ATA8742-PXQW【PDF 52/238 页】MCU W/TRANSMITTER ASK/FSK 24QFN

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9151AINDCO07/09

ATA8742

15.7 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 devices 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.

15.7.1

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 154 for

details on ADC operation.

15.7.2

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 150 for details on how to config-

ure the Analog Comparator.

15.7.3

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 by the BODLEVEL Fuses, 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. See Brown-out Detection on page 59 for details on how to

configure the Brown-out Detector.

15.7.4

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 60 for details on the start-up time.

15.7.5

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 60 for details on how to configure the Watchdog Timer.

15.7.6

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

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 consumed by the input logic when not needed. In

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