RT9182ACE RICHTEK [Richtek Technology Corporation], RT9182ACE Datasheet - Page 8

• Manufacturer Part Number: RT9182ACE
• Description: DUAL, LOW-NOISE, 200mA LDO REGULATOR
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9182
Preliminary
Input-Output (Dropout) Voltage
A
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 [R
]
DS(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 V
terminal to V
. This diode will also be
OUT
IN
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.
V
V
IN
OUT
Fig. 2
V
V
IN
OUT
Fig. 3
www.richtek-ic.com.tw
DS9182-02 April 2002
8