Protecting the Universal Serial Bus from Over Voltage and Overcurrent Threats

This application note addresses the various requirements for protecting the Universal Serial Bus (USB) from overcurrent and over voltage environmental threats.The solutions presented cover both USB 1.1 and the higher speed USB 2.0 circuitry. Specific emphasis is placed on USB 2.0 with information directed at hot connection over current conditions and electrostatic discharge (ESD) induced in the USB system. The USB specification provides a uniform protocol for the addition and configuration of computer peripherals. USB is designed around one uniform port size and a matching connector. It uses the concept of a single host and multiple hubs designed to provide uniform and simple methods for adding and connecting various peripherals. The goal of USB is to reduce the number of cable connections and configurations. A single USB port has the capability of driving up to 127 USB peripherals such as mice, modems and keyboards (see Figure 1). Additionally, a single hub permits the connection of several USB devices by providing power through the communication cable itself, eliminating the need for individually powered peripherals. It also allows mixed high-speed communications between USB and other protocols such as Ethernet, DSL, ISDN or satellite communications