[time-nuts] Performance of 74LVC series ICs

Bob Camp kb8tq at n1k.org
Sun May 31 16:59:30 EDT 2015


Hi

The 74HC series is an “old and slow” CMOS family. In some cases people use
their low speed to do filtering (they won’t follow a fast glitch …). Other than that
sort of thing, the AC and LVC should be fine replacements for them. The HC
might pull a little less power with nothing going on. If you are running on a coin 
cell it’s worth checking. 

The 74AC series was essentially the first group of fast CMOS parts to hit the market.
They were indeed fast. They also had some issues with lead frame induced glitches 
(power and ground pin locations …). You see a lot of odd things done to try to take
care of this. 

Starting about 20 years ago, people began to bring out “improved” versions of the AC 
parts. Processes had gotten faster and people had learned some things. Within 10
years the number of different families became almost un-countable. I think these
guys spent a *lot* of time coming up with weird reasons to add a new line of logic
to their portfolio.

The good news is that faster is better in silicon CMOS (except in weird cases like above). 
About all you need to check is:

1) Is it CMOS or TTL levels? (AC vs ACT , HC vs HCT, etc) get the right one.
2) Is it as fast as the stuff I’m replacing ?(check toggle rates or delay) simple answer
is almost always yes if HC and AC are the “comparison standard”.
3) Will it handle my supply? Some of the newer stuff is 3.3V only. 

There are some odd cases like buffer gates. If you are crossing one of those, just be sure
you cross it to a buffer and not to a simple inverter. Drive levels can matter. 

====

Simple answer - sure they are better / lower noise floor / better ADEV / faster / cheaper 
/ easier to layout than the old stuff. They probably are lower power as well. 

Bob

> On May 31, 2015, at 2:06 PM, Dan Watson <watsondaniel3 at gmail.com> wrote:
> 
> Hi,
> 
> Has anyone used or experimented with the 74LVC series of ICs? I have found
> them quite useful in projects. Supply voltage of 2-5V, and two inverters or
> a single gate or flip flip in a SOT package. They make for much cleaner
> layouts than large DIPs.
> 
> I'm wondering if they are acceptable replacements for 74HC, AC, etc in
> timing circuits.
> 
> A couple examples of the series I'm referring to:
> 
> http://www.ti.com/lit/ds/symlink/sn74lvc2g14.pdf
> http://www.ti.com/lit/ds/symlink/sn74lvc1g175.pdf
> 
> 
> Thanks,
> 
> Dan
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



More information about the time-nuts mailing list