Supercapacitor charger

Linear Technology has introduced the LTC3225, an inductorless programmable supercapacitor charger for addressing high peak power and battery backup needs in portable applications.

The device employs a low-noise charge-pump architecture to charge two supercapacitors in series to a fixed output (4.8/5.3 V selectable) from a 2.8 to 5.5 V input supply. Charge current is resistor programmable up to 150 mA and the device’s automatic cell balancing feature maintains equal voltages on both cells (2.4/2.65 V selectable) without requiring balancing resistors.

This protects each supercapacitor from overvoltage damage caused by mismatches in cell capacitance or leakage while minimising current drain on the capacitors. The device will not discharge the supercapacitors when the input supply is removed or shorted to ground.

The charger operates with a low 20 µa quiescent current when the output voltage is in regulation and draws 2 µA from V_OUT. Current is further reduced when the input supply is removed as the IC automatically enters a low current shutdown state, drawing less than 1 µA from the supercapacitors.

The basic charging circuit requires only three external components and takes up little space.