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Strength of CD4000 substrate diodes

Discussion in 'Electronic Design' started by Joerg, Dec 7, 2006.

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  1. Jim Thompson

    Jim Thompson Guest

    [snip]

    Well? It looks like you can "get away with it" ;-)

    Nevermind that, on a harvest moon, a cold damp night, an owl buzzes
    your head, and it blows all to hell ;-)

    Do it right!

    ...Jim Thompson
     
  2. Fred Bartoli

    Fred Bartoli Guest

    Jim Thompson a écrit :
    At least, if you can't make them change their mind about making it
    right, I'd ask them to sign that:
    * you don't advocate doing such a thing, but you've done it to their
    express request.
    * Then write that it's possible to anticipate (but not to guarantee) the
    behavior of parts through incoming sample testing *you* do (and be paid
    for) of *each* different lot, but since they insist on doing it wrong,
    you can't be held responsible for any consequences. Then maybe list some
    and put some estimated $figures.

    I've found this kind of *big* 'warning' enough to change even the most
    reluctant minds.
     
  3. Jim Thompson

    Jim Thompson Guest

    It's been a while, but I have done just that... "I won't sign off on
    it".

    ...Jim Thompson
     
  4. Joerg

    Joerg Guest

    Well, I opted not to push things this far. It'll be under 100uA now.
     
  5. Joerg

    Joerg Guest

    We can exclude all discontinued parts. The datasheets for part in
    production so far all seem to support 10mA. Which is actually quite good.

    With 74C you have to be really careful. I wouldn't ever drive any of
    these into the substrate diodes.
     
  6. Jim Thompson

    Jim Thompson Guest

    Great! I'm proud of you ;-)

    ...Jim Thompson
     
  7. John  Larkin

    John Larkin Guest


    Which reminds me of a circuit I designed recently:


    33 pF |\
    in-------||---------| >-----out
    |/

    tiny-logic
    gate


    which upset some people, but I left it in because it's so cool.

    John
     
  8. Jim Thompson

    Jim Thompson Guest

    Probably works for very large signals that are continuous... but I'm
    upset ;-)

    ...Jim Thompson
     
  9. Joerg

    Joerg Guest

    I can already hear the scoffing at the design review for the circuit I
    am doing right now.

    Did you ever use one of those blazingly fast inverters with feedback for
    an analog job?
     
  10. qrk

    qrk Guest

    Amazing, working with a 30+ year old logic family!
     
  11. Joerg

    Joerg Guest

    Yep. A Fairchild sales guy told me umpteen years ago that this series
    was doomed and to be obsoleted soon. Didn't believe him. Sure enough,
    then everyone even came out with SO packages. CD4000 is here to stay,
    for a long time.

    You can do amazing things with these. Plus you can run off batteries
    totally unregulated. That is a huge benefit when working on a design for
    a disposable. Same for very low power designs that must run off the
    mains rail.
     
  12. Joerg

    Joerg Guest

    Hello Mark,

    A little P.S.: I am using a 2N3904 in this new design. That ought to be
    as old as Methusaleh. But it worketh just fine!
     
  13. Jim Thompson

    Jim Thompson Guest

    Naaah! A 2N3904 is a "staple" ;-)

    Same with 2N3906.

    ...Jim Thompson
     
  14. John  Larkin

    John Larkin Guest


    No, is that what you're doing? Naughty boy.

    My favorite non-approved application lately is using insanely fast
    dirt-cheap LVDS-to-TTL receivers as comparators or as pin drivers, or
    both. At least, that's one I can talk about.

    We did find a really spiffy pin-fin heat sink we can epoxy to the top
    of one chip that we're using in a very unorthodox way, so if anybody
    does a less than exhaustive spy job, they'll think we have a custom
    asic.

    John
     
  15. Guest

    Most companies require 40ma latch-up as a bare minimum, but simple
    logic chips should be more latch-up resistant, say 80ma. Of course, it
    is really bad engineering to test such limits, and my numbers are room
    temp.
     
  16. qrk

    qrk Guest

    My 1972 Motorola data book has the 2N3904 in it. The modern data sheet
    has the same graphs as the old data book, even same layout order.

    Earlier this year I delivered a tiny board using 4000 series logic.
    Mighty fine logic series!
     
  17. Joerg

    Joerg Guest

    I'd probably still design some things with Ge transistors if the major
    mfgs would make them. When I was a kid I built all kinds of stuff with
    these. It was amazing to see a compressor amp still working on a single
    AA battery that already had begun leaking. Under 1V and it just wouldn't
    quit. Actually I was happily using it and only discovered the sub-1V
    condition because I saw something oozing onto the table.

    Absolutely. I wish that they would offer a device similar to the CD4007
    on the 74HC process.
     
  18. On Fri, 08 Dec 2006 08:15:16 -0800,
    John Larkin wrote
    I've done that, too, for a level translator. If the potential
    on the CMOS input "wanders off" it'll be clamped into range by
    the input diodes when the next transision occurs. Just keep
    that clock going!

    But it sure looks weird.

    robert
     
  19. John  Larkin

    John Larkin Guest

    Yeah. The input here is from 3.3 to 100 volts p-p. It varies from
    kilohertz at the high voltage to as much as 20 MHz on the low end.

    John
     
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