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RT9181 Datasheet(PDF) 6 Page - Richtek Technology Corporation |
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RT9181 Datasheet(HTML) 6 Page - Richtek Technology Corporation |
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6 / 10 page  RT9181 Preliminary www.richtek-ic.com.tw DS9181-00 February 2002 6 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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