Am 20.05.2010 10:20, schrieb Invisible:

> Now looking at <http://focus.ti.com/lit/ug/scyd013b/scyd013b.pdf>, on
> page 231 (which is actually page 236 of the PDF file), we see that for
> the 74HC00 I'm looking at using, we have Icc <= 0.02 mA, Iol = -Ioh <= 4
> mA, and tPLH = tPHL <= 27 ns. Now, if I actually knew WTF that means...

 From the values specified there, I'm pretty sure Icc in this case means 
the maximum current that the IC will conduct from Vcc to GND under worst 
conditions.


As for Iol and Ioh, these are apparently the maximum currents that the 
IC can conduct from Vcc to output pins (in case of positive values), or 
from output pins to GND (in case of negative values), though I wouldn't 
be too sure whether these are...

(1.a) per-pin or (1.b) per-IC values;

(2.a) maximum values at which output voltage levels are still guaranteed 
to be within proper range, (2.b) absolute maximum values the chip is 
guaranteed to be able to supply, or (2.c) absolute maximum values the 
chip is guaranteed to survive.


tPLH and tPHL are probably signal propagation delays for low-to-high and 
high-to-low transitions, respectively.


I'd suggest you search <http://focus.ti.com/general/docs/dsnsuprt.tsp> 
for a product-specific datasheet, which will give much more detail, such as:


Absolute maximum ratings (i.e. values that, when exceeded, may cause 
permanent damage):

Continuous output current: +/- 25 mA
Continuous current through VCC or GND: +/- 50 mA


That is, for instance, if you plan to drive LEDs with 15 mA through one 
of these ICs, you /must not/ connect two in parallel to any output pin, 
and you /must not/ try to drive more than 3 LEDs in total per IC (unless 
you want to risk chip destriction).


Elextrical characteristics (i.e. values that are guaranteed by the 
manufacturer):

Voh (output voltage when pin is high) may (or may not!) drop as low as 
3.84 V (given a Vcc of 4.5 V) when sustaining a current of -4 mA (so I'd 
expect even lower values when trying to draw -15 mA)

Vol (output voltage when pin is low) may (or may not!) rise as high as 
0.33 V (again given a Vcc of 4.5 V) when sustaining a current of +4 mA 
(so I'd expect even higher values when trying to draw +15 mA)

That is, driving the LEDs in low-active configuration between Vcc and 
output pin is likely to give you a somwehat more predictable voltage.

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