What the 75 dB PSRR means for your rail
The TLV1117-18IDCYR is a fixed 1.8 V LDO from the TLV1117 family, rated for 800 mA continuous output. Its headline spec is 75 dB of power-supply rejection at 120 Hz — the ripple frequency from a full-wave rectified mains supply. That means the output sees roughly one ten-thousandth of the input ripple at that frequency, which is enough to keep a sensitive analog front-end (ADC reference, op-amp supply, sensor bias) clean in a mixed-signal design running off a lightly filtered DC rail.
Dropout headroom and thermal budget
Maximum dropout is 1.3 V at the full 800 mA load. Below that headroom the output falls out of regulation.