Your scheme works until you realize a lot of peripherals such as cables, HBA
cards or drives have their logic ground tied to chassis ground by spec or by
design.
Chris Cheng
Distinguished Technologist , Electrical
Hewlett-Packard Enterprise Company
+1 510 344 4439/ Tel
chris.cheng@xxxxxxx / Email
4209 Technology Dr
Fremont, CA 94538
USA
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Christian D'Souza
Sent: Wednesday, May 9, 2018 10:22 AM
To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
Cc: joel@xxxxxxxxxx; gurushankara@xxxxxxxxxxx; si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Logic ground and chassis/safety ground
I agree with Lee's suggested method and have done so in the past with no issues.
Christian
On Wed, May 9, 2018 at 12:12 PM, <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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