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7903A – AVR – 2006/02

time. Idle mode is a shallow sleep mode where only parts of the device are shut down but

the main parts of the microcontroller are running.

The advantage of having multiple sleep modes is the flexibility it provides to shut down any

part of the microcontroller that is not absolutely necessary to the function at hand. The

amount of power that can be saved depends on the mode being using. For example with a

1.8V supply voltage operating at 1 MHz and 25ºC, Atmel’s ATmega165P AVR controller

consumes 340 uA in Active mode, 150 uA in Idle mode, 0.65 uA in Power Save mode and

a scant 0.1 uA in Power Down mode.

Figure 1: Power budget

Since a microcontroller can spend substantial amounts of time inactive, it is important to

consider power consumption in sleep modes as well as active power consumption. Many

designers use a power budget to determine the average power consumption and to

calculate the battery requirements.

Although a great deal of attention is paid to active power consumption, the most important

mode to consider really depends on the duty cycle between the various sleep and active

modes. In applications such as thermostats, keyless entry, or security systems the

processor spends most of its time idle. For these applications, sleep mode may represent

the lion’s share of power consumption and will be the most important parameter to

consider.