Connect with us

unused pins on 4093 IC- what to do with them?

Discussion in 'Electronic Design' started by Will Waterston, Feb 19, 2007.

Scroll to continue with content
  1. I am building a small circuit that uses this 4093 ic, but I am only using
    pins 1-7 and pin 14 of course for power. Pins 8-13 are not being used.
    What should I do with these pins? Since I am using a socket, I was going to
    just clip these pins so they wouldn't be part of the circuit board and just
    solder in pins 1-7 and 14, but now I'm coming across readings that there
    should be no pins left open with this IC since it is CMOS. Can I leave
    these pins open and, if not, should I just ground them or pull them to
    ground with a 3-5K resistor?

    Thanks in advance,
    Will
     
  2. mkaras

    mkaras Guest


    Unused logic inputs to CMOS chips should generally not be left open.
    (The only case where it is ok is in those where the manufacturer has
    designed in some on-chip pullup or pulldown scheme). In the case of
    this part the inputs to your spare gates should be tied to a
    legitimate logic high or logic low level. For simplicity on a hobby
    type project it would be suitable to simply ground pins 8 & 9 and also
    12 & 13. Do not ground pins 10 and 11 since these are outputs and part
    damage could occur if you did so.

    For the inputs you could actually do any of:
    - ground as suggested
    - pull down to ground via a resistor
    - tie direct to VDD (same rail as pin 14)
    - pullup to VDD through a resistor
    - tie the pins to some other logic device output that is at a known
    idle level as a high or low.

    - mkaras
     
  3. Tim Wescott

    Tim Wescott Guest

    On a production board it is often wise to pull the inputs up or down
    through resistors. That way if you need a spare gate you'll be able to
    get to it without lifting pins -- I always try to design my boards to
    make greenwire mods easy.

    If you're _really_ paranoid you'll bring the spare outputs out to vias
    or pads, to have them available, too.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-