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How should unused amplifier inputs be connected?

Latest Updated:03/01/2007

Question:

I will use a dual operational amplifier (uPC4560), but will not use one of the channels. I plan to connect the input pin of the unused channel to 0 V in V±= ±15 V, and leave the output pin open.
What kind of problems could occur with such a connection method?

Answer:

When using this connection method, in which the output is not returned to the input, the gain is extremely large. In this state, even small changes such as in input offset (VIO) can cause the output to swing sharply to the H level or L level. This VIO changes depending on changes in the operating ambient temperature (TA) (the VIO-TA characteristic curve of the uPC4560 is shown below). The fact that the output changes as a result of VIO intersecting 0 V is shown in the following figure. This output change could influence the channel that is used. Please consider using the recommended connection method (voltage follower) for the unused channel.

[VIO- TA characteristic]


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