Design Of A High Performance Buck DC-DC And LDO Dual-output Controller

The paper is based on the project of the Institute of Electronic CAD,"Theoretical research on the key technique and the design for power management ICs". A high performance Buck DC-DC and LDO dual-output controller named XD8912 is proposed in this paper.Firstly, the current situation and trend of development of power management technique are briefly introduced in this paper. Then, the basic structure and operation principle of the linear voltage regulator and the switch converter are discussed. Moreover, the principle and loop stability of voltage-mode PWM DC-DC controller are thoroughly analyzed. Finally, the design of XD8912 is described in detail, including definition of the IC specifications, analysis of the electrical characteristics, implementation of subsystem circuits and simulation of the whole chip.XD8912 integrates both the large output current, high efficiency Buck PWM controller and the low current, low noise linear regulation controller. So it is an ideal supply for high performance graphics cards, motherboards and etc. By using the synchronous switch to substitute the Schottky diode, the efficiency of the chip has been increased greatly. In the chip, trimming circuit is designed to improve the accuracy of the voltage reference. Internal frequency compensation circuit is used to replace the external compensation capacitor and enhance the integration of the chip. Furthermore, protection circuits are integrated in the chip,such as over-temperature protection, under-voltage protection, over-current protection and so on.Detail theoretical analysis of system and main sub-blocks of XD8912 is made in the paper. Based on 0.6μm BCD process, the circuit design, pre-simulations and verifications have been completed by using the EDA tools of Viewdraw and Hspice. The simulation results show that all functions can meet the design requirements.