picoPower® Technology
Reducing Power Consumption — Maintaining Performance
To meet the tough requirements for portable and battery-operated applications, Atmel has focused on low power consumption for more than ten years. The result is our outstanding picoPower® technology for tinyAVR®, megaAVR®, AVR® XMEGA™ and AVR UC3 microcontrollers.
picoPower technology enables AVR microcontrollers to operate at the industry's lowest power consumption with 650 nA with a RTC running and 100 nA in Power Down sleep. Through a range of innovative techniques, Atmel has reduced power consumption in active and all sleep modes. With picoPower technology the embedded designer can easily reduce the application’s power consumption while maintaining performance.
True 1.6-Volt Operation
With true 1.6-Volt operation, all functions — including ADC, DAC, Flash- and EEPROM memories — operate as normal down to 1.6V. This allows safe operation directly from a 1.8V ±10% power supply. It also enables deeper battery discharge to increase battery life.
Minimized Leakage Current
AVR leakage current is only 100 nA while still maintaining full RAM and register retention. This reduces power consumption for applications spending most time in sleep mode.
To eliminate the leakage current traditionally associated with mixed analog and digital I/O pins, AVR microcontrollers feature a Digital Input Disable Register, which can be used to disable the digital input stage when a pin is connected to an analog source.
A digital input is basically built by a pair of cascaded PNP and NPN transistors. As long as a valid high or low voltage level is applied to the buffer, power consumption is negligible. However, applying voltages in the area of VCC/2 will partially activate both transistors, generating a significant leakage current through the digital input stage as both transistors will open slightly. The Digital Input Disable Register can be used to eliminate this leakage current. In addition, all digital input buffers are even automatically disabled when sleep mode is entered except for those pins used by the input signal to wake the MCU from a sleep mode.
Ultra Low Power 32 kHz Crystal Oscillator
A very low power 32-kHz Crystal Oscillator keeps a real-time counter (RTC) up to date. The AVR XMEGA’s RTC consumes only 650 nA, and the AVR UC3 RTC consumes down to 1.5 uA.
Sleep Modes
The AVR’s many sleep modes allows software to turn off unused modules and clocks to reduce power consumption. Many sleep modes make it is easy to find the perfect fit and fine-tune the setup for any application. The granularity is further enhanced by the innovative Power Reduction Register technology.
When waking up from sleep, the AVR CPU must wait for the selected clock source to start up. This delay can be eliminated by selecting a sleep mode where the relevant oscillator is kept running while the CPU and peripherals shuts down.
Furthermore, intelligent peripherals and proper use of the DMA controller, Peripheral Event System, and SleepWalking feature allow the device to operate for extended periods without waking up the CPU.
Sleeping BOD
Although zero-power Brown-Out Detectors (BOD) can save a lot of power, they are notoriously slow, provide odd detection levels and can require a millisecond to detect a below-threshold voltage. The slow response time could put the controller at risk. Atmel's AVR BOD detects brown-out conditions in 2 microseconds but draws about 20 uA, adding substantially to the Power Down sleep current of 100 nA.
With picoPower technology, Atmel has maintained the high performance and relatively high current of the BOD and saved power by disabling the BOD when it is not needed. This approach results in the lowest overall power consumption and the highest possible performance with accurate detection at 1.8V, 2.7V and 4.5V.
Response time versus Detection Level AVR Brown-Out Detector
Since there is no need for the BOD while the MCU is in the deep sleep mode, the picoPower BOD can be safely turned off in Extended Standby, Standby, Power Save and Power Down modes. The picoPower BOD-disable feature is enabled by the application using a two-step secure operation and is fully automatic. When entering sleep, the BOD is disabled after the MCU has entered the sleep mode, and enabled to verify that the power supply is sufficient before the MCU is allowed to wake from sleep. If the power supply is not sufficient, the MCU will enter a reset mode before any code execution takes place. While in sleep mode, the only critical parameters to handle are the RAM and register contents. On AVR microcontrollers these contents are valid until ~0.3V Vcc, while the AVR microcontroller’s Power-on Reset (POR) triggers at ~1.0V. If a power supply voltage drop should occur while in sleep mode with the BOD disabled, the SRAM and register contents will be valid until a POR occurs. A POR will enable the BOD again and set the POR flag to be read by the application firmware.
The BOD disable feature completely eliminates any power consumption penalty for the BOD during sleep mode and the MCU has full protection in active mode.