Re: [CAD_CAM_EDM_DRO] CMOS supply rails

Thanks again, gang. As usual, its been an education.

Bill

On Thu Nov 4 17:09:29 2004 Tom Hubin wrote:

>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.


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