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GND For Connector Shielding

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tiwari.sachin

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I have 4 connectors

1. Power
2. USB
3. Ethernet
4. USB

All placed in a proper straight line so that when placed in a enclosure, the same are properly flushed.

The body of the connector (Shielding) is done for each of them via a 0.1uF and 1M Resistor to GND.

The outer casing (or the part where these connector sit is of a metal)

Because the cutouts are perfectly in line with the connector size. The metal touches the connectors outer body.


I notice that the board is working fine when i am using it without putting it on the casing but the moment i use the casing, USB doesnot work (I will have to remove it completely and reprogram using a external program) and it works again.

Why could this behavior be happening??

Image of sch and metal slot shown
 

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    GNDING to PLATE.png
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You’ve got three different grounds shown there, that’s a little confusing. Where do they all go? Where do the shield connections of each connector actually go besides ground?
 

All the shield has to be ground... via a resistor and cap in parallel as shown for ethernet and serial.

I have unfortunately connected usb directly to ground... probably missed it

Power ground point in the return path
He again I needed to have a parallel resistor and cap for shield which I missed.

So it it ok to have it for all connector shields and same for top metal plate
 

Should they be??
What's the best practice?

Will there not be issues with esd if connected directly
 

Hi,

ESD? No. This is electrostatic discharge.

EMC. Electromagnetic compatibility.
A metal case should be considered as a faraday cage. Where the whole case should have the same voltage at any place.
I'd use a common shielding_GND (on the PCB)!for all connectors. With one RC to the system_GND.

But I see no problem with your circuit for now, since the C should act as short circuit for HF.

There rather is another problem.
* other connections to the GND or case, like a GND loop via earth_GND.
* or HF noise introduced by an external device (like an SMPS)
* maybe a soldering fault or PCB fault that generates a short circuit between USB_shield and USB_+5V .... or something similar.
* maybe you don't have a solid GND plane on your PCB ... causing a loop via GND traces on your PCB.

Klaus

Btw: Yes, the different GND symbols are confusing.
* if they refer to the same signal, then use the same symbol.
* if they don't refer to the same signal, then give information where the belong to / how they are used.
 

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