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From: Tony Williams
Subject: Re: OPA627 - Is this proper?
Date: Thu, 31 Oct 2002 08:58:46 +0000 (GMT)
NNTP-Posting-Date: Thu, 31 Oct 2002 09:04:34 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
Daniel Haude wrote:
> Says the 1994 Burr-Brown data book (I found one):
> "The case connection [...] may also be driven at guard
> potential to minimize any leakage which might occur
> from the input pins to the case. The case is not
> internally connected to -Vs."
> And the 2000 TI data sheet:
> "The case [...] is internally connected to the negative
> power supply as it is with most common op amps."
That looks like a serious and unwarranted spec change to me.
This is an opamp with 5pA max Ib, in a TO-99 case, with
glass-metal seals on all pins. Glass-metal seals do not
have much distance between the wire and the metal rim of
the seal. With a floating case you could actively drive
the metal rim for minimum effect on Ib. You now have a
situation where the metal rim of the seal is at -Vsupply.
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