The TCR5BM12,L3F is a 500 mA LDO from Toshiba's TCR5BM series, delivering a fixed 1.2 V output from an input up to 5.5 V. The headline spec is the 98 dB PSRR at 1 kHz — that means the output rejects switching ripple from a buck converter or a digital rail by nearly four orders of magnitude. If your 1.2 V rail feeds an ADC reference or a PLL supply, this LDO keeps the noise floor low enough that the converter's own quantization noise, not the supply, sets the SNR.
Dropout and quiescent — the board-level tradeoffs
Dropout is 0.15 V maximum at the full 500 mA load. If the input rail is 1.35 V (a 1.8 V rail through a series diode, for example), the output holds regulation. Below that headroom, the output tracks the input minus dropout — the datasheet's absolute-max table is the boundary, not a suggestion. Quiescent current is 36 µA typical, so the LDO's own draw is negligible in a battery-powered sensor node that sleeps most of the time.
Package and thermal — the exposed pad is not optional
The 4-XDFN exposed-pad package measures 1.2x1.2 mm (5-DFNB). The datasheet's layout recommendation shows a via array under the pad to the inner ground layer. The enable pin and current-limit control are both accessible; tie the enable high if the rail is always on.