The input of the LTC3625 can also be driven by many widely available solar cells. In this circuit, MPPT (maximum power point tracking) is implemented by modulating the charge current based on the input voltage of the LTC3625. The LTC3625/LTC3625-1 are programmable supercapacitor chargers designed to charge two supercapacitors in series to a fixed output voltage (4.8V/5.3V or 4V/4.5V selectable) from a 2.7V to 5.5V input supply. Automatic cell balancing prevents overvoltage damage to either supercapacitor while maximizing charge rate. No balancing resistors are required.