Meaning
Transient voltage reduction occurs when a high load demand exceeds the immediate delivery capacity of a power supply or battery system. Electrical engineering defines pulse current sag as the difference between the nominal supply voltage and the minimum voltage during a load event. This drop is a function of the discharge rate and the age of the power source.
Protective circuits must account for this behavior to avoid system brownouts.
Voltage Deviation
Magnitude of the drop depends on the magnitude of the current pulse and the series resistance of the energy source. During a pulse current sag, the supply voltage may fall below the operational limit of the cellular modem. This phenomenon is most frequent in lithium thionyl chloride batteries during high power transmission.
Circuit designers must account for this drop when defining the minimum operating voltage.
Source Resistance
Electrochemical properties and aging increase the internal impedance of the battery cells. A higher source resistance directly correlates to a more severe pulse current sag during operation.
Recovery Profile
Potential levels return to the nominal value once the high current demand ceases. The specific duration of a pulse current sag depends on the chemistry of the cell.
