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Detail Description
The RS7215 is a low‐dropout linear regulator. The device provides preset 1.8V, 2.5V and 3.3V output voltages for output
current up to 1.0A. Adjustable output voltage and other mask options for special output voltages are also available. As
illustrated in function block diagram, it consists of a 1.175V bandgap (Fixed voltage type is 0.95V) reference, an error
amplifier, a P‐channel pass transistor and an internal feedback voltage divider.
The bandgap reference for fixed voltage types 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 feed back through an internal resistive divider (or external resistive divider for adjustable output
voltage type) connected to VOUT pin. Additional blocks include an output current limiter, thermal sensor, and shutdown logic.
Internal P‐channel Pass Transistor
The RS7215 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 when the pass transistor saturates, and use high base‐drive currents under large loads. The RS7215 does not suffer
from these problems and consumes only 60μA (Typ.) of current consumption under heavy loads as well as in dropout
conditions.
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 through the internal discharge path between VOUT
and GND pins.
Fast Discharge Function
The RS7215 fixed type has fast discharge Function on EN pin disable. When user turns off the device, its internal pull‐low
resistor will discharge output capacitor charge. It’ll avoid other device to arise wrong motions.
Output Voltage Selection
For fixed voltage type of RS7215, the output voltage is preset at an internally trimmed voltage. The first two digits of part
number suffix identify the output voltage (see Ordering Information). For example, the RS7215‐33 has a preset 3.3V output
voltage.
For adjustable voltage type of RS7215, the output voltage is set by comparing the feedback voltage at adjust terminal to the
internal bandgap reference voltage. The reference voltage VREF is 1.175V. The output voltage is given by the equation:
R1
R2
⎛
⎞
⎟
VOUT =VREF × 1 +
⎜
⎝
⎠
Current Limit
The RS7215 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 1.3A.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the RS7215. When the junction temperature exceeds TJ=+150°C,
a thermal sensor turns off the pass transistor, allowing the IC to cool down. The thermal sensor turns the pass transistor on
again after the junction temperature cools down by 20°C, resulting in a pulsed output during continuous thermal overload
conditions.
Thermal overload protection is designed to protect the RS7215 in the event of fault conditions. For continuous operation, the
absolute maximum operating junction temperature rating of TJ=+125°C should not be exceeded.
DS‐RS7215‐02 September, 2009
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