View aic1647 datasheet:

 AIC1647 White LED Step-Up Converter in SOT23 FEATURES DESCRIPTION AIC1647 is a fixed frequency step-up DC/DC 1.2MHz Fixed Frequency Current-Mode PWM Operation. converter designed to drive white LEDs with a Efficiency Up to 84% at VIN=4.2V, 3LEDs, constant current to provide backlight in hand- ILED=20mA held devices. Series connection of the LEDs Drives Up to 6LEDs in series provides identical LED currents resulting in Low Supply Current: 70µA uniform brightness. This configuration eliminates Matches LED Current the need for ballast resistors. Low 95mV Require Tiny Inductors and Capacitors feedback voltage minimizes power loss in the Tiny SOT23-5 Package current setting resistor for better efficiency. AIC1647 is a