Dual-rail LDO with fixed 3.3V and 1.8V outputs
The Texas Instruments TPS70451PWP is a dual-output linear regulator that delivers fixed 3.3V on channel one and 1.8V on channel two, with a combined output current capability of 1A and 2A respectively.
PSRR is 65 dB at 1 kHz on the 1A channel and 60 dB at 1 kHz on the 2A channel — this is the rejection ratio for ripple coming from a switching preregulator. If your 5V rail has 100 mV p-p of 1 kHz switching noise, the 3.3V output will see roughly 56 µV p-p on the 1A rail and 100 µV p-p on the 2A rail. Dropout voltage is 250 mV max at 1A, so the input rail needs at least 3.55V to keep the 3.3V output in regulation under full load.
Protection and control features for a clean start-up
The TPS70451PWP includes Enable, Power Good, Reset, and Sequencing control pins — these let you sequence the two rails on power-up and monitor them during operation. Protection covers Over Current, Over Temperature, Reverse Polarity, and Under Voltage Lockout (UVLO).