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line driver am26ls31

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Full Member level 6
Nov 29, 2010
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i am using dspic33ep512mu810 micro controller it operates at 3.3v vcc
i am interfacing this microcontroller with am26ls31 line driver ic that operates in 5v vcc

the input to the line driver is 3.3v microcontroller the output of am26ls31 is 5v
in the datasheet of am26ls31 says that it accepts
VIH High-level input voltage = 2v
Low-level input voltage=0.8v
my doubt is that whether it will work good.


next time please post a link to the datasheets. Directly to the manaufacturer site.

I didn´t read the datasheet.
* you say VIL = 0.8V (indeed: <= 0.8V) ... and I guess that the VOL of the DSPIC is less than this, I see no problem.
* you say VIH = 2.0V (indeed: >= 2.0V) ... and I guess that the VOH of the DSPIC is higher than this, I see no problem.

What exactly is your concern?

Are you worried about "good"? There is no good/bad/mediocre in datasheets. Keep on the specifications and it will work reliably.


The LSTTL version will be fine as long as you're OK
with about 400uA IIL.

CMOS versions will see elevated Idd / Icc with weakly
driven inputs, a 26CT31 would be better than a 26C31
due to input buffer design but still may end up with
higher Idd at Vin=3.3 (or 3.16 or 3.0) than the TTL if
the '31 front end is held there.

You may find (though fewer) CMOS 3.3V RS-422 drivers.
They have a hard time with loaded output difference at
low temp due to the blocking diode / Darlington emitter
(depending on whether CMOS, or TTL technology) but
that's more of a spec-marginality than a functional impact
kind of problem - a slight miss on noise margin, like 9.5:1
instead of 10:1.

And it's likely that your 26LS31 could run "OK" (less drive
but perhaps adequate) at the same 3.3V rail. You may not
have a spec table for that condition, but might find that
has been characterized at some point.

You have less noise margin, so at minimum make sure your supply rail
is "quiet". Quick way of telling that is put your scope on AC, infinite
persistence setting, say 500 mV / box, and look at pk-pk noise.
Both micro and driver.

You can do the test on DC as well, but at less resolution (vertical V/box).

Keep in mind when using bypass caps not all caps, for same C, are as
effective, choose wisely. A mix of bulk cap and ceramic.


Note OSCON in this chart is polymer tantalum.

Regards, Dana.

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