Analog Devices: CN0158 Reference Design for Universal Serial Bus Hub Isolator Circuit

Kit Overview

The universal serial bus is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232RS-232 and the parallel printer port because of superior speed, flexibility, and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use the bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

The goal of the application circuit (EVAL-CN0158-EB1ZEVAL-CN0158-EB1Z) is to isolate a hub as if it were a full speed peripheral device. The hub or host function requires that 2.5 W of power be available to each downstream port. Power to run the downstream side of the isolator and power the hub and ports is provided as part of the solution.

In this USB Hub Isolator Circuit (EVAL-CN0158-EB1ZEVAL-CN0158-EB1Z), the ADuM4160ADuM4160 is designed primarily as an isolation element for a peripheral USB device. However, there are occasions when it is useful to isolate a host device. Several issues must be addressed to use the ADUM4160BRWZ.ADUM4160BRWZ. for this application. Whereas the buffers on the upstream and downstream sides of the ADuM4160 are the same and capable of driving a USB cable, the downstream buffers must be capable of adjusting speed to a full or low speed peripheral that is connected to it.

Unlike the case of building a dedicated peripheral interface where the speed is known and not changed, host applications must adapt. The ADuM4160ADuM4160 is intended to be hardwired to a single speed via pins; therefore, it works when the peripheral plugged into its downstream side is the correct speed, but it fails when the wrong speed peripheral is attached. The best way to address this is to combine the ADUM4160BRWZ.ADUM4160BRWZ. with a hub controller.

The upstream side of a hub controller can be thought of as a standard fixed speed peripheral port that can be easily isolated with the ADuM4160ADuM4160, whereas the speed of the downstream ports is handled by the hub controller. The hub controller converts peripherals of different speeds to match the upstream port speed.

Key Applications: Medical and industrial applications