This part is a kind of semiconductor called FR9809.

Function of this product has 500KHz Synchronous PWM-Buck DC/DC Converter.

Manufacturers : Fiti

Image and pinout :

Some of the text within the PDF file :

fitipower integrated technology lnc. FR9809 21V, 5A, 500KHz Synchronous PWM-Bu8c5kT DC/DC Converter Description FR9809 is a high-efficiency synchronous step-down DC/DC converter that employs a special process technique to obtain very low RDS(ON) for the internal metal–oxide–semiconductor field-effect transistor (MOSFET). The input operation voltage is in a wide range from 4.75V to 21V, and continuous load current capability is 5A. Control circuit is designed by a particular current mode which provides fast transient response and eases loop stabilization. This product has a very low standby current less than 1μA in shutdown mode. When the pin voltage is less than 0.4V, FR9809 will turn off. Fault protection includes over current protection (OCP), under voltage lockout protection (UV [ ... ]

FR9809 PDF Datasheet Download