This part is a kind of semiconductor called ACT4088.

Function of this product has 1.4MHz Step-Down DC/DC Converter.

Manufacturers : Active-Semi

Image and pinout :

Some of the text within the PDF file :

Rev PrA, 24-Jul-07 Advanced Product Information – All Information Subject to Change ACT4088 28V, 1.5A, 1.4MHz Step-Down DC/DC Converter in SOT23-6 FEATURES            Wide 4.5V to 28V Input Voltage Range 1.5A Output Current (12VIN to 5VOUT) Output Adjustable Down to 0.81V 0.3Ω Internal Power MOSFET Up to 92% Efficiency Stable with Low ESR Ceramic Output Capacitors Fixed 1.4MHz Operating Frequency Internal Soft-Start Function Over Current Protection with Hiccup-Mode Thermal Shutdown Available in a SOT23-6 Package GENERAL DESCRIPTION The ACT4088 is a current-mode step-down DC/DC converter that supplies up to 1.5A into 5V from a 12V input. 1.4MHz switching frequency allows the use of tiny external components, and internal loop compensation provides simpl [ ... ]

ACT4088 PDF Datasheet Download