Abstract
A bi-frequency PFM controlled boost DC-DC converter, combining the respective advantages of the conventional PWM and PFM, is designed and implemented in this paper to improve the electro-magnetic interference (EMI) and efficiency of the system in a wide load range. The spectral energy of proposed bi-frequency PFM controlled converter is distributed to more frequency points to decrease the discrete harmonic peak, achieving low EMI and noise level. By detecting load changes, the proposed converter operates at a corresponding frequency at light load or heavy load and switches between the two frequencies at medium load to improve full-load efficiency. A control IC for the boost converter has been fabricated in Founder Microelectronics 0.5 mu m CMOS process. The layout area is 800 x 640 A mu m(2). Experimental results show that the full-load conversion efficiency is over 80 %, and the quiescent current is under 10 mu A. Meanwhile, the converter has fine EMI characteristics.