Low-Power Modes

Typical modes: idle (CPU stopped, peripherals running), standby/stop (most clocks off, RAM retained) and deep sleep/shutdown (only RTC or wake pins powered, µA or less).

Average current:

$I_{avg} = \frac{I_{active} t_{active} + I_{sleep} t_{sleep}}{t_{active} + t_{sleep}}$

A sensor that wakes for 10 ms every minute at 10 mA and sleeps at 5 µA averages about 6.7 µA — over a decade of life on paper, in practice limited by battery self-discharge. Remember LEDs, regulators' quiescent current and pull-up resistors also drain the battery.