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Don't connect vs no connect

Discussion in 'General Electronics Discussion' started by Braeden Hamson, May 4, 2018.

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  1. Braeden Hamson

    Braeden Hamson

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    Feb 18, 2016
    I came across an IC that had pins labeled no connect and don't connect. This was on the same IC. What's the difference and what should I do with each?
     
  2. Minder

    Minder

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    Apr 24, 2015
    NO connect = no internal connection
    DO NOT connect = do not connect to pin.
    What is the IC No.?
    M.
     
  3. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Under some circumstances the 'no connect' pin can be used to take a 'via' through a pcb whereas the 'do not connect' pin can't (since it has some internal, but unused, signal on it).
     
    Braeden Hamson likes this.
  4. Braeden Hamson

    Braeden Hamson

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    Feb 18, 2016
    Ahh, that is a very important distinction.

    Another quick question, would you consider it "good practice" to use the NC pins as vias?
     
  5. Braeden Hamson

    Braeden Hamson

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    Feb 18, 2016
    My professor was showing us a datasheet in class. Unfortunately I don't remember the part number. Although it was a OTP EPROM (So much contradiction in that name hahaha)
     
  6. kellys_eye

    kellys_eye

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    For the 'mega pin' devices (like ball-grid-array (BGA) processors) the use of spare (NC pins) can be very useful - but as you get down in pin count it becomes rare to have to use them for such a purpose given the track width and ease of placement of a via.

    I have seen pcb's that utilise the NC pins on DIP devices - either as a via or simply to avoid running tracks between pins - but it isn't that common a practise in my knowledge.
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I recommend not connecting NC pins at all.
    Using NC pins in your layout may prove fatal later if you need to replace the original chip for whatever reason by a compatible chip. A compatible chip (new revision by same manufacturer or model by another manufacturer) may make use of that NC pin(s). This use of the former NC pin is likely not compatible with your layout.
    If this is a one off project then these considerations are moot, of course.

    Why would a compatible chip use a pin that is NC one the original model? One reason my be, just for example, that another manufacturer uses the original NC pin to trim the circuit on the chip to improve performance over the original chip. Or to add functionality, e.g.monitoring an internal circuit point etc. etc.
     
    Braeden Hamson likes this.
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