Benjamin said:
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
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.
