Special attention has been given to noise, PSRR, and Rds(on) in the family of new LDOs. Rds(on) is the drain to source resistance of the pass element. The lower the resistance, the lower the input voltage to the LDO and higher the efficiency. The ADP120 and ADP121 are approx 600 mOhm devices, while the ADP130 and ADP170 are 200 mOhms.