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I am using micro USB socket to charge the battery in one of the device and now we are planning to go for CE certification for which we are doing EMI/EMC test. For the ESD IEC 61000-4-2 (+/- 6 kV contact +/- 8 kV air) test standard. The outer shied of micro USB should be connected to ground. But in one of the reference diagram it is connected to ground via some resistor and TVS diode. (Schematic attached below).

Should I connect micro USB outer casing to ground or connect it via some resistor to ground and then employing TVS diode as shown in the schematic?

I think using the second technique the ESD pulse would not affect the common ground and will not affect the sensitive IC connected to the common ground.

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I usually connect the shield to a chassis ground (not PCB ground) this way any ESD currents are shunted to the case and don't create common mode noise (or voltage spikes) on the PCB and the ESD currents are kept well away from any electronics.

I have also had issues with external cables and their connection to the chassis. The best place for the ESD spike current to return to (if the voltage is applied on the shield of the cable) is to the chassis. I have had issues if the shield of the entry cable was not tied well enough to the metal chassis of the instrument. Once we tied the chassis to the USB shield the currents returned through the chassis and stopped causing a failure of the test.

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I think the general idea is to shunt the current away from the PCB before it ever becomes a problem (with a chassis ground (through a fastener) on the PCB separate from the PCB ground), if your design does not permit this, sometimes the way to go to slow ESD spike down and create some impedance to reduce noise is by a resistor as shown above. ESD testing can be tricky and it really depends on the entire product, the best way to test is to have some options to see what works, because I've had designs that work well in one product and do not work well in another. Make sure you also have an ESD filter on your data lines also (which you may have but don't show)

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