STM32 Low-Power Modes

The STM32L series can achieve sub-1uA sleep current. Here's what actually matters in practice.

Stop Mode 2 on the STM32L0 shuts down most clocks while keeping the RTC and a few wakeup sources active. The datasheet says 0.4uA typical. In practice, measured on a bare chip with all unused GPIOs configured as analog inputs (important — floating digital inputs draw leakage current), I measured 0.6uA. The most common reason for higher than expected current is floating inputs or unused pins left in output mode.

Wake latency from Stop Mode 2 is about 1ms to MSI clock ready. If your application needs fast wake latency, Stop Mode 1 is faster but draws more. For a sensor node waking every 5 minutes, 1ms latency is invisible. Power consumption calculation for a 5-minute wake cycle with 100ms active time at 3mA and 4min 59.9s at 0.6uA gives an average of about 1uA — meaning years of life on a coin cell.