FEDEVEL
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noisepic , 08-23-2018, 12:08 AM

Could you help shielded gnd for rj45 connector should connect by a capacitor or inductor to system gnd?

robertferanec , 08-24-2018, 12:28 AM

Connection of shield depends on the whole system and product (e.g. is the product in plastic box, metal box, is placed inside bigger system, does it connect to other devices - are these devices placed close or they are placed far away from each other, is the whole system powered from one main source or all devices plugged into one system are powered from different sources, is it battery powered device, etc ....).

If you are not sure what component to use to connect Shield, in your PCB place there some footprints and during EMC/EMI/ESD testing try to fit there different components (e.g. 0R, BEAD, Capacitor, ...). In the final product use the component with best results from the tests.

PS: In many of our boards we use direct board ground connection to Shield, however this is for the processor boards which we design. In your situation it may be different.

noisepic , 08-25-2018, 11:06 PM

My product is in plastic box. But it's in opposite way when we place: bead will stop high freq into our gnd system, but capacitor will stop the low freq and allow high noise to our system.

Might be ferrit beat should be correct!

robertferanec , 08-27-2018, 12:20 PM

As I suggested, maybe leave there more footprints and try different options. BEADs are not always solution - for example, we had a case when a BEAD was problem during ESD testing.