Datasheet

33
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
10.7 Extended Standby Mode
When the SM2:0 bits are 111 and an external crystal/resonator clock option is selected, the SLEEP instruction
makes the MCU enter Extended Standby mode. This mode is identical to Power-save mode with the exception that
the Oscillator is kept running. From Extended Standby mode, the device wakes up in six clock cycles.
10.8 Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR controlled system.
In general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as
few as possible of the device’s functions are operating. All functions not needed should be disabled. In particular,
the following modules may need special consideration when trying to achieve the lowest possible power
consumption.
10.8.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering
any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion.
Refer to “Analog to Digital Converter” on page 193 for details on ADC operation.
10.8.2 Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC Noise
Reduction mode, the Analog Comparator should be disabled. In the other sleep modes, the Analog Comparator is
automatically disabled. However, if the Analog Comparator is set up to use the Internal Voltage Reference as
input, the Analog Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will
be enabled, independent of sleep mode. Refer to “Analog Comparator” on page 190 for details on how to configure
the Analog Comparator.
10.8.3 Brown-out Detector
If the Brown-out Detector is not needed in the application, this module should be turned off. If the Brown-out Detec-
tor is enabled by the BODEN Fuse, it will be enabled in all sleep modes, and hence, always consume power. In the
deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Brown-out Detec-
tor” on page 33 for details on how to configure the Brown-out Detector.
10.8.4 Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detector, the Analog Comparator
or the ADC. If these modules are disabled as described in the sections above, the internal voltage reference will be
disabled and it will not be consuming power. When turned on again, the user must allow the reference to start up
before the output is used. If the reference is kept on in sleep mode, the output can be used immediately. Refer to
“Internal Voltage Reference” on page 33 for details on the start-up time.
10.8.5 Watchdog Timer
If the Watchdog Timer is not needed in the application, this module should be turned off. If the Watchdog Timer is
enabled, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this
will contribute significantly to the total current consumption. Refer to “Watchdog Timer” on page 33 for details on
how to configure the Watchdog Timer.
10.8.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The most important thing
is then to ensure that no pins drive resistive loads. In sleep modes where the both the I/O clock (clk
I/O
) and the
ADC clock (clk
ADC
) are stopped, the input buffers of the device will be disabled. This ensures that no power is con-
sumed by the input logic when not needed. In some cases, the input logic is needed for detecting wake-up
conditions, and it will then be enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 52 for