CMOS MAX Vss?

[Magnus Danielson]

>>>>> "c" == cyborg0  <cyborg0 at GlobalEyes.net> writes:

 c> Me and some of my workmates have a problem right now.. 
 c> We are trying to find out the max Vss of MOST cmos gate chips.
 c> I have heard 5V, 15V, 18V, and I have read somewhere that it was only
 c> capable of 5V, but, with so many dissenting views it made me wonder,
 c> since I, too, have heard that CMOS is capable of a higher Vss from
 c> various other sources...
 c> anyone with answers, let me know..

There are several families and they have diffrent speed and Vss.

Everyone should remember that there are pin-compatibles that does not
survive 12V and 15V. The 74HC and 74HCT are 5V.

Not only upper but also lower limits may vary widely between the
families and you better check the datasheets properly, for some may
timings also be critical, so don't forget that (fast enougth isn't
allways the trick, slow enougth migth occur!)

Some examples from my Toshiba databook:

		74HC04	74HCT04	74HCU04
Rec. Vcc min	2 V	4.5 V	2 V
Rec. Vcc max	6 V	5.5 V	6 V
Abs. Vcc max	7 V	7 V	7 V
tTLH typ @4.5V	8 ns	8 ns	8 ns
tPLH typ @4.5V	10 ns	13 ns	8 ns
cin typ		5 pF	5 pF	9 pF

So there are a number of parameters that may change depending on
family. I would strongly recommend a thorough check on critical
parameters on each component and consider things like availablility as
well. There is NO overall generic Vcc maximum for CMOS components.
Also, recall that things like timing may change with supply voltage.

If you pick a family then you will mostly share the same Vcc
max. Outside the family you can assume close to nothing.

An 4046 and 74HC4046 isn't exactly the same thing, and you need to
check the design to see if they may be exchanges for each other.
There are designs where they do exchange for each other, so it is not
impossible but it is not universally true.

Assume nothing - ensure that you know!

The web is a great place to find out about these things, most serious
manufactors have full datasheets for these components.

Cheers,
Magnus