32 MHz Cortex-M0+ with 16 KB Flash — the power-conscious BOM fit
The 32-LQFP package (7x7 mm) with 28 I/O lines provides enough GPIO for sensor interfaces, keypads, and small displays while keeping board area tight.
The base product number is STM32L021, and the series (STM32L0) is a mature, widely deployed platform with long-term supply commitment from ST.
The 1.65 V minimum supply is the key enabler for single-cell alkaline (1.5 V nominal) or LiFePO4 (1.65 V fully charged) operation without a boost converter. At the 3.6 V upper end, it tolerates a fully charged Li-ion cell (4.2 V) only if a series diode or regulator drops the voltage — the absolute maximum is 3.6 V, so a direct 4.2 V connection is outside the rated range.
Memory sizing — 16 KB Flash, 2 KB SRAM, 512 B EEPROM
The 16 KB Flash is sized for small firmware images — bootloader, sensor driver, communication stack, and a modest application loop. The 2 KB SRAM limits data buffers and stack depth; designs with large frame buffers or multi-packet serial queues should budget carefully. The 512-byte EEPROM (organized as 512 x 8) is useful for calibration constants, configuration parameters, and fault logs that survive power loss without external EEPROM — saving a package and a serial bus.
32-LQFP package — footprint and rework notes
The 0.8 mm pitch is forgiving for inspection and touch-up. The supplier device package is 32-LQFP (7x7).