This part is a kind of semiconductor called AX3111.

Function of this product has PWM Control 3A Step-Down Converter.

Manufacturers : AXElite

Image and pinout :

Some of the text within the PDF file :

AX3111 PWM Control 3A Step-Down Converter  GENERAL DESCRIPTION AX3111 consists of step-down switching regulator with PWM control. These devise include a reference voltage source, oscillation circuit, error amplifier, internal PMOS and etc. AX3111 provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to the duty ratio linearly form 0 up to 100%. This converter is build out soft start function that prevents overshoot and inrush current at startup. An over current protect function and short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced. The operating frequency is decided by outside resistance. An external compensation is easily to system stable; the low ESR outp [ ... ]

AX3111 PDF Datasheet Download