Re: Rework Schroff VME terminators to 3.3V

John B wrote:

On 24/02/2007 Joerg wrote:


Hello Folks,

We want to use a VME box that was meant for 5V VCC. The terminators
are the electronic plug-in style gizmos from Schroff (60800 series).
They have a L272M (power opamp) on there which per data*** doesn't
operate below 4V. We need to go to 3.3V. Has anyone found a quick and
easy mod for this?


I assume you're looking for 1.65V to drive the terminations. Couldn't
you add a small -3.3V bias supply for the negative rail, as most of the
current will be drawn from the +3.3V rail.


More like 2V bias since you typically want to stay a bit off the thresholds in case someone lets a bus line go for too long or doesn't have Schmitts. There won't be any negative supply other than the usual (weak) -12V rail. I'll probably need a L272 pin-compatible power opamp that can live with 3V.

--
Regards, Joerg

http://www.analogconsultants.com
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