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IC unused inputs NOR gate

  1. Apr 25, 2016 #1
    I have a quad 2 input NOR gate ic in which I am only using two of the four gates. I have read on the internet that unused inputs must be tied to ground. But if I tie these inputs to ground then I would get a one on the output. Will that draw excessive current ?, should I tie them to Vcc instead so my output is zero ?
  2. jcsd
  3. Apr 25, 2016 #2


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    Staff: Mentor

    You can tie them either way -- the key is not to let any CMOS inputs float, since they can float to mid-rail, which draws excessive current in the input stage, and can make the output oscillate creating noise. Whether the (open) output pin is high or low doesn't affect the Idd current draw for the CMOS gate.
  4. Apr 25, 2016 #3


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    Science Advisor
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    To build on what Berkeman said a properly operating logic gate IC will draw current based on what is hooked to the output. So if you hook nothing to the output, you will draw the least current that is possible.
  5. Apr 25, 2016 #4
    Thanks guys
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