FreeLists / si-list / [SI-LIST] Re: Paralleling driver outputs - is this still done?

["Brown, Mike (Austin, TX)" <mibrown@xxxxxx>]

The old rationale for justifying this (drivers in the same package only) =
was "identical" PVT conditions and simultaneous (or nearly so) drive.  =
That would still hold, I think.  I haven't used it in years, mostly =
because I've had some control over the drive strength of the output =
circuits. =20

The conditions which allow the short to happen are not obviously =
different than the condition which permits "crowbar" current to flow =
from VDD to VSS when there is only one driver involved (assuming =
simultaneous drive).  The impedance of the package and board will serve =
to limit the magnitude of the current - for a few hundred ps, at least.

Your board test people are going to scream, unless you make provisions =
to enable one driver at a time for board test.

A maybe better way to drive multiple loads (assuming clocks or =
point-to-point topology) is a radial distribution of series terminated =
lines.  The Moto ap notes for their clock distribution PLLs covers this =
in pretty good detail.  That way, you don't have to tie the outputs =
together physically.

Let us know what you decide, and why, please.

Mike

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Grasso, Charles
Sent: Thursday, April 01, 2004 12:38 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Paralleling driver outputs - is this still done?


Greetings:
=20

I have a design that will (I believe) need to used a buffer for the =
clock.
The intent is to drive multiple loads from the driver. One concern is =
the
variable gate delays and the solution is to parallel the inputs and the
outputs.

=20

Is this technique still used ? Does anyone have a feel for the long term
reliability of the device driven is such a  way. The concern is that =
there
will be (for really short periods) a short between VCc and Gnd.

=20

Thanks..

=20

Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel:  303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Email: charles.grasso@xxxxxxxxxxxx; <mailto:charles.grasso@xxxxxxxxxxxx;
%20>  =20
Email Alternate: chasgrasso@xxxxxxxx <mailto:chasgrasso@xxxxxxxx>=20

=20

=20



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