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DS3231M - Improve accuracy with Aging register?

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PCB.Wiz:

--- Quote from: Peabody on May 04, 2023, 02:47:54 pm ---  But the two M parts - one possibly genuine and one definitely fake - ended up with optimum settings of -44 and -19.  They come from the factory with Aging set to zero.  So they are off a good bit.

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They may adjust these offset to allow for some aging, and sometimes the limits on the specs, mean room temperature is off by a bit in order to fit the curves.


--- Quote from: Peabody on June 28, 2023, 04:37:40 pm ---
I found that the optimum setting changes over time as the RTC, uh, ages.  And in all cases aging makes it run slower.  My only genuine DS3231SN started out optimizing at an aging register setting of +1, but after a couple months it now optimizes at -5.

My several-years-old part marked DS3231SN, but which behaves like a DS3231M, started at -44, and is now at -46.  So it was already old when I started these tests.  I think the changes diminish as the parts get older, but I don't think they ever stop.

And my new official DS3231M part started off at -19, but is now at -24.  In all cases the RTCs have been kept running.  I don't know if aging slows down if they are powered down most of the time.

One complicating factor is temperature.  All of the tests were done at room temperature, but that has changed about 7 degrees F as we've moved into summer.  Both SN and M parts have built-in temperature adjustments, but I don't know how well they work, or if there's any difference in how well they work.

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You can expect to be moving along a temperature curve here, and they do not show how the trim steps work - on parts that do show that, it's an expected noise of the LSB trim size,as they walk along a table.
Crystals often have a hysteresis effect where the temperature they were in the past, influences the frequency now, a little.

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