1 A adjustable LDO with 1.25 V dropout
The Texas Instruments LMS8117AMP-ADJ/NOPB is a single-output positive adjustable LDO rated for 1 A continuous output. The maximum dropout voltage is 1.25 V at full load, meaning the input rail must stay at least 1.25 V above the programmed output voltage across the load range to maintain regulation. Output voltage is adjustable from a 1.25 V reference up to 13.8 V maximum, set by an external resistor divider. The 5 mA quiescent current is typical for a 1 A LDO of this generation — budget it into the total load current when calculating efficiency at light load.
Ripple rejection and protection
Power supply rejection ratio is 60 to 75 dB at 120 Hz — this is the ripple frequency after a full-wave rectifier. For a 12 V rail feeding a 5 V output, the 120 Hz ripple is attenuated by a factor of 1000 to 5600, so the output sees less than 1 mV of ripple from a 1 Vpp input ripple. Above 120 Hz the PSRR rolls off; upstream switching noise needs a separate LC filter ahead of the LDO.
The datasheet recommends a minimum copper area of 15 mm² on the PCB top layer under the tab, with thermal vias to inner ground planes, to keep the junction temperature below 125 °C at 1 A output. The 0 °C to 125 °C operating range covers commercial and most industrial ambient temperatures, but not full automotive (-40 °C) environments.