Schottky 40V, 300mA — the rail-protection workhorse
The STMicroelectronics BAT54KFILM is a Schottky barrier rectifier rated for 40 V reverse voltage and 300 mA average forward current, housed in the compact SOD-523 surface-mount package.
5 ns reverse recovery — fast enough for line-frequency rectification
Junction capacitance measures 10 pF at 1 V reverse bias and 1 MHz, low enough to avoid signal degradation in low-speed clamping or protection circuits.
SOD-523 footprint — the smallest BAT54 variant
The SOD-523 body (1.6 x 0.8 mm nominal) is the smallest package in the BAT54 family, about half the board area of the SOT-23 version. The land pattern must match the SOD-523 pad geometry — a SOT-23 footprint will not fit. Reverse leakage is specified at 1 µA maximum at 30 V reverse bias and 25°C junction; leakage doubles roughly every 10°C rise, so at 125°C junction the leakage current can exceed the forward conduction in a lightly loaded circuit.