This part is a kind of semiconductor called D1703L.
Function of this product has N-CHANNEL MOSFET.
Manufacturers : STMicroelectronics
Image and pinout :

Some of the text within the PDF file :
STD1703L N-CHANNEL 30V - 0.038Ω - 17A - DPAK STripFET™ II MOSFET TYPE STD1703L s s VDSS 30 V RDS(on) <0.05 Ω ID 17 A TYPICAL RDS(on) = 0.038 Ω APPLICATION ORIENTED CHARACTERIZATION 3 1 DPAK DESCRIPTION This MOSFET is the latest development of STMicroelectronics unique “Single Feature Size™” strip-based process. The resulting transistor shows extremely high packing density for low onresistance, rugged avalance characteristics and less critical alignment steps therefore a remarkable manufacturing reproducibility. INTERNAL SCHEMATIC DIAGRAM APPLICATIONS s DC-DC CONVERTERS s LINEAR POST REGULATION ORDERING INFORMATION SALES TYPE STD1703LT4 MARKING D1703L PACKAGE DPAK PACKAGING TAPE & REEL April 2004 1/10 STD1703L ABSOLUTE MAXIMUM RATINGS Symbol [ ... ]
D1703L PDF Datasheet Download
