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From: Daniel Haude
Subject: OPA627 - Is this proper?
Date: 30 Oct 2002 15:05:15 GMT
Organization: stoptrick: animated films
NNTP-Posting-Date: 30 Oct 2002 15:05:15 GMT
User-Agent: slrn/0.9.7.4 (Linux)
over the last years I've built a few preamplifier units utilizing the
OPA627BM part by Burr-Brown. In order to keep the opamp cool, I clamped
its TO casing into a metal bracket which in turn was screwed to the casing
(which is connected to ground).
This always worked fine. Now a colleague of mine tried to rebuild the unit
using an opamp from a newer batch. He managed to fry it. I told him how
expensive the damn things were. He took a new one. Fried it. I told him
again how expensive they were, adding an appropriate comment about his
competence (Unlike me, he'd been using all sorts of proper anti-static
precautions). Put the old part back in, all went fine.
He checked the data sheet. Found out that the Opamp casing was connected
to negative supply voltage. I concluded that he must have blown the
bonding wire from -Vs pin to chip/casing and suggested to connect -Vs to
the case (without mounting it to the grounded enclosure). Part worked
My question: I'm sure that when I built the first units years ago I made
sure that there wasn't supposed to be a connection between the case and
anything else. Wouldn't I? Anyway, the device worked fine for years and
still does (so it can't be that the case-ground connection was made only
recently by accident). Sadly I can't find the old datasheet from back then
So they must have changed the manufacturing process, changing some vital
electrical specs on the way.
My question: Is it common for such things to occur? Have similar things
happened to anybody else?
--Daniel (more curious than aggravated)
"The obvious mathematical breakthrough would be development of an easy
way to factor large prime numbers." -- Bill Gates, "The Road Ahead"
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