AW: [sdiy] Module input isolation?

[Czech Martin]

Depends on what you want. If precision performance is not crucial, a series
resistor of some kOhm
might do. I think this is mandatory to prevent latchup.
 
If you want to keep the input offset from wandering due to stress,
additional clamping diodes
might be a good idea. Comparators naturally work with high differential
input voltage, some designs
seem not to be too happy with this situation (surprising, if you think that
this is the normal application).
This would mean diodes to both supplies as well as between +  and - input.
Of course, any additional components introduce parasitics (capacitance,
junction capacitance, leakage).
It really depends on the application, on the chip and on the environment.
 
NS and AD have some good application notes, Bob Pease gives some good hints
in his book, as 
well.
 
 
m.c. (mars lander builder)
 
 -----Ursprüngliche Nachricht-----
Von: John Speth [mailto:JohnS at molectron.com]
Gesendet: Dienstag, 8. Januar 2002 18:33
An: Synth-DIY List (E-mail)
Betreff: [sdiy] Module input isolation?



Hi list! 

Is there any kind of isolation needed to protect silicon devices that serve
as inputs to the outside world? 

Let's say I have a synth module that uses an LM311 comparator.  And the
input to this module needs to go directly one of the LM311 input pins.  Does
this pin need any protection circuitry?  I'm afraid I'm not familiar with
any kind of bad stuff that might happen at that pin.

I'll probably hang a 1M resistor to ground to keep it from floating when not
connected. 

Thanks, John Speth 

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