Chassis Ground layout for better ESD and EMI compliance

Mark · 2011-05-19T17:44:57+00:00

I have 2 USB, 2 Ehthernet and 2 RS232 connectors on the PCB. USB connsare one side, Ethernet conns on the 2nd side and RS232 on the 3rd sideof the board. All are through hole connectors and on top layer withseparate chassis ground area on each side for connectors shields. So Ihave three chassis ground islands on th board for three sets of theseconnectors. If we have to connect the chassis ground to the signalground through 1M Resistor and 1nf/2KV capacitor, which of thefollowing is better and why.1) keep the 3 chassis ground areas separate and connect each of themto the signal ground through 1M Res and 1nf/2KV cap. In this casethere will be 3 pairs of 1M and 1nf in parallel. Is this an issue?2) Have one chassis ground covering all three sides of the board andconnect to the signal ground with 1M Res and 1nf/2KV cap.3) What is the better place to connect the chassis ground and signalground? Is it at the power supply return?4) I have seen one reference design on the net with power supplyreturn and connector shields connected together in a copper area andthis copper area connected to the signal ground through a ferritebead.It is an 8 layer board with two signal ground planes and chassisground on all layers beneath the connectors stitched together atmultiple places with vias.Thanksmark

May 19, 2011 82 Replies

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Joerg 15 years ago

An engineer friend summed it up this way when he came back from a long problem-hunting trip: "Once I saw numerous crushed beer cans and cigarette butts in the bottom of the electrical cabinet I new the reason" :-)

Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

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John Larkin 15 years ago

We installed one system in Nigeria and found much worse stuff in the bottoms of rack cabinets.

John

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krw 15 years ago

there's

That's easy to say, but when the distribution system is in another building, or worse, a truck (generator) parked out in the parking lot, things can get quite ugly.

10-4 on that.

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