A Dual Usb Power Switch Design

Universal Serial Bus (USB) is an emerging standard for data transmission. With its "Plug and Play"feature and port expansion feature, USB is becoming more and more widely used. Choosing the right power management strategy is essential to a USB system which functions well. This thesis is about the USB power switche, which is a crucial device in USB power management systems. A dual channel USB power switch is successfully designed in this thesis. USB Specification 2.0, released in April 2000, has much higher data transmission speed comparing to its former edition. Corresponding changes also can be seen in chapters about power management. In this design, function definitions and parameter presettings are fully compliant with USB 2.0 specifications. The designed chip not only has basic functions such as current limiting, switching and fault flag, but also has enhanced functions such as soft start, 1ms fault flag delay, over temperature shutdown and under voltage lockout. Critical device parameters are also presetted carefully. The supply voltage range is 2.7V-5.5V, the maximum operating current is 200μA, and the maximum on resistance is 140 m?. The chip guarantees a continuous output current of 500mA while limits the current to no more than 1A typically. The under voltage lockout threshold is about 1.8V. When building the circuits, twelve function blocks are defined according to the whole chip function, and then functions and parameters of each block are defined before they are embodied with practical circuits. All sub-circuits are derived carefully and verified by HSPICE. In whole chip simulation, all possible application situations, such as shorted output and under voltage, are well simulated and verified. In chapter 2, the overall working principles are introduced. Chapter 3 deeply analyzes several sub-circuits and gives their simulation results. Chapter 4 is some important curves of the whole chip simulation. Those sub-circuits which are designed mainly by the author are particularly analyzed, and simple introduction is given about other sub-circuits. Circuit analysis and simulation results show that the design has been successfully completed.