RT9182ACE datasheet(8/10 Pages) RICHTEK

8 / 10 page

RT9182

Preliminary

www.richtek-ic.com.tw

DS9182-02 April 2002

Input-Output (Dropout) Voltage

regulator’s

minimum

input-output

voltage

differential (or dropout voltage) determines the lowest

usable supply voltage. In battery-powered systems,

this will determine the useful end-of-life battery

voltage. Because the RT9182 uses a P-channel

MOSFET pass transistor, the dropout voltage is a

function of drain-to-source on-resistance [RDS(ON)]

multiplied by the load current.

Reverse Current Path

The power transistor used in the RT9182 has an

inherent diode connected between each regulator

input and output (see Fig.2). If the output is forced

above the input by more than a diode-drop, this diode

will become forward biased and current will flow from

the VOUT terminal to VIN. This diode will also be

turned on by abruptly stepping the input voltage to a

value below the output voltage. To prevent regulator

mis-operation, a Schottky diode could be used in the

applications where input/output voltage conditions

can cause the internal diode to be turned on (see

Fig.3). As shown, the Schottky diode is connected in

parallel with the internal parasitic diode and prevents

it from being turned on by limiting the voltage drop

across it to about 0.3V < 100mA to prevent damage

to the part.

Fig. 2

Fig. 3

VIN

VOUT

VIN

VOUT

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