Battery life is a system promise, and the microcontroller sits at the center of it. Choosing an MCU for a battery-powered or energy-harvesting product is less about MIPS and more about how intelligently the device sleeps, wakes, and offloads work.
Start with the Duty Cycle
Calculate average current first. A sensor node sampling once per minute spends 99.9% of its life asleep: with a 5 mA active current and 2 µs of work, the active contribution is negligible and sleep current dominates. Reverse the picture for a node streaming continuously — then active-mode efficiency and radio power dominate. The classic mistake: optimizing active current on a design whose sleep floor is 50 µA from a poorly chosen regulator or pull-up, wiping out every other gain.
Sleep Modes Are Not All Equal
Compare MCUs by what survives in each sleep state:
- Deep sleep / shutdown (sub-µA): RAM contents may be lost; wake via reset or a few retained words.
- Standby / stop (1–10 µA): SRAM and register state retained, RTC running, wake sources active (GPIO, comparators, periodic timers).
- Peripheral autonomous operation: the real differentiator — ADCs that sample and DMA data to RAM, comparators that filter wake events, all while the CPU sleeps. Every wakeup you avoid is a factor-of-10 saving on the energy budget.
Wake-Up Latency and the Hidden Costs
A 5 µs wake-up sounds free, but add oscillator restart, PLL lock, and software initialization, and real wake time can reach hundreds of microseconds or milliseconds. During that window the core may draw full active current. Check the vendor's measured wake-up energy, not just the headline latency.
Architecture and Ecosystem Matter Too
- Process and voltage scaling: modern MCUs offer per-core DVFS and separate power domains — shut down domains you do not use.
- Flash vs FRAM: FRAM-based MCUs write logs in sleep-friendly bursts without the erase-charge overhead of flash.
- Toolchain and drivers: low-power features only deliver if your firmware actually uses them. Mature low-energy libraries (tickless RTOS idle, DMA-driven peripherals) shorten the path.
- Supply voltage range: running directly from a Li-SOCl2 cell (3.6 V) or a single coin cell changes which parts qualify.
A Shortlist Workflow
Filter by sleep current with retention, wake sources matching your sensors, and the analog peripherals you need on-chip; then prototype the actual duty cycle and measure µA on hardware — datasheet tables assume ideal firmware.
Sourcing Low-Power MCUs
We stock low-power microcontrollers and their supporting analog components, including MSP430-series parts and other hard-to-find MCUs. Check the catalog or send us your part list for pricing and lead time.
