[time-nuts] A look inside the DS3231

Tim Shoppa tshoppa at gmail.com
Sun Jul 30 08:15:57 EDT 2017

On the subject of low-current 32kHz oscillators:

DS3231 spec says typical 1uA for timekeeping and circa 600uA for
temperature conversion. I understand they periodicailly kick the
temperature conversion on but only for extremely short duty cycles and this
is included in the 1uA.

Standard DS12887 spec was 500nA with the oscillator and counter logic
running. This did not have any temperature conversion/compensation.

RCA published a 4007-based 32kHz oscillator that was circa 1uA but I think
that spec was at 1.5V. RCA got a patent on putting a resistor in the drain
of the first stage to slow it down and reduce power consumption to get down
to 1uA. So in the DS12887, Dallas figured out how to go at least a factor
of two lower in power. I would imagine there's a series of patents by watch
companies on this subject as well probably all back in the 1970's and

Tim N3QE

On Sat, Jul 29, 2017 at 2:32 PM, Pete Stephenson <pete at heypete.com> wrote:

> On Thu, Jul 27, 2017, at 09:46 PM, Trent Piepho wrote:
> > Looks like it still says "DALLAS SEMICONDUCTOR" to the left of Maxim.
> > Maybe Maxim only wanted to change the mask enough to find some empty
> > space to sign it?
> It does indeed say "DALLAS SEMICONDUCTOR".
> I managed to get some high-quality photos using the microscope's
> on-board camera and have updated the photo album at
> https://imgur.com/a/0zudj with the newest ones (they're the
> all-rectangular photos below the two circular photos). There's some
> high-resolution composite images.
> Some things I found interesting:
> - There's a section just above the "Maxim" part that has several
> snippets of text ("17A3", "16A3", etc.). In normal light, each of these
> bits of text is a different color, where the colors correspond to
> different layers of the chip. Each bit of text has a different depth of
> focus, indicating they're physically closer or further from the lens.
> Does anyone know what material the colors might correspond to?
> - There's several square grids of circles-in-squares circuit elements. I
> have no idea what these are.
> - I find it remarkable that this circuit can operate on less than a
> microamp during normal usage, including temperature conversion.
> The DS3231 has on-board temperature monitoring to correct the crystal
> frequency: is this something where they would have bothered putting a
> separate sensor next to the crystal itself, or are the die and the
> crystal are close enough and in the same package that they could use an
> on-die sensor like a diode and call that "good enough"?
> Cheers!
> -Pete
> --
> Pete Stephenson
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