Chassis ground and Digital ground connections using RC

[FreshmanNewbie]

Please see the below connections:

I have seen long back another board and chassis ground connection with an RC with a different set of RC values.

My question is: What determines the correct RC value? Is there a correct one? Or does it depend on the interface such as USB or Ethernet?

 

[KlausST]

Hi,

I´d say there is no "one and only correct".

The capacitor is there to build a low impedance path for high frequencies.
So it´s on the application
* what frequencies you want to focus on
* what impedance you want at these frequencies

and the resistor is there to suppress static charge.

Klaus

 

[FreshmanNewbie]

Hi,

I´d say there is no "one and only correct".

The capacitor is there to build a low impedance path for high frequencies.
So it´s on the application
* what frequencies you want to focus on
* what impedance you want at these frequencies

and the resistor is there to suppress static charge.

Klaus

Thank you for the clarification. Ok, so the capacitor I need to select based on the frequency. So, I need to calculate based on the Xc = 1/(2pifC) formula, right? In that case, what should the frequency I need to be focusing on 100/1000BASE-TX ethernet and USB 2.0/3.0? Any idea on this?

Also, can you explain how the resistor helps to suppress static charge and how to arrive at the value of R? Which formula to use?