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Detail Description
The RS7200 is a low quiescent current LDO linear regulator. The device provides preset 2.0V, 2.5V and 3.3V output voltages
for output current up to 500mA. Other mask options for special output voltages from 2.0V to 6.0V with 100mV increment are
also available. As illustrated in function block diagram, it consists of a 2.0V voltage, error amplifier, a P‐channel pass
transistor, an ON/OFF control logic, and an internal feedback voltage divider.
The 2.0V bandgap reference is connected to the error amplifier, which compares this reference with the feedback voltage
and amplifies the voltage difference. If the feedback voltage is lower than the reference voltage, the pass‐transistor gate is
pulled
lower, which allows more current to pass to the output pin and increases the output voltage. If the feedback voltage is too
high, the pass‐transistor gate is pulled up to decrease the output voltage.
The output voltage is feedback through an internal resistive divider connected to V
OUT
pin. Additional blocks include with
output current limiter and shutdown logic.
Internal P‐channel Pass Transistor
The RS7200 features a P‐channel MOSFET pass transistor. Unlike similar designs using PNP pass transistors, P‐channel
MOSFETs require no base drive, which reduces quiescent current. PNP–based regulators also waste considerable current in
dropout conditions when the pass transistor saturates, and use high base‐drive currents under large loads. The RS7200 does
not suffer from these problems and consumes only19μA (Typical) of current consumption under light loads.
Enable Function
EN pin starts and stops the regulator. When the EN pin is switched to the power off level, the operation of all internal circuit
stops, the build‐in P‐channel MOSFET output transistor between pins V
IN
and V
OUT
is switched off, allowing current
consumption to be drastically reduced. The V
OUT
pin enters the GND level due to the several MΩ resistance of the feedback
voltage divider between V
OUT
and GND pins.
Output Voltage Selection
The RS7200 output voltage is preset at an internally trimmed voltage 2.5V or 3.3V. The output voltage also can be mask‐
optioned from 2.0V to 5.0V with 100mV increment by special order. The first two digits of part number suffix identify the
output voltage (see Ordering Information). For example, RS7200‐33 has a preset 3.3V output voltage.
Current Limit
The RS7200 also includes a fold back current limiter. It monitors and controls the pass‐transistor’s gate voltage, estimates the
output current, and limits the output current within 350mA.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the RS7200. When the junction temperature exceeds T
J
=+155°C,
a thermal sensor turns off the pass transistor, allowing the IC to cool down. The thermal sensor turns the pass transistor
active again after the junction temperature cools down by 10°C, resulting in a pulsed output during continuous thermal
overload conditions.
Thermal overload protection is designed to protect the RS7200 in the event of fault conditions. For continuous operation, the
maximum operating junction temperature rating of T
J
=+125°C should not be exceeded.
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. The RS7200 uses a P‐channel MOSFET
pass transistor, its dropout voltage is a function of drain‐to‐source on‐resistance (R
DS(ON)
) multiplied by the load current.
V
DROPOUT
=
V
IN
−
V
OUT
=
R
DS
(
ON
)
×
I
OUT
DS‐RS7200‐02
September, 2009
www.Orister.com
ORISTER [ ORISTER CORPORATION ]
