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[on:]

I reckon this question falls under 'power'

According to the data sheet, the active current is 700uA, & the standby current is 160uA.  But on page 3 is says the time keeping battery current is only 1.5 uA. 

So, it seems that if I keep the chip's Vcc off, it'll run on battery power quite quiescently!
17 years on a 225mAh CR2032, if I calculated correctly.

If I'm running a 5 volt system, could my Atmega328P supply the power to this directly from an I/O pin?  (DS3234 is 2.0-5.5 volt).

So then my atmega328 will be the only thing running all day, and it seems that'll be less than a microamp when asleep.  This is all sounding hopeful!

[Reply #1 on:]

To highlight my question then, can I power the DS3234 RTC in the same way as this DS1307?
http://www.gammon.com.au/forum/?id=11497&reply=3#reply3

[Reply #2 on:]

It says in the write up, "The RTC chip is actually "alive" all the time from its battery backup, it just is not allowed to use I2C without external power. So we don't have to wait long before we use it."
Is your DS3234 a chip by itself or is it on a PCB with a battery?

[Reply #3 on:]

Sorry, I meant to post the data sheet.
http://www.sparkfun.com/datasheets/BreakoutBoards/DS3234.pdf

The DS3234 is SPI, not I2C, like the DS3232.
The SPI doesn't operate when Vcc is lower than Vbat. But I'm still not sure if the alarms function on Vbatt. I've written Dallas to find out.
My chip will be installed on a custom board.

[Reply #4 on:]

The time keeping current on those things can be less than 1ua (typically around 500na, and one of a simpler one, ds1302/ds1307 can be around 100na), if you turn off all communications and output.

If you are really after power consumption, look for the version with silicon oscillators.