Cellular Internet of Things Power Budget Management Principles
Cellular IoT power management matches PSM and eDRX timers to application frequency while decoupling peak pulse currents from battery internal resistance.
Peak Transmission Current
Meaning
Maximum instantaneous power consumption occurs during the highest intensity phase of an uplink radio operation. The peak transmission current defines the electrical load that the power delivery network must support without falling below the minimum operating voltage. This value is considerably higher than the average current consumed during the rest of the operational cycle.
Antenna impedance and output power settings directly influence the magnitude of this demand.
Power Supply
Regulators and converters must be sized to handle the maximum load without overheating or losing efficiency. Choosing a component that is too small leads to excessive heat and potential failure during long transmission cycles. The peak transmission current is the primary factor in determining the inductor rating for a switching power supply.
Voltage Sag
Internal resistance in the battery causes a drop in output voltage when the load increases. If the peak transmission current is high enough, the voltage might fall below the system cutoff level. This sag is most pronounced at cold temperatures where chemical reactions are slower.
Signal Configuration
Radio parameters such as modulation type and antenna gain impact the amount of current needed for a successful link. High gain antennas reduce the power needed from the amplifier, which in turn lowers the demand on the battery. Software can be used to limit the output power in areas with strong network coverage to conserve energy.
It is also possible to schedule transmissions for times when the battery voltage is at its highest point in the discharge cycle. Software can be used to limit the output power in areas with strong network coverage to conserve energy.