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74LS04 TTL interter

Discussion in 'Electronic Basics' started by Benjamin Gearhart, Sep 10, 2003.

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  1. Okay, my first question of probably way too many coming soon, lol.
    I know the Vcc of the 74LS04 is 5 volts, and 5.25 volts maximum recommended.
    (I see that the NS-military version- is 5.5 volts max recommended, just odd
    to me that the commercial standard had higher standars that the military
    one..hmmmm)
    I'm going to apply an input waveform to the abovementioned inverter, my
    question is, what are the max positive and negative peak voltages that I
    should apply? Wouldn't they just be 5.25 max?
    (dumb me doesn't have a databook cause all are sold out, would that info be
    in there anyway, or is this just a common sense question?)

    Thanks in advance!:)
    -Ben
     
  2. The military are guaranteed over a wider range of temperatures than
    the commercial ones are. I suspect the military have required chips
    that work over a larger supply range, also. The manufacturers charge
    a very large premium for those wide range selected units.

    Almost all logic chips in the TTL and CMOS families work fine with
    inputs that vary between the supply rail voltages. TTL chips go
    through their logic swing as the input voltage pass through about 1.5
    volts above the negative rail voltage, so it is not so important that
    the input swing all the way to the positive rail. Any input above
    about 2 volts definitely a log high input and is as good as any other
    voltage between that and the positive supply rail at keeping the
    output low. Any input below .8 volts above the negative rail is a
    definite logic low.

    If you want a gate that squares up an analog voltage, LSTTL may not be
    the best family, since they draw continuous input current when the
    input is a logic low. CMOS logic has a very high input resistance
    (essentially a capacitor) so it is very handy when working with analog
    inputs. There is a 4000 series like the CD4069 that has a supply
    range from 3 to 18 volts. There is a high output current version, the
    CD4049, and some schmitt trigger versions that switch at two levels,
    one going up and a lower one going down, to prevent the output from
    hovering between logic levels. An example would be CD40106.

    There are several other CMOS families. The 74HCxx family is faster
    than the 4000 series, but has a smaller supply range (2 to 6 volts)
    with the logic threshold essentially at the half way voltage. The
    74HCTxx family has the same speed and supply range as the 74HC family,
    but has input threshold similar to the LS family, and the ability to
    pull down with enough current to drive some LS gates (remember that
    input current?). Any family that starts with the number 74 have
    pinouts and active states that match the same suffix number 74LS
    parts.

    There are also even faster families and ones with much faster speed,
    but these should get you started.
     
  3. John Jardine

    John Jardine Guest

    To download datasheets for *any* device just try typing the number
    (eg"74LS04") into Google and look at the first few links.
    regards
    john
     
  4. You're looking at it backwards. The commercial part requires *tighter*
    tolerances (5%) on the power supply, not looser (mil spec 10%).
    As others have said, anything below .8C (but not below -.6v or so) and
    anything above 2.0 (not to exceed Vcc+.6V) should work fine.
    Look on the net. These datasheets are out there. A *quick* search
    reveals: http://focus.ti.com/lit/ds/symlink/sn74ls04.pdf
     
  5. jibaro

    jibaro Guest

    Military hardening. the part is less susceptible to damage by a simple
    failure elsewhere in the circuit. the system still works albeit in degraded
    mode.
    there is a time and a place for higher standards....
     
  6. You know, this is a pretty interesting misconception. Most "military" parts
    are simply screened to operate at the military temperature range and any other
    spec that gets thrown at them. Typically, they are not "hardened" so to speak.
    They just come from the same batch of wafers and get tested to -55C / +125C and
    then make sure they meet propagation delay plus perhaps a couple of other simple
    specs. Those that fall out are then screened to -35C / +85C or some other
    similar range and are graded as "industrial". The rest simply have to operate
    at some much milder temperature range like 0C to 70C and still operate well.
    Those are commercial parts.
    The temperatures ranges may change a bit from vendor to vendor (for
    instance, National Semiconductor would typically be -55C to +125C for
    military, -40C to +85C for industrial, and 0C to +70C for commercial), but the
    bottom line is - they are all the same devices.
    Note that the speed figures and propagation delay figures for commercial
    parts were usually the best. Well, yeah, but typically the others would run
    that fast too- just not across the whole temperature range. So you see
    derating, not hardening.

    Cheers!

    Chip Shults
    My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
     
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