Design Of Multiple Outputs Buck DC/DC Converter IC

On the basis of the project of the Institute of Electronic CAD,"Design and key theoretical research of multiple outputs DC/DC regulator", a dual outputs peak current mode synchronous buck DC/DC converter XD1124 is designed and a deep study of multiple outputs current mode DC/DC theory is carried out. The simulation of the whole chip has been completed, and the simulation results show that specifications are met.This paper analyses the basic principles and control modes of DC/DC converter, which is the theory guidance of the design and the implementation of XD1124. By adopting the technologies of synchronous rectification and two optional operation modes at light loads, the efficiency of the chip is enhanced at whole load range. Two regulators are designed in one single chip, and work independently. To further maximize battery life, when input supply voltage decreases towards output voltage, the duty cycle increases to 100%, which is the dropout condition, and the PMOS switch is turned on continuously. As a result of the adoption of current mode control, the transient response speed of the supply voltage and the load's variety becomes much faster. In order to overcome the disadvantages of current mode control when the duty cycle is greater than 50%, such as instability of open-loop, sub-harmonic oscillation and sensitivity to noise, a slope compensation circuit is designed. A clamp circuit is also designed whose threshold can be adjusted with respect to the magnitude of the slope compensation signal so that a substantially constant maximum current limit of the regulator may be remained at greater duty cycles. Over and under voltage protection circuits, over temperature protection circuit and other protection circuits are designed, which make the system more reliable and stable.