Figure 17-3. Grounding Recommendations for External Connectors
13. In applications where the AC chassis ground is available, it is strongly recommended that the digital signal
ground and AC chassis ground NOT be connected and are separated by at least 3.175 mm (i.e., 0.125
inches), for the 1
1-12 KV spark gap isolation to meet IEC61000-4-2 level-4 ±8 KV contact discharge.
Peripherals, such as USB, Ethernet, SD memory card holders, RS232, and CAN, the connector cases are
electrically isolated from the signal ground. The case should be connected to the AC chassis ground whenever
available (i.e., Earth Ground), to shunt the high voltage discharges to the earth ground harmlessly and not into
the digital or analog ground circuitry.
Note: In the figures the ground plane is always continuous under all the high-speed signal connections of the
peripheral connector, but the connector case is isolated to the outer AC chassis plane.
Comprehensive PCB Layout Guidelines and Recommenda...
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