ATtiny87-15XZ datasheet(45/282 Pages) ATMEL

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7728D–AVR–07/09

ATtiny87/ATtiny167

5.8

Minimizing Power Consumption

There are several possibilities 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.

5.8.1

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. Refer to Section 17. “ADC – Analog to Digital Con-

verter” on page 191 for details on ADC operation.

5.8.2

Analog Comparator

When entering Idle mode, the Analog Comparator should be disabled if not used. When enter-

ing ADC Noise Reduction mode, the Analog Comparator should be disabled. In 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. Refer to Section 18. “AnaComp - Analog Comparator” on page

211 for details on how to configure the Analog Comparator.

5.8.3

Brown-out Detector

If the Brown-out Detector is not needed by 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. Refer to Section 6.1.5 “Brown-out Detection” on

page 51 for details on how to configure the Brown-out Detector.

5.8.4

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. Refer to Section

6.2 “Internal Voltage Reference” on page 53 for details on the start-up time.

Output the internal voltage reference is not needed in the deeper sleep modes. This module

should be turned off to reduce significantly to the total current consumption. Refer to “AMISCR

– Analog Miscellaneous Control Register” on page 190 for details on how to disable the inter-

nal voltage reference output.

5.8.5

Internal Current Source

The Internal Current Source is not needed in the deeper sleep modes. This module should be

turned off to reduce significantly to the total current consumption. Refer to “AMISCR – Analog

Miscellaneous Control Register” on page 190 for details on how to disable the Internal Current

Source.

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