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Re: Another op-amp stability question (LT1677)

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On 1 Apr 2017 16:46:00 -0700, Winfield Hill <hill@rowland.harvard.edu>
wrote:

>John Miles, KE5FX wrote...
>>
>>On Saturday, April 1, 2017 at 9:16:52 AM UTC-7, tabb...@gmail.com wrote:
>>> It's a known issue with some opamps, but I've stayed quiet cos I can't 
>>> remember where a datasheet (IIRC) talks about it. IIRC the advise was 
>>> to keep source impedance under 10k, and the cause is stray capacitive 
>>> coupling from output to input plus a faster input stage than output 
>>> stage. But as I say, I can't remember where this was from so ICBW.
>>
>>Doesn't seem like a typical phase-margin gotcha, or one that involves external
>>coupling or feedback of any kind.  There's no sensitivity to stray C at 
>>all.  There must be a thermal component to the phenomenon, because it's only
>>noticeable at very low frequencies and is quite sensitive to temperature.  The
>>oscillation itself is around 700 - 800 kHz but I've never seen it appear on
>>signals above a few kHz.  No electrical time constants are anywhere near that.
>>
>>Given that people don't usually use pricy low-noise opamps with high-
>>resistance sources, I guess it's not too surprising that the issue isn't
>>well-known.  That's no excuse for manufacturers not knowing about it and
>>warning accordingly, though.
>
> Yes, John.  But I think its safe to say opamps going through
> input-pair transitions at certain voltages are suspect to be
> used at those voltages.  Your experience illustrates that point.

But what's the use of a rail-to-rail opamp if, well, you can't use it
rail to rail? I mean, really!

Sounds like LTC scrooed up that one.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 00:37 -0700
  Another op-amp stability question (LT1677) pcdhobbs@gmail.com - 2017-03-29 04:50 -0700
    Re: Another op-amp stability question (LT1677) piglet <erichpwagner@hotmail.com> - 2017-03-29 13:23 +0100
    Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 10:58 -0700
      Re: Another op-amp stability question (LT1677) tabbypurr@gmail.com - 2017-03-29 11:15 -0700
      Re: Another op-amp stability question (LT1677) Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2017-03-29 23:29 +0200
        Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 17:14 -0700
          Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 18:06 -0700
          Re: Another op-amp stability question (LT1677) Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2017-03-31 14:40 +0200
            Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-31 14:49 -0700
              Re: Another op-amp stability question (LT1677) Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-31 20:39 -0400
              Re: Another op-amp stability question (LT1677) tabbypurr@gmail.com - 2017-04-01 09:16 -0700
                Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-04-01 15:03 -0700
                Re: Another op-amp stability question (LT1677) Winfield Hill <hill@rowland.harvard.edu> - 2017-04-01 16:46 -0700
                Re: Another op-amp stability question (LT1677) John Larkin <jjlarkin@highlandtechnology.com> - 2017-04-01 17:31 -0700
                Re: Another op-amp stability question (LT1677) tabbypurr@gmail.com - 2017-04-01 20:59 -0700
                Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-04-01 21:41 -0700
                Re: Another op-amp stability question (LT1677) tabbypurr@gmail.com - 2017-04-02 04:53 -0700
                Re: Another op-amp stability question (LT1677) John S <Sophi.2@invalid.org> - 2017-04-02 16:26 -0500
                Re: Another op-amp stability question (LT1677) krw@notreal.com - 2017-04-02 19:29 -0400
                Re: Another op-amp stability question (LT1677) John S <Sophi.2@invalid.org> - 2017-04-02 18:34 -0500
  Re: Another op-amp stability question (LT1677) John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-29 05:18 -0700
    Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 10:56 -0700
      Re: Another op-amp stability question (LT1677) John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-29 13:02 -0700
        Re: Another op-amp stability question (LT1677) "John Miles, KE5FX" <jmiles@gmail.com> - 2017-03-29 17:57 -0700
          Re: Another op-amp stability question (LT1677) John S <Sophi.2@invalid.org> - 2017-04-02 16:31 -0500
      Re: Another op-amp stability question (LT1677) John Larkin <jjlarkin@highlandtechnology.com> - 2017-04-15 08:58 -0700

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