I have to design an unusual device, with a small AVR (not yet selected) at its heart, that runs off 3 D or C cells. When running the device will draw maybe 200 mA, but it only runs for an hour or so once a week, or as little as once a month. It has to be battery powered, no chance of being powered off the AC line. Further, this device needs to be turned on and off with a passing magnet (so, magnetic reed switch). That means it will be in a sleep mode for most of its life, and I just want to be sure I'm not missing anything obvious.
First a simple calculation. If I budget for a 10% energy loss in sleep mode vs the run energy, that's 20 mAH over 1 month, or 27 uA allowed in sleep mode. That looks to be one or two orders of magnitude over the chip current in Power down mode. I know I have to factor in any other currents as well.
I'm guessing I can use the reed switch to wake up the device via an INT pin, and of course shutting it down via the same pin shouldn't be a problem.
So, what if anything am I missing at this initial stage? Thanks.