25 ns trr — the switching-speed decision
That 25 ns trr is the headline number: it tells you this is a diode built for the output stage of a hard-switched power supply, not a 50/60 Hz line rectifier. The fast recovery cuts turn-off losses in continuous-conduction-mode boost or flyback converters, which is where a standard recovery part would run hot and eat efficiency.
Forward drop and leakage at the operating point
Forward voltage is 3.6 V maximum at 5 A — a typical figure for a fast-recovery diode at that current and voltage class. Reverse leakage is 6 µA at the 600 V rating, measured at 25 °C junction.
Housed in a TO-220AC insulated package (TO-220-2 with the tab electrically isolated), this is a through-hole part. The base number STTH506 covers the non-insulated TO-220AC variant; the 'DTI' suffix flags the insulated version.
No last-time-buy risk or obsolescence concern on the horizon for this part.