EFM32™ 32-bit MCU Ultra Efficient Energy Modes

With a high performance ARM® Cortex®-M processor, high code density and autonomous peripherals, the EFM32™ 32-bit microcontroller (MCU) executes application code faster than 8-, 16- and even 32-bit solutions. Because of this, the EFM32 can spend most of its time in some of the ultra efficient energy saving modes that it features. Several energy modes are available to reduce power consumption. EFM32 MCUs are designed to achieve a high degree of autonomous operation in low energy modes. An intelligent combination of peripherals, low-leakage RAM with data retention, DMA and interconnection ability, low-power oscillators and very short wake-up times makes it possible to remain in the low energy modes for long periods of time to reduce energy consumption.

Energy Mode 0 — Active/Run Mode

High performance CPU and peripherals designed for ultra-low power operation

In Energy Mode 0 (EM0) the ARM Cortex-M CPU fetches and executes instructions from flash or RAM, and all low energy peripherals can be enabled. Due to its high processing power, the EFM32 can quickly enter one of the low energy modes from EM0 effectively halting the CPU and flash memory. After a wake up, all low energy modes return to EM0 within 2 µs, making it easy to enter the low energy mode and return to the high 32-bit performance when needed.

Power consumption in EM0: 180 µA/MHz

Energy Mode 1 — Sleep Mode

Stay in low energy modes while performing advanced tasks

In Energy Mode 1 (EM1) the clock to the CPU is disabled, effectively reducing the energy needed for operation while maintaining all low energy peripheral (including flash and RAM) functionality. By using the peripheral reflex system (PRS) and DMA, the system can collect and output peripheral data without CPU intervention. This autonomous behavior enables the system to remain in EM1 for long periods of time, thereby increasing battery life. Additionally, the low-leakage RAM ensures full data retention.

Power consumption in EM1: 45 µA/MHz

Energy Mode 2 — Deep Sleep Mode

Advanced low power and autonomous operation without CPU intervention

In Energy Mode 2 (EM2), the EFM32 microcontrollers offer a high degree of autonomous operation while keeping energy consumption low. The high frequency oscillator is turned off in EM2; however, a 32 kHz oscillator and the real time clock are available for the low energy peripherals. Since the ARM Cortex-M CPU is not running in EM2, the MCU performs advanced operations in sleep mode. The peripherals run autonomously due to intelligent interconnection of the modules and memory, the wake-up time to EM0 is only 2 µs and low-leakage RAM ensures full data retention in EM2.

Power consumption in EM2: 0.9 µA

Energy Mode 3 — Stop Mode

Operation, full RAM rentention and short 2 µs wake-up from interrupts

Energy Mode 3 (EM3) tailors the energy consumption of the EFM32 to maintain a very short wake-up time and respond to external interrupts. In EM3 the low-frequency oscillator is disabled, but the low-leakage RAM ensures full data retention and the low power analog comparator or asynchronous external interrupts can wake-up the device.

Power consumption in EM3: 0.6 µA

Energy Mode 4 — Shutoff Mode

For applications that don't need RTC or RAM retention

In Energy Mode 4 (EM4) – the deepest energy mode available – the EFM32 MCU is completely shut down and the only way to wake up is with a reset. This energy mode enables further energy savings for applications that do not require a RTC or RAM retention. Energy Mode 4 is available in select low energy peripherals, including:

  • Power-on reset
  • External interrupts

Power consumption in EM4: 20 nA

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