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Is it OK to leave the unused inputs of general-purpose CMOS logic ICs open?

Unused CMOS inputs must always be connected to either Vcc or GND as shown below. Because CMOS has a very high input impedance, the output becomes unstable if any input is left open. Moreover, an open input could increase current consumption due to overlap current or cause an IC to malfunction.

Generally, current consumption and noise levels are not affected by how unused inputs are connected to Vcc or GND.

[Figure: Open input examples]

* An open Input is one of the causes of malfunctions, faults and device damage.

 

[Figure: Example of connecting unused CMOS inputs to Vcc or GND]

* Unused input pins must be connected to either Vcc or GND.

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