The LM1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current.
The device can drive two, three or four LEDs in series from a Li-Ion cell.
Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The output capacitor can be as small as 0.22µF, saving space versus alternative solutions. A low 95mV feedback voltage minimizes power loss for better efficiency.