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RT9182

Dual, Low-Noise, 200mA LDO Regulator

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RT9182

Preliminary

Functional Description

The RT9182 is integrated with two low noise, low

dropout, and low quiescent current linear regulators

designed primarily for battery-powered applications.

Output voltages are optional ranging from 1.5V to

3.3V, and each channel can supply current up to

200mA.

event of fault conditions. Do not exceed the absolute

maximum junction-temperature rating of TJ = +150°C

for continuous operation. The output can be shorted

to ground for an indefinite amount of time without

damaging the part by cooperation of current limit and

thermal protection.

Shutdown

The RT9182 is shutdown by pulling the SHDN input

low, and turned on by driving the input high. If this

feature is not to be used, the SHDN input should be

tied to VIN to keep the regulator on at all times (the

SHDN input must not be left floating).

Internal P-Channel Pass Transistor

The RT9182 features double typical 1.5Ω P-channel

MOSFET pass transistors. It provides several

advantages over similar designs using PNP pass

transistors, including longer battery life. The P-

channel MOSFET requires no base drive, which

reduces quiescent current considerably. PNP-based

regulators waste considerable current in dropout

when the pass transistor saturates. They also use

high base-drive currents under large loads. The

RT9182 does not suffer from these problems and

consume only 165µA of quiescent current whether in

dropout, light-load, or heavy-load applications.

Current Limit and Thermal Protection

The RT9182 includes two independent current limit

structure which monitor and control each pass

transistor’s gate voltage limiting the guaranteed

maximum output current to 200mA minimum.

Operating Region and Power Dissipation

The maximum power dissipation of RT9182 depends

on the thermal resistance of the case and circuit

board, the temperature difference between the die

junction and ambient air, and the rate of airflow. The

power dissipation across the device is

P = IOUT (VIN - VOUT).

The maximum power dissipation is:

PMAX = (TJ - TA) / θJA

where TJ - TA is the temperature difference between

the RT9182 die junction and the surrounding

environment, θJA is the thermal resistance from the

junction to the surrounding environment. The GND

pin of the RT9182 performs the dual function of

providing an electrical connection to ground and

channeling heat away. Connect the GND pin to

ground using a large pad or ground plane.

Low-Noise Operation

An external 10nF bypass capacitor at BP, in

conjunction with an internal resistor, creates a

lowpass filter. The RT9182 exhibits 29µVRMS of

output voltage noise with CBP = 10nF and COUT =

2.2µF.

Thermal-overload protection limits total power

dissipation in the RT9182. When the junction

temperature exceeds TJ = +140°C, the thermal

sensor signals the shutdown logic turning off the

pass transistor and allowing the IC to cool. The

thermal sensor will turn the pass transistor on again

after the IC’s junction temperature cools by 10°C,

resulting in a pulsed output during continuous

thermal-overload conditions. Thermal-overloaded

protection is designed to protect the RT9182 in the

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DS9182-02 April 2002

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