The STMicroelectronics BAT54SWFILM is a dual Schottky diode array with the two die connected in series inside a single SOT-323 package. It is rated for 40 V reverse voltage and 300 mA average forward current per diode, with a 5 ns reverse recovery time that places it firmly in the fast-switching class. The series configuration means the two diodes share a common cathode node internally — the anode of one and the cathode of the other are the external pins. That topology is useful for voltage clamping, steering, or creating a low-capacitance series string without an extra PCB trace.
5 ns trr — the switching-speed floor
A 5 ns reverse recovery time is the Schottky's natural advantage over a pn-junction diode at this current rating. In a high-speed switching circuit — say a 1 MHz DC-DC converter or a signal-line clamp — the trr determines how cleanly the diode turns off. Below 5 ns the stored charge is negligible, so the switching loss stays low and the waveform edges stay sharp. The forward voltage drop is specified at 900 mV maximum when carrying 100 mA. That is typical for a 40 V Schottky in this current class — the trade-off is a slightly higher Vf than a lower-voltage Schottky, but the 40 V headroom covers 24 V rails and 12 V battery lines with margin.
SOT-323 footprint — board-space constraint
The SOT-323 (SC-70) package occupies roughly 2.0 mm × 2.1 mm of board area. The three pins (anode1, common cathode, anode2) follow the standard pinout for this series-connected dual-Schottky footprint.
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