The FAN5616 generates a regulated output current from a battery with an input voltage between 2.7V to 5.5V. Switch reconfiguration and fractional switching techniques are utilized to achieve high efficiency over the entire input voltage range. The adaptive nature of the built-in charge pump eliminates the need for LED preselection (matching) and ensures operation with high efficiency. The driver's built-in, proprietary, auto-sense circuitry ensures the same high efficiency regardless of the number of LEDs. When the input voltage is sufficiently high to sustain the LED's programmed current level, the FAN5616 reconfigures itself to operate as a linear regulator, and the charge pump is turned off.