The Design Of The Synchronous Rectification Buck DC-DC Converter Based On Peak Current-Mode

As consumer electronic devices become more and more popular, power management ICs is widely used. The switch-mode DC-DC converter is a kind of high- efficiency switch-mode power converter. It has many good qualities such as high efficiency, steady power, small ripple, high integration and so on. It is widely used in all kinds of portable electronic devices. According to application requirement of portable electronic devices, through system design, circuit design and performance simulation, a peak current-mode synchronous Rectification buck DC-DC converter with current sensing technology on chip is realized in this thesis.This thesis analyses and studies the basic principles and the key techniques of peak current-mode synchronous Rectification buck DC-DC converter, which provides the theory guidance for the whole system design. Base on theory studing, the peak current-mode PWM controlling scheme is adopted in system design. By using on-chip a power MOSFET with low on-resistance and a accurate low-power on-chip current sensing circuit provide fast precise current-mode controlling.Therefore, the transient response peed become faster as the supply voltage and the load variety. The thesis analyses instability of peak current-mode controlling PWM buck DC-DC converter and principles of slope compensation, too. In order to meeting the requirement of slope compensation, a simple linear slope compensation circuit which can overcome the disadvantages of peak current-mode DC-DC converter when the duty cycle is greater than 0.5, such as instability of open-loop, sub-harmonic oscillation and an increased sensitivity to noise is designed in the thesis. In addition, a single-Edge Pulse-Width Modulator is designed with skipping frequency function, which can enhance efficiency of the converter when load is very small. The oscillator which has tow loops to charge and discharge by a constant current source can generate constantly and high-frequency clock in the single-Edge Pulse-Width Modulator. The high switching frequency (1MHz) allows the use of lowprofile inductors and ceramic capacitors to minimize the thickness of LCD panel designs。At last, Based on the circuit principle analysis, the sub-block circuits and the whole controlling circuit were simulated by applying the EDA tool HSPICE and standard 0.35-μm CMOS process. The simulation results indicate that the converter can operate from 600 kHz to 1.2MHz with supply voltage frome 2.6 to 4V, which is suitable for single-cess lithium-ion battery supply applications. The output ripple voltage is about 20mV with a 10-μF off-chip capacitor and 4.7-μH off-chip inductor.