The BAT54ZFILM is a Schottky barrier diode from STMicroelectronics, rated for 40 V DC reverse voltage and 300 mA average rectified current. Its 5 ns reverse recovery time places it in the fast-switching class, suitable for high-frequency rectification, freewheeling, and clamping in low-power DC-DC converters, polarity protection, and signal conditioning circuits.
Obsolete — sourcing reality and the replacement path
marks the BAT54ZFILM as Obsolete. This means ST has stopped production; no last-time-buy window remains. The closest active drop-in replacement for the SOD-123 footprint is the BAT54S series or the BAT54FILM variant, both still listed as current by ST. For BOM continuity, qualifying the BAT54FILM (same SOD-123 case, same electrical ratings) eliminates single-source risk.
SOD-123 footprint — layout and thermal notes
The SOD-123 package is a small outline diode package with a single cathode band. The 10 pF junction capacitance at 1 V is low enough for RF and high-speed switching applications up to several hundred MHz, but the 900 mV forward voltage drop at 100 mA is higher than some low-Vf Schottky types — expect about 0.45 V to 0.5 V at 10 mA, typical for a 40 V Schottky. The 1 µA reverse leakage at 30 V is tight for high-temperature operation; at 125°C junction, leakage can increase 10x, so derate the reverse voltage in hot environments.