RT9181CB datasheet(6/10 Pages) RICHTEK

6 / 10 page

RT9181

Preliminary

www.richtek-ic.com.tw

DS9181-00 February 2002

Timing Diagram

Application Guides

CE/Shutdown

The RT9181 is enabled by driving the CE input high,

and shutdown by pulling the input low. If this feature

is not to be used, the CE input should be tied to VIN

to keep the regulator enabled at all times (the CE

input must not be left floating).

Internal P-Channel Pass Transistor

The RT9181 features a 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 RT9181 does not

suffer from these problems and consume only 160

µA

of quiescent current whether in dropout, light-load, or

heavy-load applications.

Power Good

The power good output is an open-drain output. It is

designed essentially to work as a power-on reset

generator once the regulated voltage was up or a

fault condition. The output of the power good drives

low when a fault condition occurs. The power good

output come back up once the output has reached

90% of its nominal value and a 2.0ms (typ.) delay

has passed. See Timing Diagram. The output voltage

level will be drooped at the fault conditions including

current limit, thermal shutdown, or shutdown and

triggers the POG detector to alarm a fault condition.

This output is fed into an on-board delay circuitry that

drives the open drain transistor to indicate a fault.

Because at shutdown mode, a fault condition occurs

by pulling the POG output low, it will sink a current

from the open drain and the external power.

Selecting a suitable pulling resistance will be well to

control this dissipated power.

Current Limit and Thermal Protection

The RT9181 includes a current limit structure which

monitor and control the pass transistor’s gate voltage

limiting the guaranteed maximum output current to

150mA minimum.

Thermal-overload

protection

limits

total

power

dissipation in the RT9181. When the junction

temperature exceeds TJ = +150

°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 20

°C,

resulting in a pulsed output during continuous

thermal-overload

conditions.

Thermal-overloaded

protection is designed to protect the RT9181 in the

event of fault conditions. Do not exceed the absolute

maximum junction-temperature rating of TJ = +125

°C

for continuous operation. The output can be shorted

to ground for and indefinite amount of time without

damaging the part by cooperation of current limit and

thermal protection.

Operating Region and Power Dissipation

The maximum power dissipation of RT9181 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 air flow. The

90% max of VOUT (normal)

td(POG) 2.0ms typ.

VOUT

POG

VPOGL

85% min

VPOGH

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