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[v2-00] 2016-Jun-01

AS1370 − Application Information

Dropout Voltage

Dropout is the input to output voltage difference, below which

the linear regulator ceases to regulate. At this point, the output

voltage change follows the input voltage change. Dropout

voltage may be measured at different currents and in particular

at the regulator maximum one. From this the MOSFET maximum

series resistance over temperature is obtained. More generally:

Dropout is a key specification when the regulator is used in a

battery application. The dropout performance of the regulator

defines the useful “end of life” of the battery before

replacement or re-charge is required.

Figure 16:

Graphical Representation of Dropout Voltage

Figure 16 shows the variation of VOUT as VIN is varied for a

certain load current. The practical value of dropout is the

differential voltage (VOUT - VIN) measured at the point where

the LDO output voltage has fallen by 100mV below the nominal,

fully regulated output value. The nominal regulated output

voltage of the LDO is that obtained when there is 500mV (or

greater) input-output voltage differential.

Application Information

(EQ1)

DROPOUT

LOAD

SERIES

VOUT

VIN

VOUT

VIN ≥ VOUT + 0.5V

100mV

Dropout

Voltage

AS1370 Datasheet(PDF) 14 Page - ams AG