GND For Connector Shielding

[tiwari.sachin]

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

 

[barry]

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?

 

[tiwari.sachin]

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

 

[betwixt]

Why are they not ALL connected directly to ground anyway?

Brian.

 

[tiwari.sachin]

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

Will there not be issues with esd if connected directly

 

[KlausST]

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.