A TO-220-3 case is used for packaging. As you can see, the IC chip has 3 terminations. It is important to note that this device has a FIXED POSITIVE SINGLE OUTPUT LDO REGULATOR regulator type. In general, this IC voltage regulator is able to output 3.3V volts on a system basis.
LMS1585AIT-3.3 Features
LMS1585AIT-3.3 Applications
There are a lot of National Semiconductor LMS1585AIT-3.3 Linear Voltage Regulators applications.