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How to handle operational amplifiers if not used in multiple channels?

Latest Updated:03/01/2007

Question:

In a device with multiple channels, how should I handle the operational amplifiers not being used?

Answer:

The device will not be damaged if you leave the relevant input pins open, but the operation of the open channels will be unstable, which may destabilize the IC internallyNote. It is therefore recommended to make the input pins into voltage followers by connecting the + input to a potential within the common mode input voltage range (e.g. GND).



Note, however, that in the case of the uPC4556, the amplifier must have a gain of at least 10 fold.

Note [Example of instability]
  • When the input pin of an unused channel is left open, the channel becomes active due to noise application from an external source, causing the power supply current (of the unused channel) to fluctuate greatly. This fluctuation may affect the operation of the other channels in the same IC.


The unused pin processing method does not depend on the power supply method. A concrete example is described below.

[Concrete example]
Single power supply operational amplifier: The following power supply methods can be selected when using the uPC324.



Thus, even if the power supply method differs as illustrated above, process the unused pins with a voltage follower (as a recommended connection example). At this time, the + input pin must be set to a potential within the common mode input voltage range.

[Recommended connection example]


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Suitable Products
Operational Amplifiers
USB3.0 Host Controller
UPD720202
UPD720201
UPD720200A
UPD720200
USB2.0 Host Controller
UPD720102
UPD720101
UPD720100A