[sdiy] 74HCxxx or CD40xxBE for long term reliability ?

Michael E Caloroso mec.forumreader at gmail.com
Sun Sep 27 16:53:26 CEST 2020


I'd use TTL.  Besides being more reliable, you can use neat tricks
like tying OC outputs into wired-OR which isn't possible with CMOS.

1970s ARPs used the A series CMOS.  Their OEM was RCA and their fab
process yielded CMOS that did not have a long life.  RCA never put
input overvoltage protection in their A series either.  Motorola CMOS
from the same era didn't seem to suffer the life shortage.  Modern
CMOS is more rugged although ESD precautions are still the rule.

CMOS have the edge on supply current though.  Current draw is
primarily during switching states, steady state they draw a trickle of
current.  Just make sure your PSU regulates really well with changes
in current demand.

MC

On 9/27/20, Roman Sowa <modular at go2.pl> wrote:
> if supply current would not matter, for the sake of long term
> reliability I would try to avoid CMOS chips as they are much easier to
> damage by ESD than bipolar ones.
>
> Now if HC is more long term reliable than CD or vice versa, I'd like to
> hear about that too from a professional working on chips reliability (is
> anyone working on that at all?), as there may be more reliability
> dependendce on manufacturer's fab choice than the logic family. In order
> to work at higher voltage, the CD chips use bigger gate silicon process
> so in theory they may be more difficult to destroy. But all today's
> chips have some input protection anyway.
>
> I choose CD4000 over other logic families only when I want slower edges
> of my signals, or higher than 6V supply voltage. There's no other
> advantages IMHO.
>
> Roman
>
>
> W dniu 2020-09-26 o 21:12, Jean-Pierre Desrochers pisze:
>> On a 5volt based supply project,
>> If you had to use logic IC's on a new design
>> And the supply current would not matter
>> Would you use 74HCxxx or CD40xxBE for long term reliability ?
>> I know ARP used mostly CD40xxBE family in their 70's synths
>> when logic was needed.
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
>




More information about the Synth-diy mailing list