I would have thought better.

I built a nixie clock from Tubeclocks.com http://tubeclocks.com/.  Granted it is in a pretty constant temperature, but I doubt that clock varies less than 3 seconds per year.  Peter, the designer, sent me some code that takes a 1PPS but I never got it running as I liked the fact that it was undisciplined (like my kids) and still incredibly accurate.  I just checked it as it had been running 4 months since I moved it to my new office and I doubt is off 1/5th a second.

Regards,

Jerry

On Tue, 6 Mar 2018 22:59:34 +0000
Mark Sims holrum@hotmail.com wrote:

Sigh There are a couple of things wrong with that description.

1. The part is from Microcrystal, so you can believe the specs
   they publish with high confidence. This also means this is probably
   the exact same chip you will find in Swiss quartz watches.
   (Microcrystal is part of the Swatch group and the main supplier
   of 32kHz oscillators and electronics for the Swiss watch industry)

2. The 22nA is the typical consumption in auto-cal mode.
   Max (the number you should design with) is 32nA. Keep in
   mind this number is for the chip alone, no external connection.
   It also includes the implicit condition that all input pins are
   at valid voltage levels. If a pull up/down resistor is too weak
   (because you tried to safe a few more nA) it will result in
   pins being driven by leakage currents, possibly reaching invalid
   voltage levels, which in turn will cause shot-through currents
   through the input stages, increasing the power consumption 10 fold
   at least, 1000 fold easily.

3. The current ratings are at 25°C. Going higher means also
   an increase in power consumption. How much, is not specified.

4. The 3minutes per year number comes from the +/-3ppm first year
   aging. This is, as usual, at 25°C and is on top of the typ. +/2ppm
   time accuracy. So, the real accuracy is more like 5min after the first
   year... when running from Xtal all the time!
   Which has a typ. 60nA/max 80nA current spec!
   Taking temperature into consideration, assuming something in the order
   of 10 minutes per year is probably more realistic... if you stay
   close to 25°C. The quadratic nature of the temperature dependence
   for tuning fork X-cut crystals causes high deviations pretty quickly
   (In one of the devices I designed, the 10ppm spec of the crystal
   suddenly became 300ppm when taking the whole temperature range at
   which it had to operate into consideration)

5. The precision of the auto-cal mode is not specified. It can be
   litterally anything. Especially considering that the datasheet
   talks about using it "several hours at Backup Supply Voltage,"
   i.e. as an emergency measure when the normal power supply is lost.

    	Attila Kinali
   

--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

Hi

Assuming you are going to run it off a battery. What’s the self discharge
rate on a reasonable battery?

Bob

On Tue, 6 Mar 2018 21:57:32 -0500
Bob kb8tq kb8tq@n1k.org wrote:

With supply currents below 100nA you can assume that you are likely
to be limited by the self-discharge using coin sized LiMnO2 cells
(e.g. a CR2032 is specced in the order of 100-300nA self-discharge).
For the smaller cells, you have to check which one is larger, but
they are of the same order of magnitude.

			Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

This is interesting. When you talk of self discharge, is there any way of harnessing that. Is that what the chip manufactures are doing?

"The power of accurate observation is commonly called cynicism by those who have not got it. »
George Bernard Shaw

On Thu, 8 Mar 2018 00:33:58 +0100
Mike Cook michael.cook@sfr.fr wrote:

No. It's a chemical reaction inside the cell. The energy is turned
into heat directly and never leaves the cell in a usable form.

		Attila Kinali

--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

Hi

Self discharge = current flowing through the internal elements of the cell (plus
other long term degradation effects).

Bob