ATmega162V-8AI datasheet(46/324 Pages) ATMEL

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2513K–AVR–07/09

ATmega162/V

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.

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 Compar-

ator 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, indepen-

dent of sleep mode. Refer to “Analog Comparator” on page 195 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 Detection” on page 50 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 inter-

nal 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 52 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 consump-

tion. Refer to “Watchdog Timer” on page 52 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 67 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 excessive 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 the logic level,

power consumption will increase. Note that the TDI pin for the next device in the scan chain con-

tains a pull-up that avoids this problem. Writing the JTD bit in the MCUCSR register to one or

leaving the JTAG fuse unprogrammed disables the JTAG interface.

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