Rainbow Electronics ATtiny43U - Manual (Page 33)

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8048B–AVR–03/09
peripheral should in most cases be disabled before stopping the clock. Waking up a module,
which is done by clearing the bit in PRR, puts the module in the same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped
7.4 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.
7.4.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. See
“Analog to Digital Converter” on page 115 for
details on ADC operation.
7.4.2 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 dis-
abled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
independent of sleep mode. See
“Analog Comparator” on page 112 for details on how to config-
ure the Analog Comparator.
7.4.3 Brown-out Detector
If the Brown-out Detector is not needed in the application, this module should be turned off. If the
Brown-out Detector is enabled it will be active in all sleep modes and, hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. See
“Brown-out Detection” on page 50 and “Software BOD Disable” on page 32 for details
on how to configure the Brown-out Detector.
7.4.4 Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, 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. See
“Internal Voltage
Reference” on page 51 for details on the start-up time.
7.4.5 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 consump-
tion. See
“Watchdog Timer” on page 51 for details on how to configure the Watchdog Timer.