This part is a kind of semiconductor called AP3407A.

Function of this product has 1.4MHZ HIGH EFFICIENCY SYNCHRONOUS DC-DC BUCK CONVERTER.

Manufacturers : Diodes

Image and pinout :

Some of the text within the PDF file :

AP3407/A 1.2A, 1.4MHZ HIGH EFFICIENCY SYNCHRONOUS DC-DC BUCK CONVERTER Description The AP3407/A is a 1.4MHz fixed frequency, current mode, PWM synchronous buck (step-down) DC-DC converter, capable of driving a 1.2A load with high efficiency, excellent line and load regulation. The device integrates synchronous P-channel and N-channel power MOSFET switches with low on-resistance. It is ideal for powering portable equipment that runs from a single Li-ion battery. A standard series of inductors are available from several different manufacturers optimized for use with the AP3407/A. This feature greatly simplifies the design of switch-mode power supplies. The AP3407/A is available in SOT-23-5. Features  Input Voltage Range: 2.5V to 5.5V  Output Voltage: 0.6V to VIN  ADJ Output  Fix [ ... ]

AP3407A PDF Datasheet Download