Connection of ESD return path the System GND

[kays]

Hi all,

This is my first post to the forum and I would like to say a big HI for all fellow electronics aficionados.

In my current design I have one RJ45, one RS232 and two RS485 ports. I have TVS diodes CDSOT23-SM712 for serial channels and ESD7104MUTAG for Ethernet port. Now I have connected the ESD GND of the TVS to a separate GND island (referred to as CHGND) and then AC coupled that to System GND via 1n (2kV) parallel with 10MEG (both 1206 package). My idea is to not directly couple noise from ESD return to system ground. This is also suggested in Microchip App note AN2054.

My system is powered by 12V DC power supply coming from a mains Flyback or external 12V DC power supply. I dont have a Chassis GND or Earth. The enclosure is ABS.

Now my review engineer is against that, pointing out that once a ESD strike comes in, it lifts the CHGND high (or low) until the bleeding resistor discharges that. This makes the line we are trying to protect experience the high voltage relative to GND. (I simulated this for 8kV HBM pulse and the voltage rise was about 770V) Also not working for repetitive strikes.

What do you guys think? Is it better to directly connect ESD return to system GND or AC couple?

Thanks in advance,
Kay