control terminals of two digital signals controls the chip off or the choose of LED three levels of brightness,and by the two chip resistors side or access port , the PWM LED dimming can be achieved. The chip also has a soft start, output overvoltage protection, thermal shutdown, undervoltage protection and some functions.Paper first describes the working principle of the LED driver, which gives the entire chip system architecture. Then it describes the design principle of the charge pump circuit and the specific implementation. In the sub-module design, it contains the bandgap reference, oscillator, current management circuitry, soft start, thermal shutdown and other five sub-modules. Finally, through Cadence Spectre platform and CSMC CMOS 0.5 1P2M model database,the simulation and verification of the overall circuit performance indicators and key parameters is done.