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.
Pulse Current Voltage Delay
Meaning
Delay in the recovery of battery voltage after the sudden initiation of a high-current load pulse is a common phenomenon in chemistry-dependent power cells. This pulse current voltage delay occurs when a protective passivation layer has formed on the battery anode, temporarily increasing internal resistance. If the voltage drops below the operating threshold of the microcontroller before the layer is broken down, the system will reset.
Passivation Layer
Lithium chemistry batteries develop a thin film of lithium chloride on the anode during long periods of inactivity, which prevents self-discharge but also increases initial impedance. When the radio initiates a transmission, the sudden demand causes a rapid voltage drop. The pulse current voltage delay is the time it takes for this chemical film to dissolve under the influence of the current flow, allowing the voltage to return to its nominal level.
This delay can range from milliseconds to several seconds depending on the age and temperature of the cell.
Hardware Mitigation
Designers use parallel supercapacitors or large capacitor banks to supply the necessary current during the delay period. These components hold enough charge to run the system during the initial drop, shielding the battery from the peak demand. This design ensures the device remains powered while the passivation layer is cleared.
Testing Protocol
Verifying the battery behavior requires test setups that can simulate the load pulses of the actual radio module after simulated storage periods. Special profiles are applied to recreate the passivation effect before the pulse is drawn. This allows engineers to measure the duration and depth of the voltage dip.