Fixed 5V LDO with 68 dB PSRR — the noise-sensitive rail choice
The L4940D2M5-TR from STMicroelectronics is a fixed 5 V positive-output LDO regulator delivering up to 1.5 A.
Dropout and thermal — the real-world headroom numbers
Maximum dropout voltage is 0.9 V at 1.5 A load, so the input rail must stay above 5.9 V worst-case to maintain regulation.
Protection and temperature range
On-chip protection covers over-temperature, reverse polarity, and short circuit — three failure modes that kill unguarded regulators in field returns.
Obsolete — sourcing the L4940D2M5-TR today
STMicroelectronics lists the L4940D2M5-TR as obsolete. No direct successor or pin-compatible second source is recorded in the official documentation.
Housed in a D2PAK (TO-263-3) surface-mount package with two leads and a tab — the tab is the ground path and primary heat sink. The exposed copper pad on the PCB must be sized for the 1.5 A load and the junction-to-ambient thermal resistance; a 2 oz copper pour under the tab is the usual starting point.