12 V rail, 400 mA ceiling — what the ratings mean
The LM2937IMPX-12 is a fixed 12 V output positive voltage regulator from the LM2937 family, rated for 400 mA continuous output current. The fixed output eliminates the need for external resistor dividers — connect the input, ground, and output pins, and the rail is set. Maximum input voltage is 26 V, so budget at least 2–3 V headroom above 12 V for dropout and line transient margin.
Dropout and quiescent — the design budget
Maximum dropout is 1 V at 50 mA load — this is a standard NPN regulator topology, not an LDO. At full 400 mA the dropout will be higher; the datasheet curve (page 7) shows the typical increase. Quiescent current is 2 mA typical, with a 20 mA supply maximum — the Iq is drawn from the input rail regardless of load, so factor it into the input power budget. Protection features include over-temperature shutdown, reverse polarity protection, and short-circuit current limiting. These are built in — no external clamp diodes or foldback circuits needed for basic robustness in an automotive or industrial auxiliary rail.
Obsolete — sourcing via independent distribution
Package and footprint — SOT-223-4
Supplied in a SOT-223-4 surface-mount package (also listed as TO-261-4, TO-261AA). The 12 V fixed output at 400 mA suits auxiliary bias rails for op-amp supplies, relay coils, or sensor interfaces in those temperature ranges.