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Absolute maximum voltage -- how long can digital chips stand it?

Discussion in 'Electronic Design' started by Bob Boblaw, Jan 2, 2013.

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  1. Bob Boblaw

    Bob Boblaw Guest

    How long do digital chips typically last when operated at their
    absolute maximum voltage?

    How long do they typically last at recommended voltage?
  2. mike

    mike Guest

    Are you sure you understand what you're asking?
    There's often a disclaimer in the spec that the device is not
    guaranteed to do anything at the absolute maximum voltage except survive.

    If you're suggesting that you will operate ANY component at its
    absolute maximum voltage, you should inform your employer so they
    can fire you before you put them out of business.
  3. Typically, no way to say
    Typically, 20 years?

    Tests I have made once on a 4000 series CMOS designed for abs max 18V failed at 21V. But that test was highly un-scientific


  4. Bob Boblaw

    Bob Boblaw Guest

    I don't want to run at that voltage. I'm just asking because
    others do, and I'm actually trying to talk them out of it.

    The chips are DDR3 DRAM recommended for 1.50V or 1.35V and
    rated 1.975V absolute maximum. A few retail brands of DDR3
    modules are sold with recommended voltages of 1.9V - 2.1V,
    those recommendations coming from the module marketers, not
    the chip makers, and I just want to know how long they'll
    likely last.
  5. Fred Bartoli

    Fred Bartoli Guest

    John Larkin a écrit :
    Any ref?
  6. Joerg

    Joerg Guest

    As a student I bought a few expensive Intersil chips for our RF
    institute. They were 5V nominal and something like 6V max. They would
    not work at all unless they saw at least 6.7V. Called them, was brushed
    off rather impolitely, they would not replace them. I never designed in
    an Intersil part in my whole career.
  7. Joerg

    Joerg Guest

    I like electronic parts to be more on the disciplined side :)

    Reminds me of an old friend. After a very long military career he
    started at an electronics company. Left after a few years. "So you
    didn't like the job?" ... "Oh, I did. I just could not stand civilians,
    with all their personality issues".
  8. Guest

    If it's MOS then the most likely failure mechanism is some kind of gate oxide overstress breakdown. Failures won't be measured in FITS then.
  9. miso

    miso Guest

    The answer is "indefinite." I always thought the absmax rating was kind
    of stupid since nobody specs the time it will survive. Parts with short
    circuit protect often have an indefinite time as well, though short
    circuit protection is on a better engineering footing that absmax. That
    is a design engineer understands the innards of short circuit
    protection, but there can be nuances in stressing devices.

    In the ATE characterization program (not to be confused with a test
    program), you typically stress a part for a second. Nobody is going to
    waste a second of test time for this in real life, i.e production.

    Some companies will run the characterization test under normal
    conditions, stress the part, then run it again to see if the numbers
    change. This is all different from company to company. I've yet to
    understand what all this ISO9xxx crap accomplished since quality flow is
    not standardized to the best of my knowledge. Or if it is, some
    companies go beyond the standard. The ISO standards make you document
    what you do, but don't specifically say what to do. [My opinion as
    someone who never worked in QA.]
  10. SoothSayer

    SoothSayer Guest

    One would think that the folks who would know would be the makers.

    The game overclockers do not always get it right, but I'll bet the
    makers have beat the hell out of them all.

    So, I'd ask Patriot or Corsair if an overclocked stick works better
    with the operating voltage tweaked, left alone or retarded. There are a
    number of other RAM 'firing' (reading, writing, refreshing) settings
    which can be managed on some motherboards as well.

    I think your points are valid, but when we are talking about mere
    tenths of volts here, I think the window indeed shifts, but the noise is
    nowhere around until one gets outrageous with the voltage tweak.
  11. miso

    miso Guest

    I don't have any experience with running RAM at maximum voltages.
    With increased supply voltage, you are fighting stronger "opposing"
    devices, so the threshold usually goes up, as in further from the rails.
    [The opposite sex device starts at the full supply voltage, so it is at
    full strength.] In any event, it is a bad idea to run at elevated voltages.

    DRAMs are quite sophisticated these days, employing PLLs and such. Some
    have thermal sensors. Why play with fire?

    Most of the intel mobos these days use 2x interleaved scheme. The older
    mobos were 3x. They made an "extreme" series that was 4x but the
    performance wasn't improved at all. In most cases, you are better off
    having more ram than less ram at a faster speed.
  12. Guest

    "Power dissipation goes up as the square of voltage" and "current goes
    up (somewhat)" is double-counting the increase. P~CfV^2.

  13. rickman

    rickman Guest

    I don't recall seeing any DRAM devices that weren't spec'd for Vdd of
    ±5%. Technically these devices were failing if your tester was accurate.

  14. rickman

    rickman Guest

    I've never been overly impressed with Intersil as a company. There is
    certainly no reason for rude support.

    I've worked places where getting a $5 PO through channels was a major
    PITA so I would ask for samples of nearly everything on the board. When
    I asked Intersil for a sample of a 4000 series CMOS part they responded
    that they don't sample those parts, they are well understood. I guess
    the effort on their part to sample the device was more than the effort
    on my part to get a PO though channels. So I didn't use the part. No
    big loss on either side.

    On the other hand, some sales folks understand the value of getting a
    part in the door at companies. Some companies make parts available in
    the schematic capture data base which can make things easier for
    engineers. This leads to those parts being designed in more often. So
    getting a part into a prototype can lead to sales even if that project
    doesn't use it in the end.

  15. rickman

    rickman Guest

    I've always wondered about that relationship, I seem to recall it is
    based on the Arrhenius equation. The basic Arrhenius equation has two
    arbitrary constants, one for the activation energy and one for the basic
    rate. The exponential describes how the rate varies with temperature.
    I find it odd when equations work out to nice round integers like 2:1
    and 10°C. That makes me think this is a vast simplification and is very
    approximate, mostly used because it is convenient and "close enough".

    Anyone know what the basis for this relationship is? I think I looked
    it up once and didn't find a real basis for it. There is no physical
    basis for 10°C so I expect it is all very arbitrary and actually varies
    a lot in the real world. Or is there something basic I am missing?

  16. rickman

    rickman Guest

    You are absolutely right. ISO9000 is more about being able to explain
    and justify what you are doing rather than making sure you are doing it
    right. There is lots of benefit in that. I was hired by one company
    who had hired more engineers in the past year than they had from prior
    to that. How do the new hires know how the company is to function? I
    don't recall if engineering was ISO9000, technically they were a DOD
    outfit and they were just getting their CMMI certification, which is
    much similar. In many ways CMMI training is a joke. The CMMI
    instructors know the "rules" for CMMI, but can't tell you anything about
    how to apply them to your process. In this case we all flailed about
    and did a lot of talking in circles. The worst part was in the first
    bid I worked on we were adding time to the schedule to make the CMMI
    stuff happen and it infuriated the head guy. "If it doesn't save us
    time and effort, why are we doing it?" That was a valid point so all
    the scheduled time for doing the CMMI stuff was removed along with a
    bunch of other fat.

    In many ways this company was using the infinite monkey process... but
    they did manage to get product out the door. Some of the factory people
    were pretty good, but some of them hated engineers. Too bad, I like
    working with manufacturing. No point in designing a product only to
    have it be hard to make.

  17. miso

    miso Guest

    The P=CfV^2 equation is based on shoveling buckets of charge at a given
    rate. But the shoot through aka crowbar current will go up with supply
    voltage. I'm reading Jeff's mind here, assuming that was what he meant.

    There is a lot more than just logic to RAM design. PLLs, sense amps
    etc,so the bucket of charge back of the envelope equation that works for
    basic logic might not be operable for a DRAM.
  18. Bob Boblaw

    Bob Boblaw Guest

    I don't think they test thoroughly but mostly use just PCs, and one
    company even admitted allowing up to 2 bad bits in final testing. Almost
    all retail modules are made with no-name or overclocked chips under their
    purely decorative heatsinks, like these 2133 MHz G.Skills containing
    Hynix H9 (1333 MHz) speed grade chips (pictures):

    10% of similar modules have failed on me, compared to 0% for modules
    made with brand name chips not overclocked.
  19. Guest

    Funny, I ordered three sticks of memory from Crucial (Micron) recently
    - one dead. I didn't think the 33% fallout, from the horse's mouth, to
    be very good either.
  20. Guest

    Shoot-thru looks like another capacitor; also proportional to f
    (number of transitions) and V^2 (impedance of the output devices).
    Also proportional to f and V^2. I don't see a V^3 component yet.
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