On "not connected" pins

Discussion in 'General Electronics Chat' started by Andrew1234, Nov 9, 2015.

  1. Andrew1234

    Thread Starter New Member

    Feb 16, 2015
    20
    1
    Hi
    I am using an op amp (AD8139), and one of the pins on the SOIC-8 package is listed on the datasheet as NC. The datasheet clarifies that this pin is not connected to the IC internally to the package.

    Should I literally not connect this pin to anything? Or is it safer for me to connect it to a fixed DC level, such as analog ground?

    Regards
    Andy
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Generally it makes no difference whether or not the pin is connected externally, but it's probably good practice just to connect it to ground.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,804
    1,237
    Historically, the convention held that 'NC' (not connected) meant there was no connection to the die -- whereas 'reserved' meant 'leave it alone' (i.e. floating) ostensibly to assure 'backward compatibility' of future versions (albeit there were a good many 'undocumented connections' bearing that designation -- the Z8000 CPU series comes to mind) --- Unfortunately the convention failed to become standard and all bets are off -- that said, I concur with @crutschow - either ground it of leave it untied but under no circumstances 'count on' the untied pin to be merely floating...

    Best regards
    HP
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    I vote float. If it's not a guzzinna or a guzzouta, don't touch it.

    ak
     
    eetech00 and RichardO like this.
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    +1 for letting "no connects" float. No connect should mean that the pin isn't internally connected. Contrast that with a "do not connect"; which, obviously, should not be connected:rolleyes:
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    The important word being should.

    ak
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Another vote for "no connection" being a direction rather that a description.

    If they say no connect then don't connect it.

    It could possibly have a function the Manu uses during their testing.
     
  8. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    It really doesn't matter, but I usually leave them floating. No need to tie it to a net.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Very occasionally in the past, a pin labelled NC has some production test function and NC ambiguously means "not connected", as in shouldn't be connected in any final application.

    Its quite rare and the data sheets are usually clear about that if its the case. Nonetheless, its a possibility that shouldn't be overlooked.

    If there's some particular danger of static buildup - maybe a 10M resistor to GND just to be on the safe side.
     
  10. eetech00

    Active Member

    Jun 8, 2013
    652
    112
    I vote don't connect...:)
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    That's probably the best way to go, but the data sheet should be carefully searched for any directions on the treatment of pins with no apparent function.

    With pins that go to an unused circuit block, there's usually a correct procedure. With logic it often as simple as tying high or low. With op amps, the simplest is tie the output back to inverting input, some op amps don't like saturated outputs, so it can be advisable to tie the non inverting input to some steady intermediate voltage level.
     
    eetech00 likes this.
Loading...