difference between SOP and DIP? Bad batch of chips?!

Discussion in 'General Electronics Chat' started by pgo1, May 3, 2016.

  1. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    Im currently transferring an existing design from through hole to surface mount. i got some boards back and made one up, and found the DAC (DAC0800LCM) was overheating. i looked over and over a the circuit and could see no mistake. The original works fine, this one is the layout. I removed the chip out and looked at what was on all the pins - they all looked fine. i measured the resistances between all the pins and ground / power rails blah blah. I eventually put the DAC in and bent all the input pins out so they didn't connect, but left all the rest in - hey presto! No overheating.

    I went through one by one and found the culprit - pin 7, input 3. I couldn't see anything untoward about this pin - no shorts on the soldering, no defects on the boards. I removed all connections so it was only connecting to the shift register which drives it - still overheating. This shift register drives all the input pins, so probably not an issue there... I disconnected the pin entirely and measured it to find something odd - it settles at the negative rail. none of the other input pins do this.

    i looked at the original design with the DIP DAC0800 - all the pins settle around 0. So then im thinking what the hell is going on - i changed the SOP DAC for a fresh one - same thing. And again - same thing. I put leads on the SOP package and put them in the DIP socket - same thing. So eventually after I just couldn't think of anything else i broke out the legs of the DIP package and put them on to the SOP pads - no overheating!!

    All my SOP DACs are overheating when I connect input 3! What the hell is going on? The datasheet lists no difference between the packages. Could this be a bad batch of chips? I've never had such a thing before! It's so bizarre, please somebody save me from pulling all my remaining hair out

    ***i actually mean SOIC, rather than SOP.... in case anyone is worried or it makes a difference***
     
    Last edited by a moderator: Oct 27, 2016
  2. crutschow

    Expert

    Mar 14, 2008
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    It sounds like you didn't notice that the pinout for the two packages is different(?).
     
  3. hp1729

    Well-Known Member

    Nov 23, 2015
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    On the SOP package the pinout is different from the DIP. Pin 7 is -V.
     
  4. OBW0549

    Well-Known Member

    Mar 2, 2015
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    On Page 1 of the datasheet: "Pin numbers represent the PDIP package. The SOIC package pin numbers differ from that of the PDIP package."
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Actually I don´t think there is any pin that is the same between the two packages.
     
  6. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    haha


    oh

    that explains that then. Remember to read *the whole* datasheet, kids

    thanks! Sanity restored
     
    Last edited by a moderator: Oct 27, 2016
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The difference between the two packages is that the SOIC pinout pattern is rotated four positions counter-clockwise WRT the DIP pattern. So if you solder 16 little wires to the SOIC part and tack them down to the rotated positions on the board, the circuit should work.

    ak
     
  8. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    nice tip. I wonder what the purpose of re-arranging the pins between packages is..
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    Probably the way the die is set into the package. Rotated 45 degrees off square in the DIP but there may not be enough room in the SOP. Just a guess.
     
  10. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    makes sense :)
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    It was tradition on DIP parts to put Vcc and GND at opposite corners of the chip. The placement of decoupling caps, with long leads, was problematical for some applications. Surface mount parts often have different pinouts to accommodate more efficient layouts on multi-layer boards.
     
  12. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    To mess with those that don't read the datasheet thoroughly :p
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    You need to fire the layout guy, or the layout checker.
     
  14. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    that would be me - it's a one man job. I would probably fire myself if I could
     
  15. Papabravo

    Expert

    Feb 24, 2006
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    I'm sorry for your pain, but at least you have a sense of humor. Maybe get a friend to lend a hand next time. I can't tell you how many times another pair of eyeballs has saved my bacon.
     
  16. pgo1

    Thread Starter New Member

    Nov 7, 2012
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    ahh it's fine really. I've not lost too much time and I've patched it up now

    true about the eyeballs, though. I wonder how long it would have taken me to notice on my own...
     
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