Energy-saving MCU

Power consumption in CMOS ICs is broadly classified as dynamic power in an operating circuit, such as switching and static power, an example being leakage which is measured any time a circuit is powered on.

Traditionally, static power consumes less energy than dynamic power, yet as CMOS geometries continue to shrink, static power is becoming a larger portion of the total energy used.

Power-saving technologies, therefore, must address both forms of power consumption.

The Freescale ColdFire V1 MCF51QE128 (32-bit), available from Farnell, is a member of the Flexis series of MCUs that has extreme energy efficiency with ultra-long battery life in portable applications, using deep sleep modes.

Each device has multiple stages of stop modes in addition to new low-power wait and low-power run modes, each adding energy savings.

The low-power wait and low-power run modes allow the device to operate in a low-power mode with all peripherals enabled.

Additionally, its ultra-low-power 32 kHz external oscillator consumes less than 1 µA and can be used in all modes. Normally, in run mode an IC has to run at a frequency of at least 1 MHz.

Cycling through sleep and wake-up modes to monitor system needs and events can add to peak energy consumption (clock trees can consume as much as 40% of the IC’s active power).

Alternatively, the devices use a 32 kHz oscillator which has a low run current and avoids the current spikes normally experienced each time the mode is changed.

The devices are manufactured using a low-voltage low-power (LVLP) process, using transistors with an increased channel length to reduce leakage current, which decreases static power consumption. The standard cell library has also been optimised, and includes a number of low-power elements including a peripheral clock gating register that can disable clocks to unused modules as well as the 32 kHz external oscillator that provides an accurate clock source to the real-time counter module.