We all love USB. It is well supported across many platforms, easy to work with, and even able to provide a little power to the peripheral. However, the quirk of USB is that peripheral must share ground line with the host. The host is usually a PC and very often a desktop, which means it’s USB ground is electrically connected to earth ground in the wall outlet. It works fine most of the time, but not always.
Sometimes we prefer our ground separate. It happens when PC/earth ground is too “dirty” and we don’t want our circuit to pick up this dirt. Sometimes our device’s ground is not too good or even dangerous if connected to earth ground. Sometimes we are fighting ground loops. In any of this cases we want our USB isolated from the host.
Isolation improves common-mode voltage, enhances noise rejection, and permits two circuits to operate at different voltage levels. It also saves equipment (sometimes), especially PC-based measurement instruments like USB oscilloscopes, logic analyzers, as well as PC itself. It is also very useful in industrial setting, that probably why industrial USB isolator solutions cost between $200 and $400. While looking for a solution for my lab, I found interesting USB isolator part, recently released by Analog Devices, and decided to give it a try.
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