SLYY203B September 2021 – April 2023 BQ25125 , LM5123-Q1 , LMR43610 , LMR43610-Q1 , LMR43620 , LMR43620-Q1 , TPS22916 , TPS3840 , TPS62840 , TPS63900 , TPS7A02
IQ is the amount of current used when the integrated circuit (IC) is enabled but not switching nor supporting an external load current. Shutdown current (ISHDN) is the current drawn from the supply when the device is disabled.
The IQ of always-on functions such as power regulators contribute to the overall IQ of systems with long standby times. Inside the power regulators themselves, the voltage reference, error amplifier, output voltage divider and protection circuits all have their own operating currents.
To determine the total IQ drawn from a battery or power supply, you must consider the always-on functions and leakage sources from capacitors, resistors and inductors.
For the IQ of switching converters, some distinctions must be made. Switching converters usually include a power-save mode that enables a longer non-switching period, thereby reducing average IQ. But because the IQ does not include switching currents or the efficiency component of currents drawn from the voltage output (VOUT), like in the example of a boost converter in Figure 4, Equation 1 can be used to calculate a superset of the input-referred no-load operating currents for almost any regulator as:
Currents and voltages are explained in Figure 4, where:
If you know the battery capacity and have calculated the input-referred standby current, Equation 2 estimates the battery life for a heavily duty-cycled low-power system in standby mode >99.9% of the time as:
For example, the battery of a duty-cycled system with 1.2 µA of standby current can last as 8.7 years on a 100-mAh coin-cell battery.