Cortex-M0 based MCU takes as little as 55 µA/MHz

The SAM 21L series of MCUs uses a Cortex-M0 core and features low power, 48 MHz operation, up to 256 Kbytes of flash, and 44 Kbytes of SRAM. Operational current is 320 µA at 4 MHz, typical, non-essential peripherals off. Supply range is 1.62 to 3.63 V.

It consumes less than 940 nA with 40 Kbyte SRAM retention, real-time clock, and calendar, and 200 nA in the deepest sleep mode. The IC has a 16-channel DMA, a 12-channel event system, 24- and 16-bit counters, CRC-32, USB 2.0, an AES encryption engine, a 192-channel touch controller, a 20-channel 12-bit A/D converter, dual 12-bit D/A converters, two comparators, and three op-amps.