Ultra-low-power MCUs, with minimal power consumption and efficient energy management capabilities, are rapidly penetrating fields such as the Internet of Things (IoT), wearables, smart home, and medical electronics. The dynamic power formula PDynamic = f x CL x VDD2 reveals three paths to reduce power: frequency scaling, voltage scaling, and load optimization.
The Three Dimensions of Power Consumption
Static Power (Standby / Sleep Current)
Static power is the current consumed by the MCU in sleep mode, which directly determines the standby time of battery-powered devices. Key metrics of modern ultra-low-power MCUs:
| MCU Model | Core | Sleep Current | Feature |
|---|---|---|---|
| STM32U575 | Cortex-M33 | 8nA | Hardware Crypto Engine |
| MSP430FR5994 | 16-bit RISC | 0.4muA | FRAM Zero Write Power |
| HC32L136 | Cortex-M0+ | 0.5muA | 12-bit 1Msps ADC |
| GD32L233 | Cortex-M23 | 1muA | USB Type-C |
| EFM32PG22 | Cortex-M33 | 2muA | Integrated DC-DC |
Dynamic Power (Running Current / MHz)
Dynamic power reflects the energy efficiency of the MCU in the active state. Key selection parameters include running current (muA/MHz) and actual power consumption at different frequencies. The STM32L4 series consumes as little as 19muA/MHz in run mode, the HC32L series about 30muA/MHz, and domestic MCUs have matched the basic metrics of international giants.
Peripheral Power
Peripheral power is often overlooked, yet it is an important component of total system power. High-power peripherals such as ADC sampling, RF transmission, and LCD driving require independent management strategies: turn off the clock immediately after use, free the CPU to sleep via DMA, and control power to high-power peripherals through enable pins.
Fine-Grained Control of the Power State Machine
The core of low-power design is the fine-grained utilization of the MCU’s various power modes:
| Mode | Wake Source | Data Retention | Recovery Time | Current Draw |
|---|---|---|---|---|
| Active | – | All | – | 1-10mA |
| Sleep | Any Interrupt | All | 1muS | 100muA-1mA |
| Stop | External Event/RTC | SRAM Retained | 10muS | 1-10muA |
| Standby | Reset/Wake Pin | Lost | 1ms | 0.1-1muA |
Selection Recommendations
- Battery-powered devices: Prefer the HC32L136 or MSP430FR series (FRAM wear-resistant write)
- Wireless connectivity needs: Silicon Labs BG22 (international) or GD32W515 (domestic Wi-Fi 6 + BLE 5.2)
- High-security scenarios: Nations Technologies N32L406 (national cryptographic algorithm) or STM32U5 (TrustZone)
- Extreme low cost: HC32L021 or CEC CMS32L051
Domestic MCUs have matched international giants on basic power metrics and hold advantages in price and local support. It is recommended to prioritize evaluating domestic solutions for new projects; complex systems can consider a hybrid architecture of “international MCU as main controller + domestic coprocessor.”
Honchak Electronics provides ready-to-ship supply and selection support for the full range of low-power MCUs such as the STM32L/U series, ESP32 series, HC32L series, and GD32L series. Feel free to contact us for detailed selection solutions.