Robert Oppenheimer

USB Tap noise sensitivity

Discussion created by Robert Oppenheimer on Jul 3, 2008
Latest reply on Jul 30, 2008 by Pascal Irrle

We were having several problems with a spontaneous target reset or loss of communication between the target and USB Tap when debugging a DSP56F8357. This became very obvious when we had one engineer performing ESD (electro-static discharge) testing on a system across the room from another engineer debugging with a USB TAP.  Quite often, on a discharge event, the target system would reset. Very strange since the two projects were on different benches and served by different electrical systems.


By adding a ground lug to the USB tap case and connecting it with a faston terminal and 18AWG wire to the target earth ground, all the reset and communication problems went away. We were shooting 10KV sparks repetitively to a system in close proximity (that would have made Marconi proud) with no USB Tap problems. Before the addition of case ground, even 4KV would cause problems from a further distance.


This would suggest that something is either weakly terminated or floating inside the Tap's case or that the case itself is not grounded to anything internal.