Linear Technology has a charger IC for 2-cell supercapacitors.

The LTC4425 employs a linear CC-CV architecture with thermal limiting to charge two supercapacitors in series to a programmable output voltage from a Li-Ion/Polymer battery, a USB port, or other 2.7V to 5.5V current-limited supply.

It features two operating modes: charge current profile (normal) mode and LDO mode.

The device’s charge current profile mode charges the top of the supercap stack to the input voltage V(in) with a charge current that varies inversely with the input-to-output voltage differential in order to present excessive heating.

The LDO mode charges the stack to an externally programmed output voltage with a fixed charge current that is also externally programmable.

Charge current is resistor programmable up to 2A (3A peak), and each capacitor is protected against overvoltage by internal shunts (2.45V/2.7V selectable).

The LTC4425’s onboard current-limited diode has a 50mohm on-resistance to prevent back-driving of V(in).