Sleep Current Arithmetic behind a Five Year Battery Claim
Five-year battery claims require balancing microampere sleep floors, primary cell passivation derating, and protocol airtimes across 43,800 hours.
Sleep Current Arithmetic
Meaning
Mathematical summation of the residual currents drawn by all components in an electronic assembly during its lowest power state defines the baseline discharge rate of the system. Applying sleep current arithmetic allows developers to calculate the total energy lost during the extended inactive periods that separate wireless transmissions. This summation provides the baseline figure upon which the overall operating life of the device is modeled.
Cumulative Summation
Every chip connected to the supply rail contributes to the total leakage and standby current. This includes the quiescent current of the voltage regulators, the leakage of bypass capacitors, and the input bias currents of the microcontroller’s GPIO pins. Summing these values reveals the total inactive drain.
Calculation Example
Consider a device with a regulator drawing two microamperes, a microcontroller in deep sleep drawing one microampere, and a sensor module drawing one microampere of standby current. Adding these values together yields a total sleep drain of four microamperes.
Battery Implications
Multiplying this aggregate current by the total hours spent in the sleep state gives the cumulative sleep energy consumption. This resulting value is compared to the active transmission energy to evaluate the relative impact of each state on battery life. In many remote telemetry applications, the sleep energy exceeds the active transmission energy over the system life.