This part is a kind of semiconductor called PT4101B23F.
Function of this product has White LED Step-Up Converter.
Manufacturers : Powtech
Image and pinout :
Some of the text within the PDF file :
PT4101 White LED Step-Up Converter GENERAL DESCRIPTION The PT4101 is a step-up DC/DC converter designed for driving up to 5 white LEDs in series from a single cell Lithium Ion battery with constant current. Because it directly regulates output current, the PT4101 is ideal for driving light emitting diodes (LEDs) whose light intensity is proportional to the current passing through them, not the voltage across their terminals. A single external resistor sets LED current between 2mA and 20mA, which can then be easily adjusted using either a DC voltage or a pulse width modulated (PWM) signal up to 100KHz. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over-voltage condition is present due to an [ ... ]