[SI-LIST] Re: HIGH DC Current on GND Plane

  • From: istvan novak <Istvan.Novak@xxxxxxx>
  • To: joepaulm@xxxxxxxxx
  • Date: Tue, 19 Jun 2007 07:00:11 -0400

Hi Joe,

There are the following generic guidelines that come to my mind, not 
knowing the
details of the system:
- if the 60A power rail serves also as reference for SerDes lines, it 
has to be quited sufficiently
for that purpose, which means that you need to design that rail as a 
high-speed power rail.
This is especially true if you also need to carry reference clock or 
sensitive low-level analog
signals around the backplane. 
- if you have switching regulators connected to this rail (most probably 
you have), either
feeding this rail with raw power or taking this voltage to generate 
local sypply voltages,
you want to check very carefully for high-frequency ringing generated by 
the converters.
Today the ringing can be anywhere in the 50-500MHz frequency range; if 
they spread
freely on the power rail, it will reduce your SerDes margin.  
Unfortunately the ringing
is not limited by converter specifications (in other words there is no 
spec item for the
potential high-frequency ringing).
- as others pointed out, you dont need to worry about saturation of 
copper, unless you
have local features increasing the current density too much.  Make sure 
you use the
largest area that you can afford and many vias for connecting the 
high-current inputs
and outputs.

Regards,

Istvan Novak
SUN Microsystems

Joe Paul M wrote:

>I have a midplane carrying 60Amps of current and Same GND plane is used 
>as reference for multiple of 6.6 Ghz serdes lines , PCI-e lines and GE lines
>Is there anything similar to 'saturation' in Inductors applicable to GND 
>plane?
>( Due to saturation of flux in the flux carrying medium , beyond a 
>certain amount of DC current inductors saturate and wont act as 
>inductors for any AC superimposed on the DC. )
>Will cross talk increase due to the absence of mutual inductance between 
>signals and gnd plane ?
>Is there anything else that can go wrong due to this DC , AC current 
>mixing in planes ??
>
>
>
>
>
>
>
>  
>

------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list

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


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

List archives are viewable at:     
                //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: