ATMEGA162 datasheet(46/325 Pages) ATMEL

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ATmega162/V

2513I–AVR–02/07

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 possi-

ble, 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.

Analog Comparator

When entering Idle mode, the Analog Comparator should be disabled if not needed. 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 Volt-

age Reference will be enabled, independent of sleep mode. Refer to “Analog

Comparator” on page 197 for details on how to configure the Analog Comparator.

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. Refer to “Brown-out Detec-

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

Internal Voltage Reference

The Internal Voltage Reference will be enabled when needed by the Brown-out Detector

or the Analog Comparator. 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 imme-

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

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 53 for details on how

to configure the Watchdog Timer.

Port Pins

When entering a sleep mode, all port pins should be configured to use minimum power.

The most important thing is to ensure that no pins drive resistive loads. In sleep modes

where the I/O clock (clk

I/O) is 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 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 68 for

details on which pins are enabled. If the input buffer is enabled and the input signal is

left floating or have an analog signal level close to V

CC/2, the input buffer will use exces-

sive power.

JTAG Interface and

On-chip Debug System

If the On-chip debug system is enabled by the OCDEN Fuse and the chip enter Power

down or Power save sleep mode, the main clock source remains enabled. In these

sleep modes, this will contribute significantly to the total current consumption. There are

three alternative ways to avoid this:

•

Disable OCDEN Fuse.

•

Disable JTAGEN Fuse.

•

Write one to the JTD bit in MCUCSR.

The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP

controller is not shifting data. If the hardware connected to the TDO pin does not pull up

ATMEGA162 Datasheet(PDF) 46 Page - ATMEL Corporation

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