EVAL-CN0159-EB1Z: Isolated USB Cable

The goal of this application circuit is to isolate a peripheral device that already implements a USB interface. It is not possible to make a fully compliant bus-powered cable because there are no 100% efficient power converters to transfer the bus voltage across the barrier. In addition, the quiescent current of the converter does not comply with the standby current requirements of the USB standard. This is all in addition to the speed detection limitations of the ADuM4160. What can be achieved is a fixed speed or switch-controlled speed cable that can supply a modest power to the downstream peripheral. However, it is a custom application that is not completely compliant with the USB standard.

The ADuM4160 provides an inexpensive and easy way to implement an isolation buffer for medical and industrial peripherals. The challenge that must be met is to use this to create a bus-powered cable isolator by pairing the ADuM4160 with a small isolated dc-to-dc converter such as the ADuM5000. As with isolating any device, the services that the ADuM4160 provides are as follows:

• 1. Directly isolates, in the upstream, the USB D+ and D− lines of a cable.
  

• 2. Implements an automatic scheme for data flow of control that does not require external control lines.
  

• 3. Provides medical grade isolation.
  

• 4. Supports full speed or low speed signaling rates.
  

• 5. Supports isolated power delivery through the cable.