5 Nov
2011
5 Nov
'11
10 p.m.
On Nov 5, 2011, at 11:12 PM, Chuck Guzis wrote:
On 5 Nov 2011 at 19:24, Eric Smith wrote:
Yeah, a 3.3v CMOS output will still be putting out higher than many 5v TTL chips output. A
surprising number of modern low-voltage micros still have 5v-compatible inputs. I worked
with a seriously irritating TI DSP that, among other insults, only took 1.8v inputs (no
higher, no lower). We had 12 voltage rails on that one AMC card (about 2"x5",
highly integrated).
We did, however, like the 74AVC4T245 for voltage translation. That almost fits your
dual-supply bill, only the AVC parts don't go up to the full 5v. For that, your best
bet would be in the LVC family; they have some dual-rail '245 and similar equivalents
(e.g. the SN74LVC8T245). Nothing in DIP, though, so if you really wanted that you'd
have to mount them to surfboards (I really like the ones by Bellin at
http://www.beldynsys.com/; not cheap, but pretty nice protoboards the do mount up
nicely).
- Dave
Chuck Guzis wrote:
If it's a 3.3v microcontroller on the other side, it's a good reason
for selecting one with 5V tolerant inputs, I guess. At least you can
use plain old HCT in both directions. Do there exist any split supply (3.3V/5V) level
converter chips in
DIP?
I don't think so. That's why I use 74LVC parts for the 5V to 3.3V
direction, and 74HCT for the 3.3V to 5V direction, if 5V CMOS levels
are actually needed. Usually they aren't.