It comes in a D2PAK (TO-263) surface-mount package, making it suitable for high-density power supplies, OR-ing diodes in redundant systems, and output rectification in switch-mode converters up to several hundred watts. The 920 mV forward voltage at 20 A is typical for a 170 V Schottky — expect higher conduction loss than a lower-voltage Schottky but better reverse-recovery than a fast-recovery silicon diode.
ST lists the STPS40170CG as obsolete. That means no further factory orders are accepted — no last-time-buy window remains open. Date codes will vary, and counterfeits are a real risk on a discontinued high-current Schottky. A visual inspection and electrical test against the datasheet limits are standard practice before these go into a production board.
170 V Schottky — where the ratings matter
The 170 V Vr rating gives about 15% derating margin for a 48 V or 72 V bus, but it is tight for a 120 V DC rail — you are at the edge of the SOA. The 20 A per diode is the average rectified current, not the surge; peak repetitive current depends on the junction temperature and the thermal resistance of the D2PAK footprint.