I'm looking at the datasheet for the 74LS193 binary counter and typical "HI"
output voltage is 3.4 volts but the current is listed as a minus 0.4 mA
How can you have a plus voltage with a minus current?
I also see this confusion on the 74LS08 AND gate chip.
I'm sure this confusion stems from my inexperience and hopefully someone can
explain this to me.
Thanks in advance,
Bart
The minus sign merely indicates direction. Note that the max LO current is
+8.0mA. When dealing with digital TTL circuits, you'll run into the terms
"source current" and "sink current." The logic "1" output is typically the
"source" state, and indicates that the TTL device must be the source of the
current for the node, and the value of 400uA is the max that the gate
output node can be expected to deliver. When the device is switched to
"0," it can be used as a "ground" or "return" "sink" for a separate source
of current somewhere on the node, and the max value is the maximum current
that the gate can be expected to pass when so configured. I hope that you
can see from this explanation that the current direction will be opposite
for each case.
Again, the sign only indicates a direction, and I'm not sure why the data
sheets determined which direction should be "-" and which should not.
That, at least, is my basic understanding of it. If I've erred on some
small point, Phil Allison, our resident keeper of all things CORRECT AND
PROPER, will be along shortly to call me a twit and a retard, and fail to
help in any way toward correcting the error.
HTH!