4.4 picoPower/Power Management and Sleep Modes
The essence of an AVR® picoPower device goes beyond merely the various picoPower features included. The design methodology, the process geometry, and even the types of transistors used are all essential power-saving parts of a picoPower device. All picoPower devices are designed from the ground up for low power consumption utilizing AVR’s proprietary low leakage processes and libraries to provide industry leading low power consumption in active and all sleep modes.
The white paper "Innovative Techniques for Extremely Low Power Consumption with 8-bit Microcontrollers" and the application note "AVR4013-picoPower Basics" give a more in-depth look at the picoPower features.
BOD Disable
When the Brown-out Detector (BOD) is enabled by BODLEVEL fuses, the BOD is actively monitoring the power supply voltage during a sleep period. To save power, it is possible to disable the BOD by use of software for some of the sleep modes. The sleep mode power consumption will then be at the same level as when BOD is globally disabled by fuses. If BOD is disabled in software, the BOD function is turned off immediately after entering the sleep mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe operation in case the VCC level has dropped during the sleep period.
When the BOD has been disabled, the wake-up time from sleep mode will be approximately 60 μs to ensure that the BOD is working correctly before the MCU continues executing code.
BOD disable is controlled by the BOD Sleep bit in the MCU Control Register (MCUCR.BODS). Writing this bit to '1' turns off the BOD in relevant sleep modes, while a zero in this bit keeps BOD active. The default setting, BODS=0, keeps BOD active.