This paper describes the design of DC-DC converter for driving LCD (Liquid Crystal Display) of mobile phone, PDA (Potable Data Assistants), and so forth. This converter operates in the PFM (Pulse-Frequency Modulation) mode at 500KHz ranges and in the PWM (Pulse-Width Modulation) at 5MHz switching frequency. While the conventional converter operates at lower frequency than this converter, the conventional converter needs higher capacitors and inductors than this converter. So this converter feeds regulated power to the output a inductor having low inductance. In the PFM mode, this converter uses the 200ns minimum off time circuits and the variable current limit circuit. In the PWM mode, this converter uses the leading edge modulation scheme to broaden the cross-over frequency and reduce the effect of positive zero in the Boost DC-DC converter system. This converter is fabricated by using 0.8um CMOS technology. The efficiency is about 90% from 3.3 volts input voltage and the ripple is about 0.5%.
