[SI-LIST] Re: Crowbar current in push-pull drivers

It depends on who designed the driver. I have seen designs that
bootstrap the input to the output transistors and it creates this high
crowbar current you are seeing. It is kind of like adding pre-emphasis
in a crude way.

I have also seen designs that do not
do this and the crowbar current is less, but still greater than
8mA for an HSTL Class I device.

Depends on the bandwidth you want out of the buffer and the media
you are going to drive. Since we are driving nothing more than
a circuit board, we have opted for a slower, less robust design.

Jonathan, tell Barry Gilbert and Dan Schwabb I said hi.

Regrads,
Bob Kezer

-----Original Message-----
From: Fasig, Jonathan L. [mailto:fasig.jonathan@xxxxxxxx]
Sent: Friday, August 29, 2003 11:51 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Crowbar current in push-pull drivers


Does anybody have a feel for how much crowbar current 
(aka shoot-thru current) one should expect to see from a 
"well-behaved" HSTL-Class-1 or SSTL-18 driver? I am seeing 
43ma and 23ma transients (respectively, per driver) on the 
I/O supply when my drivers are switching.  These transients 
are two hundred to three hundred picoseconds in duration.  
Are these switching transients typical?

---------------------------------------------------------------

Jonathan Fasig                  Email:  fasig.jonathan@xxxxxxxx 
Mayo Foundation 
4001 41st Street NW 
MSC Sn 2-132                    Phone:  (507) 538-5464
Rochester, MN 55901             Fax:    (507) 284-9171



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