Yes, I agree! But as you say, single point ground raises costs significantly.
And switching supplies can be 30 dB noisier when trying to restrict grounding
points.
Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email:
doug@xxxxxxxxxx Website: http://dsmith.org
On Thu, May 10, 2018 at 7:49, Grasso, Charles <CHARLES.GRASSO@xxxxxxxx> wrote:
Doug - Agree completely.
However there are some design guidelines (based on the final install
environment) that
REQUIRE isolation. At least thatâs what I ran into with some DO160 stuff.
At that point is massive shielding and filtering - no fun at all!!
Thanks
Charles Grasso
(w) 303-706-5467
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Douglas Smith
Sent: Wednesday, May 09, 2018 10:33 PM
To: leeritchey@xxxxxxxxxxxxx
Cc: joel@xxxxxxxxxx; gurushankara@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Logic ground and chassis/safety ground
Hi All,
I respectfully disagree with Leeââ¬â¢s comments. It almost guarantees an ESD
problem. I have fixed hundreds of ESD problems by connecting the two grounds in
as many places as possible.
Also doing so significantly reduces the cost of switching supplies operating
from the mains, lowering induced noise by 30 dB on average for a given supply.
I have lost count on this kind of fix.
One connection also guarantees the lowest resonant frequency of the chassis-PCB
resonant circuit (which WILL exist) and prevents the simple solution to kill
the Q of that resonance. Multiple connections raise this frequency but the best
is multiple connections and then to de-Q the resonance you will always have
between the PCB and the chassis.
After 40 years of fixing chassis-PCB interactions I have developed quite a base
of solutions.
Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email:
doug@xxxxxxxxxx Website: http://dsmith.org On Wed, May 9, 2018 at 10:12, ;
leeritchey@xxxxxxxxxxxxx <leeritchey@xxxxxxxxxxxxx> wrote:
There is no electrical reason why you need to connect these two. If you do
connect them, do it in only one place and do it with a DC connection. I make
that connection on the side of the PCB where the unshielded wires exit as a way
to minimize potential EMI escaping on those unshielded wires.
Don't know where all of the rules of thumb come from about capacitors and
multiple connections.
Lee RItchey
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf Of
Joel Brown
Sent: Wednesday, May 9, 2018 9:47 AM
To: gurushankara@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Logic ground and chassis/safety ground
Unless you have a requirement or other reason to keep them isolated It would be
best to connect them together.
If you decide to keep them them isolated then add multiple capacitors between
signal and chassis ground at each chassis connection point that can be
populated with different value capacitors or zero ohm resistors. Another option
is to have a chassis ground plane layer in your PCB that is connected to signal
ground at multiple points with capacitors. If you don't have a solid RF
connection between signal and chassis ground then there can be an RF potential
between the two grounds that can radiate if you have antenna structures such as
slots in your enclosure or external cables.
Joel
On Wed, May 9, 2018 at 9:16 AM, Guru Shankara <gurushankara@xxxxxxxxxxx>
wrote:
Hi Experts,chassis.
I am working on a modem design that is powered by an AC/DC supply
(isolated).
The design includes a base board that hosts a mezzanine/daughter card
and both the baseboard and the mezzanine cards are powered by 12V DC.
The chassis walls and misc. mechanical hardware have a conductive
coating on the inside and will be connected to the
chassis/safety/earth ground of the AC/DC power supply.
As the name implies, the chassis/safety/earth ground provides for
safety of the operator if there is a situation where the higher
voltage side line of the AC/DC supply rips off and makes contact with
the
So, I prefer NOT to connect the board logic ground to the
chassis/safety/earth ground of the supply.
Any thoughts on if I should connect them together or not?
Also, if they need to be connected, is there a recommended method?
Really appreciate your help.
Thank you,
Gurushankar
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