DS3231 vs MAX31328 RTC

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n2tia
 
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DS3231 vs MAX31328 RTC

Post by n2tia »

tl;dr: Why exactly did Analog Devices come out with the MAX31328, which afaik, seems only to be used in the Adafruit/Macetech Chronodot 3.0?
Was it simply to repackage into the super-tiny LGA 10 package (from the DS3231's SO 16)?
Why did the MAX31328 drop the DS3231SN's +-2.5ppm (0-40C) spec to simply keep +-3.5ppm -40-+85?
(not that the 1ppm (32 secs/yr) difference is really a problem)
I've now used both and cannot find any other differences in the spec sheet?
Will DS3231s soon go EOL?
Does Adafruit plan to update its various RTC breakouts with the MAX31328?
Any insights welcome...

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adafruit_support_mike
 
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Re: DS3231 vs MAX31328 RTC

Post by adafruit_support_mike »

n2tia wrote: Sun Apr 02, 2023 10:13 am Why exactly did Analog Devices come out with the MAX31328
Because they expect to make a profit selling it?

Given the chip shortage and shipping problems of the last couple of years, it may be something they could get fabbed and shipped while DS3231 production was stalled for a couple of years. The chip you can sell today is worth more than the chip you can't build at all.

For the rest of your questions, those are things you'd need to ask Analog rather than us.

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macegr
 
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Re: DS3231 vs MAX31328 RTC

Post by macegr »

Garrett here, from macetech. We switched to the MAX31328 because the DS3231 was unavailable, or like 15 dollars. However, I examined every detail before making the switch: I was looking at other TCXO RTCs, but was extremely reluctant to choose anything that would require different drivers or provide different performance.

The MAX31328 is EXACTLY the same as the DS3231, except in a smaller package. Here's why:
  • Every register is identical in address and function to the DS3231. This was a huge discovery when I was facing the possibility of changing the ChronoDot to be completely incompatible with previous versions.
  • Nearly every electrical specification is the same, timekeeping current is a little lower. Not much, and could be due to process change or a different test setup.
  • The accuracy spec is actually identical. The DS3231 always had a 2ppm spec for the 0C to 40C range, and a 3.5ppm spec for the -40C to 85C range. The MAX31328 just quotes the 3.5ppm spec for the part's entire operation range, same as the DS3231. The stability charts in the datasheet appear to promise even better; in any case, the top-level promise of 2 minutes per year is still on both datasheets. The datasheet at least is way better, with chart scales that make more sense.
The above leads to my suspicion that the silicon is either identical, or the same IP on a die shrink for cost savings. Not sure how they fit the crystal in there actually, might have to open one up.

The chip came along at exactly the right time, and feels like a nice upgrade from the chonky DS3231 packaging.

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