IC unused inputs NOR gate

  • #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 ?
 

Answers and Replies

  • #2
berkeman
Mentor
59,009
9,104
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 ?
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.
 
  • #3
Averagesupernova
Science Advisor
Gold Member
3,788
733
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.
 
  • #4
Thanks guys
 

Related Threads on IC unused inputs NOR gate

  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
4
Views
19K
Replies
5
Views
400
  • Last Post
Replies
14
Views
8K
Replies
5
Views
1K
  • Last Post
Replies
3
Views
340
Replies
29
Views
3K
Replies
2
Views
83K
Replies
1
Views
2K
Top