80 dB PSRR at 1 kHz — the analog-rail LDO
The Microchip MIC5317-3.3YMT-TR is a single-output, fixed 3.3 V positive LDO rated for 150 mA continuous output. Its headline feature is the PSRR curve: 80 dB at 1 kHz, rolling off to 65 dB at 10 kHz, which puts it in the low-noise regulator class suitable for powering analog front-ends, ADC reference buffers, or RF VCO supplies where the upstream switching regulator needs suppression. Dropout is specified at 0.31 V maximum at the full 150 mA load, so the input rail needs at least 3.61 V to hold regulation. Quiescent current sits at 39 µA typical — not the lowest for battery-idle, but reasonable for a part that prioritises PSRR over micropower.
Thermal and package — 1×1 mm UDFN with exposed pad
The package is a 4-lead UDFN measuring 1×1 mm with an exposed pad. That pad is the primary thermal path: without a via stitch under the pad, the junction temperature climbs quickly above 100 mA continuous at 125°C ambient. The exposed pad also serves as the ground return — the PCB layout must connect it directly to the ground plane with multiple vias to keep inductance low.
Protection and control
An Enable pin lets the system shut down the LDO for power sequencing or sleep modes. On-chip protection includes over-current and over-temperature shutdown. No reverse-current protection is listed, so if the output can rise above the input (e.g., a backup battery), an external Schottky or series diode is needed.