SLVS582K April 2006 – December 2024 LP2950 , LP2951
PRODUCTION DATA
Dropout voltage (VDO) is defined as VIN – VOUT at the rated output current (IRATED), where the pass transistor is fully on. VIN is the input voltage, VOUT is the output voltage and IRATED is the maximum IOUT listed in the Section 5.3 table. At this operating point, the pass transistor is driven fully on. Dropout voltage indirectly specifies a minimum input voltage greater than the nominal programmed output voltage where the output voltage is expected to stay in regulation. If the input voltage falls to less than the nominal output regulation, then the output voltage falls as well.
For a CMOS regulator, the dropout voltage is determined by the drain-source on-state resistance (RDS(ON)) of the pass transistor. Therefore, if the linear regulator operates at less than the rated current, the dropout voltage for that current scales accordingly. The following equation calculates the RDS(ON) of the device.