Re: CMOS logic level range
- From: John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 11 Mar 2007 09:29:38 -0500
On Sat, 10 Mar 2007 18:06:00 -0600, "Anthony Fremont"
<spam-not@xxxxxxxxxxx> wrote:
John Fields wrote:
---
Yup. I misinterpreted the "typicals". With a 5V supply, if you
drive the input to somewhere between 0V and 1.5V the output is
guaranteed to switch, and if you drive the input to somewhere
between 3.5V and 5V the output is also guaranteed to switch.
I sometimes wonder why they state "typical" specs. I guess it's a bit of a
sanity check and gives one a decent idea about how the part performs in
general, but depending upon them in a design wouldn't seem to be a very good
idea IMO.
---
It's all about what you're willing to trade off. For example, if
your design _must_ work, all the time, you design around worst case
and make sure that the devices driving logic inputs _always_ rise
above 3.5V for a high and fall below 1.5V for a low. The penalty
you pay for the robustness is speed, since it takes longer to get to
guaranteed switching points than it does to get to the typicals.
The penalty you pay for using typicals is that you'll have some
product fallout because the typicals aren't guaranteed.
--
JF
.
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