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How to deal with unused IC pins in pcb designs?

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tR|GG3rX

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unused pins

hi,

how to deal with unused IC pins in pcb designs. just leave it unconnected? will it affect other circuitries on the same pcb?
 

Re: unused pins

Search this forum for: unused AND pins
You will fnd a lot of ideas on this subject.

My practice is to leave them alone unless there is a reason to connect them to Vcc or GND.
 

Re: unused pins

The usual guidelines are:

Unused input pins: connect go ground
Unused output pins: leave them floating
 

Re: unused pins

Hi,
I agree with Andy here. It is important to prevent your inputs from floating.

It is dangerous to leave input pins floating, specially if you have multiple gates and a noisy board. You will get some difficult problems to solve when you start debugging your design.

BR,
/Farhad
 

Re: unused pins

farhada said:
Hi,
I agree with Andy here. It is important to prevent your inputs from floating.

It is dangerous to leave input pins floating, specially if you have multiple gates and a noisy board. You will get some difficult problems to solve when you start debugging your design.

And what about bi-directional pins? ;-)

It strongly depends on I/O ports schematic of target IC. Most of modern IC have internal weak pull-down (pull-up) on all pins, so you can easy leave them unconnected and simplify task for your PCB designer.

As to any particular IC - you have ALWAYS check with its datasheet/app.notes - there is no generic answer for this question.
 

unused pins

Yes,
That is true for a lot of ICs, but I normally connect them to the ground if they are not used, just to be safe!
And for the IOs, most of the time, I put a 10k pulup to the VCC, but in most of the designs I have been involved in, the board was for very complex devices or for hobby! In both cases, adding a few resistors or a couple of ground pins doesn't matter that much.

BR,
/Farhad
 

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