The Temperature Compensation Technology Of White LED Driver Chip For Portable Equipment

As one of the most promising light sources, White LED has many advantages, such as high luminescence efficiency, low power consumption, small size, long life period etc. In order to give full play to their advantages, a good driver is indispensable. Now the white LED driver chip has become a star in portable equipment field.In the main part of this thesis, firstly, the whole chip's structure is constructed. Using inductor step-up converter to drive White LED is a major method for portable applications. In the process of chip design, the current mode PWM control, ambient temperature limiting technology and two dimming methods were used for increasing the chip's speed, reliability, economic and applicability.And then, use the temperature compensation technology in the sub-circuits designing such as ambient temperature limiting circuit, bandgap reference circuit, over temperature protection circuit, and the simulation results are given. The ambient temperature limiting circuit can dynamically adjust the chip's output current according to the current temperature curve of white LED. Therefore the highest output current can be safely set over the entire operating temperature range, thereby allowing fewer LEDs to be used for normal display brightness which reduce the cost of application. Moreover, this circuit can protect LEDs from over-driving during high ambient temperatures, so it enhancing the chip's reliability.Finally, use software Cadence Virtuoso and process Jazz BCD05 2P3M BiCMOS for the whole chip simulation and analysis: the soft start delay attains 1.9 ms, the chip can drive up to 8 white LEDs at 26mA in 1 MHz switching frequency. The conversion efficiency is above 75% under moderate load and low input voltage, and the highest conversion efficiency is 86%. Analog dimming, direct PWM dimming and ambient temperature limiting functions are effective. The results show that the chip has achieved the expected demand.