[sdiy] low input bias current opamps

Roman Sowa modular at go2.pl
Thu Aug 16 11:52:35 CEST 2018


I could give you possibly stupid answer that even JBT can be damaged by 
ESD, as I read about it in some report in the past. It only needs more 
charge. But Achim answered it nicely already, in more elaborate way, so 
I can only say amen to that.

Yes, it's seems so unlikely they all are damaged the same way. Maybe 
they're not what they seem to be? Counterfeit?

Roman

W dniu 2018-08-15 o 19:37, David G Dixon pisze:
> Thanks for the great response, Roman.
> Possibly stupid follow-up question:
> Why would ESD have an effect on a JFET-input opamp?  I thought that only 
> CMOS was susceptible to ESD, because of the oxide gate insulator, but 
> not JFET.  The LF444 should be no more susceptible to handling issues 
> than TL074.  The handling would have to have been unbelievably abusive 
> to damage the chips, I would have thought.
> If I'm wrong about this, please disabuse me!
> 
>     ------------------------------------------------------------------------
>     *From:* Roman [mailto:modular at go2.pl]
>     *Sent:* Wednesday, August 15, 2018 9:10 AM
>     *To:* David G Dixon; synth-diy at synth-diy.org
>     *Subject:* Odp: [sdiy] low input bias current opamps
> 
>     The answer to A) is no, because of 1)
>     Recently I made some THT design and was just so happy about it until
>     I found how many parts that I freely use in SMD are simply not made
>     in THT, so the choice usually comes to one part if any.
> 
>     The answer to B) is usually Mouser, but they have sometimes errors
>     in describing parameters, or take different values to the table,
>     like "typical" for one part and "minimum" for the other part.
>     Sometimes I use DigiKey, mostly because they seem to have more
>     refined parameters to search and I can type the quantity of
>     interest, and then sort by the price. Mouser sorts only at qty 1
>     which is useless.
>     And obviously all manufacturer's websites contain parametric search,
>     which is the most accuratre, but still I prefer Mouser because it
>     gives me guidance of the price and availability.
> 
>     And if it's for some S&H, why don't you stick with TL0xx? Are you
>     sure your switching key has lower leakage than bias of TL0xx opamp?
>     Or try LF347 maybe but it's inferior to LF444 in this application
>     anyway.
> 
>     Give LF444 a chance, get new ones, maybe they were handled very
>     badly and inputs were damaged by ESD because of bad storage. They
>     would still work but bias may be in range of nA instead of pA.
> 
>     Roman
> 
>     Dnia 15 sierpnia 2018 05:48 David G Dixon <dixon at mail.ubc.ca>
>     napisał(a):
> 
>         Hey Team,
> 
>         I'm looking for opamps with the following properties:
> 
>         1) Through-hole
>         2) Quad opamp
>         3) 14-DIP package
>         4) High power range (+/-18V, say)
>         5) Low input bias current (10 pA or less typical)
>         6) Pin-compatible with TL074, etc.
>         7) Not LF444 (cuz they all seem to be defective)
> 
>         So, basically, I'm looking for a suitable alternative for LF444.
> 
>         So, here are my questions:
> 
>         A) Do you know of such a thing
>         B) How does one go about finding such a thing, generally?
> 
>         Thanks in advance!
>         Dave (Floating VCA) Dixon
> 
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