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terminating unused parts of multichannel opamps
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Old 2nd June 2004, 11:26 PM   #1
matjans is offline matjans  Netherlands
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Default terminating unused parts of multichannel opamps

hey guys,

i'm designing an active filter with a couple of quad opamps of which i only need 3 amps per ic. One of the opamps (per ic) is unused. After reading the 'opamps for everybody' chapter 17 i have a questions.

At the bottom of page 29 there is a paragraph on how to correctly terminate unused parts of opamps. In the drawings they mention 'half supply'. I'm guessing that when using +/0/- rails the half supply == 0 or ground. Am i correct?

Second question; what does 'open' or 'zero' mean in the rightmost picture at the top of page 30?

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Old 2nd June 2004, 11:39 PM   #2
peranders is offline peranders  Sweden
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terminating unused parts of multichannel opamps
You should always tie unused opamps to something.

Some opamps can be tied to negative supply but check datasheet first, like the LM324 and any rail-to-rail opamp.

If you have a dual supply must connect the opamp as voltage follower (inverting input to output) and the non-inverting input to ground or to some potential within the common mode limits.

Why you should do it? To minimize the influence of the unused opamp to the ones wich are in use.

Zero = connect
Open = do not connect

but seriously I think they ment that ZERO some resistance, like 1 kohms or so.
/Per-Anders (my first name) or P-A as my friends call me.
My group buys Super Regulator group buy. 48 pcb's in order, 44 paid, 2 left to order.
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