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DS-RS7225-02

September, 2009

www.Orister.com

Detail Description

The RS7225 is a low-dropout linear regulator. The device provides preset 1.8V, 2.5V and 3.3V output voltages for output

current up to 600mA. Other mask options for special output voltages are also available. As illustrated in function block diagram,

it consists of a 0.95V bandgap reference, an error amplifier, a P-channel pass transistor and an internal feedback voltage

divider.

The 0.95V 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.

current limiter, thermal sensor, and shutdown logic.

Internal P-channel Pass Transistor

The RS7225 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 RS7225 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

Soft Start Function

The capacitor can be connected between the BYPASS pin and GND. This capacitor can be a low cost Polyester Film variety. A

larger capacitor improves the AC ripple rejection, but also makes the output come up slowly. This "Soft" turn-on is desirable in

some applications to limit turn-on surges.

Fast Discharge Function

The RS7225 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 RS7225, 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 RS7225-33 has a preset 3.3V output

voltage.

Current Limit

The RS7225 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 (Typ.)

Thermal Overload Protection

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 RS7225 in the event of fault conditions. For continuous operation, the