[SI-LIST] Re: About the chassis gnd and logic gnd

Peter, ESD.  It may change where a spark is likely to strike.
Regards,

Steve.
At 11:29 AM 3/26/2004 +0800, peter zhu wrote:
>Steve:
>
>There might be some issues if this is a midplane or you are plugging in 
>transceivers to the outside world.
>why?
>
>peter
>----- Original Message -----
>From: steve weir
>To: peter zhu ; si-list@xxxxxxxxxxxxx
>Sent: Friday, March 26, 2004 10:39 AM
>Subject: Re: [SI-LIST] About the chassis gnd and logic gnd
>
>
>Peter, my best recommendation is frequent ties between logic and shelf 
>ground.  Keep the -48V return fully isolated from logic and earth within 
>each chassis.  The -48V return should tie back to earth at the customer 
>battery plant / power supply.
>
>Your backplane attachment sounds OK, at least superficially.  There might 
>be some issues if this is a midplane or you are plugging in transceivers 
>to the outside world.
>
>Are you developing that in China or CA?  If there is someone in Alameda 
>involved we could set up an hour or two consulting session to review the 
>plans.
>
>Regards,
>
>
>Steve.
>At 10:25 AM 3/26/2004 +0800, peter zhu wrote:
>
>Steve:
>
>We are developping ATCA chassis and using isolated DC-DC converters.
>In fact, In ATCA chassis, there are three gnd: shelf gnd, -48v Return, and 
>logic ground. Now I plan to tie the shelf gnd and logic gnd on backpalne, 
>and let the -48V Return separated. The 48V Return may tie to shelf gnd on 
>shelf using single point.
>
>On backpalne PCB, we only use one gnd stack, all logic gnd and shelf gnd 
>from connector pins are connected to this gnd stack. if the screw that fix 
>the backpalne on the margin are installed, the gnd stack will be connected 
>to shelf. do you think this is feasible?
>
>Thanks!
>
>Peter
>----- Original Message -----
>From: steve weir
>To: peter.zhu@xxxxxxxxxx ; si-list@xxxxxxxxxxxxx
>Sent: Thursday, March 25, 2004 11:52 PM
>Subject: Re: [SI-LIST] About the chassis gnd and logic gnd
>
>
>Peter, the subject has been covered many times.  There are seemingly 
>religious views on this.
>
>
>I belong to the "reduce antenna gain" camp, which is to say that at high 
>frequencies, even an air gap does not effect isolation, it just increases 
>antenna gain and ESD susceptibility.  So multipoint bonding is the 
>preferred strategy in my book.  Bond often, and bond well.  There is one 
>caveat, and that is if you have external low voltage power supplies, then 
>you have to watch the return current path.  But since you likely use 
>isolated DC-DC converters, this should not present an issue to you.
>
>
>This point of view is supported by practices at major successful 
>manufacturers such as Cisco where those practices resulted in behemoth 
>boxes like the 12000 that have no EMC issues at all.  It is also supported 
>by respected authors like Mark Montrose, and Doug Smith who show the 
>science behind why this practice works, as well as successful engineers 
>with many years experience like Chris Cheng.  My recollection is that John 
>Barnes covers this subject in his books as well.  If you can afford them, 
>and even if you can't, John brings many years experience including with 
>ultra cost sensitive consumer product.
>
>
>If you go to Doug Smith's web site, www.emcesd.com and look up his April 
>2002, May 2002, and October 2002 "Technical Tidbits" he demonstrates the 
>value of multipoint grounding very clearly for ESD immunity.
>
>
>Regards,
>
>
>
>
>Steve.
>At 07:43 PM 3/25/2004 +0800, peter zhu wrote:
>all:
>About the chassis GND and the logic GND, some company tie them together, and
>some sompanies separate them.
>In telecom equipments, I see many companies, such as NOKIA, tie them
>together, and the backplane only has uniform GND layer for chassis gnd and
>logic gnd. We separate them in our backplane, but it will result in PCB gnd
>layer partition. So form the PCB view, we hope the uniform gnd.
>What's the recommendation form the EMC/EMI view? and what's your company's
>strategy?
>
>
>Thank,
>
>
>Peter
>UTStarcom
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>
>or to administer your membership from a web page, go to:
>http://www.freelists.org/webpage/si-list
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
>List FAQ wiki page is located at:
>                 http://si-list.org/wiki/wiki.pl
>
>
>List technical documents are available at:
>                 http://www.si-list.org
>
>
>List archives are viewable at:
>                 http://www.freelists.org/archives/si-list
>or at our remote archives:
>                 http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
>                 http://www.qsl.net/wb6tpu
>
>Steve Weir
>Teraspeed Consulting Group LLC
>2926 SE Yamhill St.
>Portland, OR 97214
>(503) 239-5536
>http://www.teraspeed.com
>------------------------------------------------------------------------------------------------------
> 
>
>Teraspeed(SM) is the service mark of Teraspeed Consulting Group LLC
>Steve Weir
>Teraspeed Consulting Group LLC
>2926 SE Yamhill St.
>Portland, OR 97214
>(503) 239-5536
>http://www.teraspeed.com
>------------------------------------------------------------------------------------------------------
>Teraspeed(SM) is the service mark of Teraspeed Consulting Group LLC

Steve Weir
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
------------------------------------------------------------------------------------------------------
Teraspeed(SM) is the service mark of Teraspeed Consulting Group LLC


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: