Demonstration circuit 590 is a USB-based digital controller with generic Serial Peripheral Interface (SPI) and Inter Integrated Circuit (I2C™) ports. It is designed to mate with Linear Technology’s family of QuickEval™ demonstration boards. The demo board is fully isolated from the host PC’s ground, and in many cases no external power source is required. The evaluation software automatically detects which demo board is connected and loads the appropriate control screen. This system facilitates quick performance evaluation of a variety of products, including ADCs, DACs, SMBus power control products, and others. Figure 1 shows a block diagram of DC590. Power and digital signal connections are made via a 14-conductor ribbon cable. In many cases the controller can provide power for the demonstration circuit as well as digital signals. The demonstration circuit connections are fully isolated from the host PC’s ground (earth ground.) Four of the fourteen ribbon-cable conductors are referred to earth ground. Thus the isolation barrier is not designed to withstand large potential differences.