how to understand dropout voltage in LDO datasheet?

Hi Junge,

In the ADP1741 data sheet, dropout voltage is defined as " the input to output voltage differential when the input voltage is set to the nominal output voltage. This applies only to output voltages above 1.6 V." If your input voltage is greater than the nominal output voltage, then the part is not in dropout mode. To meet the specifications given on table 1 of the datasheet, a minimum headroom of 400mV must be kept between VIN to VOUT unless otherwise specified.

Thanks,
Alex

"Vin - Vout" should be greater than dropout voltage to make ADP1741 work normally.