[time-nuts] CMOS level difference for LTC6957-3 and AD9852

d0ct0r time at patoka.org
Fri Apr 25 17:33:46 UTC 2014

To whom it may concern, here is the note regarding of CMOS level 
difference for two product AD9852 from AD and LT6957 from Linear.

My attempts to feed AD9852 directly from LTC6857-3 has failed. AD9852 
just ignored the REFCLOCK signal coming from LTC6957-3. So, I'll need to 
think about some solution how to match the levels and do not impact the 
source signal too much.

(Received from tech. department of AD):
... the logic levels for the AD9852 and LTC6957
don't line up. From page 5 of the AD9852 datasheet, VIH minimum is
2.3V whereas the LTC6957 says it's VOH could be as low as 2.08V. This
means the LTC6957 could output 2.08V for a logic high, but our part
won't recognize it as it needs at least 2.3V to be a logic high.

It's the same problem for low logic voltages. The AD9852 datasheet
says VIL max is 1V whereas the LTC6957 says it's VOL max is 1.63V or
1.67V depending on the temperature range of your part. So the LTC6957
could output 1.63V for a logic low, but our part won't recognize it as
it needs a voltage below 1V to be a logic low.




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