This reference design from Maxim is a current controlled boost driver designed for long strings of LEDs. Driving many LEDs in series has advantages over driving them in parallel. In a parallel configuration each LED will need it’s own current limiting resistor or current control, while the series LEDs make use of a single current controlled power supply. The driver must support the combined voltage of all the LEDs in the string. The reference design can supply up to 100 volts, which translates to around 30 LEDs.