picoPower™ Technology: Hammering Down Power Consumption — Maintaining Performance

The Ultimate Low Power Solution
Embedded applications normally spend their time either in active or in sleep mode – some periods the CPU is running code and processing something while the rest of the time the microcontroller is waiting or idling and should stay in a low power mode. With more and more portable and hand-held applications, wireless networks and sensors, and battery operated appliances, sleep modes have become important. Nevertheless it is equally important that the MCU is able to deliver performance without ruining the power budget while the CPU is active. Atmel's picoPower™ technology saves energy while maintaining MCU performance. picoPower enabled microcontrollers incorporate a number of techniques for reducing the power consumption in both active and sleep modes and still react quickly from any sleep mode.

With AVR MCU's embedded designer have the tools to easily tune an application's power behavior throughout the product lifetime.

Sleep Modes
AVR microcontrollers have different modes of operation, including active-, idle-, and different sleep modes. Once in a sleep modes an external interrupt on I/O-pins will still wake the AVR device up to active mode in only 6 clock cycles!

True Low Voltage Operation
Lowering the operating voltage is the most efficient way to reduce the power consumption in active mode. If the MCU is able to deliver high throughput running off a ultra low supply voltage, the time spent for calculations and program execution can be kept short. New AVR MCU families use a single-cycle CPU and are fully operative with a power supply of only 1.6 volts including all analog modules and program/data memory. However, not all microcontroller brands are able to deliver when the available power source is limited. With a higher minimum VCC or a MCU where all functions doesn’t work below 2 Volts, the increased energy consumption reach close to 35% instantly! With picoPower devices your product will maintain its agility and accuracy well within a strict power budget, and still have working ADC, Flash, EEPROM, and operative internal oscillators. For battery operated products this is of the highest priority, and allows for deeper battery discharge or safe operation directly from a 1.8V +/-10% power supply. The following figure shows how the systems average power consumption is kept at a minimum with a low power supply and maintained high throughput during active periods.

Minimized Leakage Current
For applications spending most of their time in sleep mode, a microcontrollers leakage current is essential since this current cannot be removed or turned off. The lower these leakage numbers are the better it is for your design. AVR MCUs include Atmel's picoPower technology that reduces the leakage current to only 100 nA while maintaining full RAM and register retention.

Dynamic Clock Gating
The AVR peripherals can be disabled so the power consumption is reduced to zero for an unused peripheral. From software the clock to each peripheral can be dynamically turned on and off during program execution. For AVR XMEGA devices dynamic clock scaling and dynamic clock switching are very efficient ways to save energy without reducing performance or functionality.

Sleeping BOD
AVR picoPower devices have an accurate Brown-Out Detector(BOD) that can be automatically turned off in sleep modes when the CPU is halted and the BOD is not needed. AVR XMEGA comes with a BOD that also can work in sampled mode. With 1 ms reaction time this consumes a mere 1 µA while accuracy is remained, and is perfect for applications or periods with stable operating voltage.

Flash Sampling
Since reading the Flash is CPU speed independent, the integrated Flash memory will be idle most of the time due to the fast instruction fetch with operating frequencies below a few MHz. As an embedded designers the AVR microcontroller's Flash sampling automatically disables the Flash when it is not read and the power consumption is reduced significantly without software or program intervention.

Ultra Low Power 32 kHz Crystal Oscillator
AVR MCU's Real Time Counter keeps running while the rest of the device is in sleep mode. Using an external 32.768 kHz Crystal Oscillator the RTC operation only consumes 650 nA. Wake up is still only 6 cycles and can be from either reset or interrupt. For AVR XMEGA devices security functions like Sampled BOD combined with Watchdog can be enabled and will only add 1 µA. This allows for asynchronous time keeping an wake-up with minimum battery drain.