Re: [CAD_CAM_EDM_DRO] CMOS supply rails

Bill Vance wrote:

>
> Howdy;
>
> I'm starting to get some parts and pieces together for some experimental DRO
> circuits, but I've got a question I haven't been able to find an answer to.
>
> The original A and B series CMOS chips, as well as the C series, (74CXX) have a
> plus Volts rating of +15 to +18 Volts. The HC series, (74HCXX), seems to be
> much easier to find than the C series, but the only data I've been able to find
> on them shows a +5 or +6 Volt supply rail. Does the HC series have the same
> rating as the others, but use the +5 or +6 Volt numbers to show compatability
> with TTL, or what?
>
> Thanks in advane.
>
> Bill

Hello Bill,

I have summarized some of the charaterisitics below. I rounded off a few
values so might disagree slightly with data books.

I cannot find my data books for 4000A or 74C at the moment. As I recall,
74C was about the same as 4000B electrically but had pinouts that
matched the 74 series TTL logic.

One of the things I learned the hard way is that CMOS inputs should
NEVER be live when the chip is unpowered. That means that you should not
use a CMOS device as the input to a board or equipment unless you can
guarantee that the signals feeding it will be powered down before the
CMOS device is powered down. CMOS input voltage must always be within
the power supply voltages applied to the CMOS device.

Use TTL devices for inputs to boards and equipment. That way the power
down sequence does not matter.

4000B
Power supply voltage 3 volts to 18 volts.
Input is low if less than 30% of supply voltage.
Input is high if greater than 70% of supply voltage.
Output low is at or near 0 volts.
Output high is at or near supply voltage.
Input must be between zero volts and supply voltage to not damage.

74LS
Power supply voltage 4.75 volts to 5.25 volts
Input is low if less than 0.8 volts.
Input is high if greater than 2.0 volts.
Output low is less than 0.4 volts.
Output high is greater than 2.4 volts.
Input must be between -0.5 volts and +15 volts to not damage.

74HC
Power supply voltage 2 volts to 6 volts.
Input is low if less than 25% of supply voltage.
Input is high if greater than 70% of supply voltage.
Output low is less than 0.1 volts.
Output high is greater than 88% of supply voltage.
Input must be between zero volts and supply voltage to not damage.

74HCT
Power supply voltage 4.5 volts to 5.5 volts.
Input is low if less than 0.8 volts.
input is high if greater than 2.0 volts.
Output low is less than 0.26 volts.
Output high is greater than 3.7 volts.
Input must be between zero volts and supply voltage to not damage.