[time-nuts] Ultra low power RTC

Bob kb8tq kb8tq at n1k.org
Wed Mar 7 11:33:15 EST 2018


Hi

I’ve designed watch guts (long ago). It was at a time that you used 
an analog (motor) movement if you wanted really low power. The CMOS
/ LCD’s of that era were power hogs by comparison. 

What you can put in a small / thin  watch isn’t what you would use on a 
RTC board. My suspicion is that the leakage from a number of sources will 
indeed dominate the actual power consumption in a random build
sort of application. (At least compared to 10’s of nano amps of power
into the chip). 

Bob

> On Mar 7, 2018, at 11:03 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Wed, 7 Mar 2018 08:27:00 -0500
> Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Since we don’t often *need* the smallest cell made *and* we’re probably 
>> talking lifetime of the cell….. does 22 na vs 33 na matter?
> 
> Not really. It starts to matter when you are space limited and don't
> have space for a CR2032.
> 
> At this level, though, every tiny bit of leakage matters. Finger prints,
> dust, humidity, FR4... Going below 1µA in current consumption is like
> going below 10^-12 in frequency stability, suddenly 1M is a low resistance.
> 
>> Based on the previous data on the chip, I think I would just run the crystal
>> all the time. 
> 
> The the watches (quartz with analog dials) I have run >5 years
> on their batteries, an I am pretty sure they don't have a CR2032.
> And at least one of them must have a TCXO.
> 
> 
> 			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
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