Switched-capacitor charge pumps, which offer a size advantage over the equivalent inductor-based regulator, are popular for boosting the battery voltage in small handheld equipment. As an example, the subscriber identification module (SIM) in European cellular phones requires a regulated 5 V for powering low-current loads. One such circuit employs two tiny SOT-22 ICs and three surface-mount capacitors to double and postregulate the voltage of a single lithium-ion battery.
It delivers 15 mA from a 2.7-V minimum output voltage.
Battery voltage is boosted by a charge-pump voltage doubler with a 2-V to 5.5-V input range (IC1) and is stepped down to the desired level by a micropower linear regulator (IC2). As the battery discharges, the system compensates declining voltage with an increase in efficiency, reaching 84 percent at 2.5 V. Because the SIM and other smart cards are used only a few times a day and for less than a second each time, one can sacrifice some efficiency for smaller size and lower cost. The circuit's low quiescent current ranges from 60 microamps at 2.6 V to 80 microamps at 3.6 V.
See related chart