Trade-Offs in the Sleep Mode Management of the RP2040 Microcontroller

Optimizing energy efficiency in microcontrollerbased IoT systems requires careful management of sleep modes to balance energy savings with application-specific timing constraints. This study analyzes the trade-offs between the available sleep modes in the RP2040 microcontroller-either utilizing an external crystal clock or an internal ring-oscillator-across varying core supply voltages $(0.85-1.30 ~\mathrm{V})$ and operating frequencies $(140-416 \text{MHz})$. The crystal-clock mode enables faster wakeup times (sub-millisecond range) drawing higher sleep currents compared to the ring-oscillator mode, which minimizes idle power but incurs longer wake-up delays. A critical break-even time $\mathbf{T}_{E Q}$ is identified, beyond which the ring-oscillator's lower sleep current outweighs its wake-up energy penalty making it advantageous for longer sleep intervals. This timing threshold displays a strong influence on core supply voltage shifting to longer durations with supply voltage increase, while temperature variations exhibit negligible impact. The findings of this work provide a framework for aligning sleep strategies with idle durations and timing constraints, making it particularly useful for optimizing energy consumption in IoT applications with varying duty cycles, such as sensor networks or wearable devices.