Calculating Low Power Wide Area Network End Node Battery Longevity
LPWAN end node longevity relies on dynamic state-machine energy integration multiplied by chemical passivation and thermal capacity derating factors.
Thermal Capacity Derating
Meaning
Systematic reduction of the maximum allowable power or current limits of a component based on the operating temperature of its environment prevents thermal runaway and component failure. This thermal capacity derating is necessary because the ability of a semiconductor or passives to dissipate heat decreases as the ambient temperature rises. Implementing this reduction ensures that the internal junction temperatures of the device remain within safe limits under all operating conditions.
Thermal Impedance
Heat transfer from the component junction to the surrounding air depends on the thermal resistance of the package and the printed circuit board. When operating in warm environments, the temperature gradient is smaller, which reduces the rate of heat dissipation. To compensate for this, thermal capacity derating curves are used to adjust the maximum operating current of power regulators and transceivers.
This adjustment prevents localized overheating and extends the lifespan of the hardware.
Reliability Benefit
Operating components below their absolute maximum limits at elevated temperatures reduces the rate of thermal degradation. This practice prevents early failure of the power management circuits and radio amplifiers.
Enclosure Design
Placing the electronic assembly inside a sealed, compact enclosure restricts airflow and increases the internal temperature during operation. Developers must use the derated component specifications when calculating the thermal budget of the entire assembly. This ensures that the closed system can operate continuously without experiencing thermal shutdown or performance degradation.