SOT-89-3 package and board-fit
The BD54FA1FP3-ZTL comes in a SOT-89-3 (TO-243AA) surface-mount package — a three-lead power package with a large collector tab on the back that doubles as the thermal path. The tab is tied to ground (output is positive), so the PCB copper area under the tab sets the junction-to-ambient thermal resistance. For 100 mA output at 3 V dropout, that's 300 mW to sink; a 1 cm² copper pour on the bottom layer keeps the die below the 85 °C ambient ceiling. Pin 1 is the leftmost lead when the package is viewed with the tab facing away — standard SOT-89 orientation. The tab is electrically connected to ground, so no isolation pad is needed, but the solder paste coverage on the tab should be about 50% to avoid voiding under reflow.
5.4 V fixed output — what the rail needs
Output is fixed at 5.4 V with a positive configuration and a single regulator on die. That 5.4 V rail is non-adjustable — the internal resistor divider is laser-trimmed. The input must stay at least 3 V above the output at full load (dropout max 3 V at 100 mA), so the minimum input rail is 8.4 V when sourcing 100 mA. At lighter loads the dropout drops, but the headroom design should budget for the worst case. The 450 µA quiescent current (Iq) is the regulator's own draw — at 100 mA output that's 0.45 % overhead, acceptable for always-on rails. In a battery-powered system drawing 1 mA average load, that same 450 µA Iq becomes a significant drain; a load-switch to disconnect the regulator when idle would help.
Protection features and operating range
On-chip protection includes over-current limiting, thermal shutdown, and soft-start. The over-current limit folds back the output current during a short — the part survives a hard short indefinitely without damage, though the die temperature will rise until the thermal shutdown triggers. Soft-start limits inrush current on power-up, which matters when the output capacitor is large (10 µF or more) and the input supply is weak. Temperature range is -25 °C to 85 °C ambient — industrial grade, not automotive. For an engine-bay or under-hood application this part is out of spec; for a factory-floor sensor or control cabinet it is fine.
Active production and compliance
Available in Tape & Reel (TR) for automated assembly, or Cut Tape (CT) for prototype and low-volume builds.