Single ended driver...

Tak Asami asami at itc.adaptec.com
Thu Sep 19 11:18:15 PDT 1996


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Tak Asami <asami at itc.adaptec.com>
*
At the risk of embarrassing myself, allow me to bring out an ancient subject.
It's about the single ended driver.

I suppose most of us silicon vendors are working on dual mode (LVD-SE) 
driver by now, and due to the buffer bandwidth and high integration
requirements tasked to electronics, many of us are going to 3.3V technology.

Then suddenly it struck me that at 3.3V 10% supply voltage, it can be lower
than 3.0V at the driver power, and using N-N driver (which I assume all of
you are using today) it is next to impossible to meet 2.0V @7mA Voh 
requirement at that level.  You can kiss your active negation good bye.

But that's OK.  We'll go to P-N driver to avoid Vds drop. But wait, with
P-N driver, you really can't do hot-plug, because your P-ch device conducts
when the device power is off but SCSI bus is powered.

So I see a fairly generic problem whenever someone goes to 3.3V supply for
single ended driver.  And I am not yet talking about 7+V of transient 
voltage on SCSI bus which is potentially deadly for sub half micro process.

Did anyone ever look into this?  Hot plugging problem is not just for LVD
any more.

Tak Asami ================================================================
Adaptec Inc. / ITC
phone:  (714) 455-8202
fax:    (714) 455-8102
email:  asami at itc.adaptec.com
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