Eeyore wrote:
m...@sushi.com wrote:
You might want to verify that the offset voltage won't be altered as
you put extreme differential voltage on the inputs. Generally, that is
why you put the protection diodes on the dif pair.
Well.... exactly.
The b-e junction will break down (avalanche) at about 6V reverse anyway so > what
happens when you apply say 12V differential to an unprotected input ?
Breakdown is kind of mushy. [The closer you look, the sooner you think
it broke down. This is because the physics are logarithmic, and you
are looking with linear eyes.] You can measure changes in the offset
at less that breakdown. Perhaps some localized part ot the junction
gets stressed. I just don't recall how significant this is, well, as I
always put in the diodes and only designed ASICs, where the op amp
specs are often not as important as opposed to designing an op amp for
op amp's sake.
Of course, with good instrumentation, you can
measure all sorts of small changes that may not be indicative of a
problem, .
I'm not really sure I'd get the warm and fuzzy feeling putting a
device on the market that whacked the unprotected dif pair. I suppose
it depends on the application.
