Walter,
Tom beat me with an answer, so he is the winner of the lunch again,
but in the days when the 3.3V devices started to come out and they
were frequently used together with 5V devices, they started making
them "5V safe". In practice this meant that the pullup transistor's
parasitic diode had to be connected to a higher voltage than its
normal 3.3V pullup supply so that the diode would not clamp the 5V
high level signal to about 3.3 + 0.6 = 3.9V. If this clamping would
have been allowed to happen, the 5V pullup would have driven a lot
of current through the 3.3V clamping diodes... So in those days there
were a ton of 3.3V devices which had a 5V supply for the clamping
diodes of their pullup transistors. I don't think it would be too
hard to find such devices even today.
Thanks,
Arpad
======================================================================
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] ;
On Behalf Of Walter Katz
Sent: Sunday, March 13, 2016 12:00 PM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] The next I/O Buffer Challenge
All,
Congratulations to Tom Dagostino for winning the last I/O buffer challenge and
for receiving the challenge award of a lunch at a restaurant in Portland.
The next challenge is to find a real buffer that has more than two rail
voltages. Specifically a non-ECL buffer that either:
[Pullup Reference] is not equal to [Power Clamp Reference]
Or
[Pulldown Reference] is not equal to [GND Clamp Reference]
Or for an ECL buffer that
[POWER Clamp Reference], [Pullup Reference] and [Pulldown Reference] are not
equal.
In order to win the challenge (and a free lunch) you must be the first person
to supply a link to a data sheet for a commercially available part that
requires more than two rail voltages for an IBIS buffer.
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
