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Detail Description
The RS7202 is a low quiescent current LDO linear regulator. The device provides preset 1.8V, 2.5V and 3.3V output voltages
for output current up to 350mA. Other mask options for special output voltages from1.5V to 5.0V with 100mV increment are
also available. As illustrated in function block diagram, it consists of a 1.23V voltage, error amplifier, a P‐channel pass
transistor, an ON/OFF control logic, and an internal feedback voltage divider.
The 1.23V 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 VOUT pin. Additional blocks include with
output current limiter and shutdown logic.
Internal P‐channel Pass Transistor
The RS7202 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 RS7202 does
not suffer from these problems and consumes only 2.0μA (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 VIN and VOUT is switched off, allowing current
consumption to be drastically reduced. The VOUT pin enters the GND level due to the several MΩ resistance of the feedback
voltage divider between VOUT and GND pins.
Output Voltage Selection
The RS7202 output voltage is preset at an internally trimmed voltage 1.8V, 2.5V or 3.3V. The output voltage also can be
mask‐optioned from 1.2V to 5.0V with 100mV increment by special order (but only 1.28V in stead of 1.3V). The first two
digits of part number suffix identify the output voltage (see Ordering Information). For example, RS7202‐33 has a preset 3.3V
output voltage.
Current Limit
The RS7202 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 RS7202. When the junction temperature exceeds TJ=+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 RS7202 in the event of fault conditions. For continuous operation, the
maximum operating junction temperature rating of TJ=+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 RS7202 uses a P‐channel MOSFET
pass transistor, its dropout voltage is a function of drain‐to‐source on‐resistance (RDS(ON)) multiplied by the load current.
V
DROPOUT =VIN −VOUT = RDS (ON ) × IOUT
DS‐RS7202‐05
April, 2011
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ORISTER [ ORISTER CORPORATION ]
