FEDEVEL
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Nixy , 08-07-2024, 02:04 PM

Yes it's this old chestnut again, What to do here?

My integrated magjack has integrated transformer with built in 75R bob-smith termination & a 1000pf/2KV capacitor in, with the free end going to pin 10 of the RJ45 connector (marked as ground).

As this is going into a metal enclosure my thoughts are to connect both pin 10 and the chassis connection pins together and attach them to a metalised mounting point on the board so they have good connection to chassis ground.

There is then the question of whether to put a connection in between digital 0V and chassis ground? Connect directly or use a 1nF 2kV cap ?

What do the pro's do here?

QDrives , 08-07-2024, 09:27 PM

Isn't pin 10 for the PHY connection too? As in 'the' Gnd?
I have connected shield to Gnd as well as via capacitor close to the connector on some designs.
Add a high ohmic resistor parallel to the capacitor to drain any (static) voltage build-up.

Nixy , 08-08-2024, 09:48 AM

Thanks for the reply!
No Pin 10 is just where they brought the bob-smith and capacitor out, I think what we're going to do is connect that pin and the two metal lan case lugs together and through to a metal mount for chassis connection, then put 2x 1nF/3kV caps to connect that back to the 0V

This was interesting

https://www.eevblog.com/forum/projects/bob-smith-chassis-connection-for-plastic-enclosure/

QDrives , 08-08-2024, 09:07 PM

If pin 10 already has the capacitor, I would just connect that to Gnd.
The shield of the connector to your own capacitor to Gnd.