At 04:38 PM 3/1/02 -0800, you wrote:
>What should I do with the unused pins on a dual CMOS op-amp (specifically,
>the National LM6482 rail-to-rail op amp)? If anything, is it enough to tie
>the inputs of the unused op amp together? Should they also be grounded?

The best thing to do in general is to connect the op-amp as a voltage-
follower (output to inverting input) and connect the non-inverting input to
ground if you have +/- supplies, or a voltage that the output can follow
to if you have a single supply. Next best thing is to ground the non-inverting
input with a single supply, and have output connected to inverting input.

Some op-amps do strange things when you go outside the common-mode range or
apply a high differential voltage. They can draw excessive input current
(Bipolar types sometimes have the equivalent of back-to-back diodes across
the input) or they can draw excessive supply current. Unfortunately they
often don't publish the schematics of the op-amps any more, so it's hard
to tell without actually testing. This one is a CMOS one, so it's immune to
some of the ills that affect bipolar rail-to-rail op-amps, but if you follow
the above ideas, you'll have more flexibility in dropping in alternative
op-amps if required.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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