RE: [SI-LIST] : Connector pin pwr/gnd ratio

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From: Jeff Zheng (jzheng@photobit.com)
Date: Mon Nov 13 2000 - 14:35:15 PST


First, I would check what's the maximum current on 3.3v and 2.5v that
pass thru the connector, and what's the max. current each pin can
handle from the connector spec. make sure I have enough pins to
handle the current load (probably 50-100% more.) use at least same
amount of ground pins for each power return.

Second, distribution. Molex application note gives some suggestions
on ground/signal pin assignment patterns based on signals are single-
ended or differential. Of course, the ground pins distribution
becomes critical only if a lot of hi speed signals in this connector.

Jeff

On 13 Nov 00, at 16:43, Peterson, James F (FL51) wrote:

> The original question was meant to be:
>
> On my board (CMOS logic), I have 85 connector pins allotted for 3.3v,
> 2.5v and gnd. How would you distribute? and why?
>
> Would you do 25% for 3.3v, 25% for 2.5v, and 50% for gnd? (which is a
> component approach, but maybe not a board approach.)
>
> Would you minimize the pwr pins and maximize the gnd pins? if so, why?
> (don't we have return currents flowing in both.)
>
> all inputs and opinions are welcome and appreciated.
>
> Jim
>
>
> -----Original Message-----
> From: Charles Grasso [mailto:chasgra@msn.com]
> Sent: Monday, November 13, 2000 4:25 PM
> To: Peterson, James F (FL51); si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Connector pin pwr/gnd ratio
>
>
> The allocation of grounds with respect to any number of signals is
> mainly based on rise time (hence frequency content). That is to say
> the faster the rise time the more grounds you need - the asymptote
> being a solid "bar" connection found in many impedace controlled
> connectors.
>
> ----- Original Message -----
> From: "Peterson, James F (FL51)" <james.f.peterson@honeywell.com> To:
> <si-list@silab.eng.sun.com> Sent: Monday, November 13, 2000 6:57 AM
> Subject: [SI-LIST] : Connector pin pwr/gnd ratio
>
>
> > Hello,
> >
> > I'm looking for some information on what the pwr/gnd ratio should be
> > for a board's connector. (I know there is something in the archives,
> > but I couldn't find it.)
> >
> > Someone said a rule of thumb is a 3 to 1 ratio, but I'm not sure
> > what that is based on.
> >
> > So let's say for example I have 85 connector pins for 3.3v, 2.5v and
> > gnd. How would you distribute? and why?
> >
> > thanks
> > Jim
> > > Jim Peterson
> > > james.f.peterson@honeywell.com
> > > Honeywell Space Systems
> > > M/S 934-5
> > > 13350 U.S. Hwy 19 N.
> > > Clearwater FL, 33764-7290
> > > Office : 727-539-2719
> > > Fax : 727-539-2183
> >
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>
>
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