This part is a kind of semiconductor called BAS4.

Function of this product has SCHOTTKY array SERIES.

Manufacturers : Microsemi Corporation

Image and pinout :

Some of the text within the PDF file :

BAS40 8700 E. Thomas Road Scottsdale, AZ 85251 Tel: (480) 941-6300 Fax: (480) 947-1503 and BAS70 SCHOTTKYarray™ SERIES DESCRIPTION Various configurations of Schottky barrier's diodes in SOT-23 packages are provided for general-purpose use in high-speed switching, mixers and detector applications. They may also be used for signal terminations at the board level. This helps maintain signal integrity and counteract the transmission-line effects with (PC) board traces by clamping over/and undershoot from signal reflections with the schottky-low-threshold voltages. This type of termination also does not depend on matching the transmission line characteristic impedance, making it particularly useful where line impedance is unknown or a variable. This method of termination can control distor [ ... ]

BAS4 PDF Datasheet Download