Design Of Synchronous Buck DC/DC Chip XDJ6348 With LDO Mode

The paper is based on the project"Theoretical Research and Design of Key Technique for Deep-sub Micron Power Management IC and Mixed IC"and mainly deals with the design of DC/DC converter IC XDJ6348 with LDO mode.This paper analyses and studies the basic principles of buck DC/DC converter and LDO which is the theory guidance of the design and the implementation of XDJ6348. As a result of the adoption of current mode PWM control for DC/DC converter, the transient response speed of the supply voltage and the load's variety become more faster. In order to overcome the disadvantages of current mode control when the duty cycle is greater than 0.5, such as instability of open-loop, a slope compensation circuit is designed. 100% duty cycle of the chip XDJ6348 provides low dropout operation, extending battery life in application systems. XDJ6348 can switch to LDO work mode when the load current is less than 3mA in order to improve the work efficiency of the chip under low load current and maintain low output voltage ripple. Linear regulator operation can be set to always ON, OFF or automatic turn on/off according to the load current. The over-temperature protection circuits are designed to shut down the chip when the operation temperature is too high to protect the IC to be damaged. When all of the operation condition is recovered, the chip starts up automatically. With the internal synchronous switches to take place the external Schottky diodes, the XDJ6348 reduces the power consumption and saves the PCB area and system cost.The design of XDJ6348 is based on the 0.6um CMOS process. The simulations and verifications of the whole chip have been completed.