USB Shell/Shield connection

[KMC500]

Hi All,

I have an ESD failure when doing contact discharge @-2kV directly on to the shell of my type-B USB connector.

I use a Wurth 824011 TVS diode array rated at +/-8kV for contact discharge. My Shell is terminated to ground via a parrallel 1MR/4.7nF capacitor.

Assumption is that my ESD failure is related to the negative discharge getting directly on the signal GND line and causing device failure. I have now disconnected the parrallel termination, isolating the USB Shell from signal GND and the instrument now passes ESD testing.

I read in other forums that this is a grey area on how the shell connection should be configured, in many cases people say that the shell connection should be terminated to signal GND on the HOST side only.

Just looking for a little clarity here.... Hope you guys have experience in these issues and the best way to handle.

Many thanks in advance,

Kev

[Jan Axelson]

Yes, the USB 2.0 spec says only:

The shield must be terminated to the connector plug for completed assemblies. The shield and chassis are
bonded together. The user selected grounding scheme for USB devices, and cables must be consistent with
accepted industry practices and regulatory agency standards for safety and EMI/ESD/RFI.