5.1.3 Clock Source Selection

For optimal power consumption, selecting appropriate system clock for MCUs is very much essential. Instead of using higher system clock and prescaling, switch to a different and slower clock source.

For example, to generate a 16 MHz system clock, using PLL and the 2 MHz RC oscillator as a reference is preferable over the 32 MHz RC oscillator with prescaling to 16 MHz. Usage of external clock sources may also be a good choice, especially if they are already available in the system.

The wake-up delay for the MCU depends on which clock source is used for the system clock. One way to reduce this delay is to switch between clock sources so that the MCU goes to sleep and wakes up with a fast responding clock source.

Minimize power consumption by switching clock sources rather than relying on prescaling
          alone for reducing clock rates.