Power saving mode Microcontrollers
- Why is reducing power consumption is important?
- Hardware vs. Software methods
- The need to balance power
- consumption with performance needs
- !Examples
How to Save Power
- !Power Down Modes
- !Clocking Systems
- !Interrupts
- !Peripherals
POWER-DOWN MODES
Control clock frequency POWER-DOWN MODES
Control CPU power
CLOCKING SYSTEMS
Current is wasted while CPU waits for stable clock
Most low-power MCUs have “instant on clocks”
INSTANT-ON CLOCKS
Some have two-stage clock wake up
Provides a low freq. clock while high freq. clock stabilizes
Can take 1ms longer
On these devices, CPU may be operational in 15us
But runs on an incorrect frequency
CPU consumes less current at low frequencies
Inaccurate frequency can relate to inaccurate timing
If accurate timing is necessary, the CPU must wait for the clock to stabilize.
INTERRUPTS
Goes hand in hand with system clock flexibility
Bring MCU out of low-power mode
More interrupts, more currentsaving flexibility
Without interrupt capability, MCU must poll the keypad or buttons often
Controlling polling requires a timer
Additional current INTERRUPTS
With interrupts, CPU can sleep until a button is pushed
WHAT ARE MCU PERIPHERALS?
Peripherals are components on a chip which have programmable input/ output capability
Examples:
Timers
Event Counters
PWM generators
ADC/DAC
LOW POWER PERIPHERALS
Some MCUs don’t have low power peripherals
Two types of low power peripheral ability
Individual enable/disable
Automatic enable/disable
A true low-power peripheral is one that consumes no current when not in use
SPECIAL DETAILS OF POWER SAVING ON MCUS
In today’s battery-driven world, power saving is a must for many consumer-based applications
Most modern-day microprocessors/controllers have a variety of onboard power-saving features
Compare TI vs. Microchip
TI
MSP430 Line of “Ultra Low Power MCU’s”
Microchip
PIC nanoWatt eXtreme Low Power MCU’s
Refer to Microchip website for more information about different MCU’s
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