John:
If the discharge is interrupting the signal then the signal low and the shield
ground are being combined at some point. USB is a differential signal. Sounds
like something is connected wrong at either the mouse end or the USB receiver
chip end.
John Cochran wrote:
During testing of an industrial control system, with a custom stainless
steel
USB mouse, ESD testing failed. The standard used was IEC 61000-4-2,
Electrostatic Discharge. When a -4KV discharge was applied to the metal
housing of the mouse, the mouse and/or USB keyboard would stop functioning.
The function returned after testing, only if the USB connection to the
computer was broken and connected again. Suspected the ESD charge was
disrupting the USB communication in the computer, since the cable shield is
the only path to earth ground. Tried to break the cable shield and connect
the mouse end to the enclosure (earth ground), with no improvement. Looped
the cable through an Intermark RFC-20 ferrite which helped to pass testing,
marginally. Does anyone have any good suggestions for eliminating the
interruptions causes by a contact ESD discharge on a metal shelled USB mouse?
John Cochran
215-443-3400 x193
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