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RT9168A-49CBR Datasheet(PDF) 8 Page - List of Unclassifed Manufacturers |
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RT9168A-49CBR Datasheet(HTML) 8 Page - List of Unclassifed Manufacturers |
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8 / 13 page  RT9168/A www.richtek-ic.com.tw DS9168/A-03 May 2001 8 To ensure proper operation, the signal source used to drive the SHDN input must be able to swing above and below the specified turn-on/turn-off voltage thresholds which guarantee an ON or OFF state (see Electrical Characteristics). The ON/OFF signal may come from either CMOS output, or an open-collector output with pull-up resistor to the RT9168/A input voltage or another logic supply. The high-level voltage may exceed the RT9168/A input voltage, but must remain within the absolute maximum ratings for the SHDN pin. Internal P-Channel Pass Transistor The RT9168/A features a typical 1.1 Ω P-channel MOSFET pass transistor. 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 RT9168/A does not suffer from these problems and consume only 80µA of quiescent current whether in dropout, light-load, or heavy-load applications. Input-Output (Dropout) Voltage A regulator’s minimum input-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this will determine the useful end-of-life battery voltage. Because the RT9168/A uses a P- channel MOSFET pass transistor, the dropout voltage is a function of drain-to-source on-resistance [RDS(ON)] multiplied by the load current. Reverse Current Path The power transistor used in the RT9168/A has an inherent diode connected between the regulator input and output (see Fig.2). If the output is forced above the input by more than a diode-drop, this diode will become forward biased and current will flow from the VOUT terminal to VIN. This diode will also be turned on by abruptly stepping the input voltage to a value below the output voltage. To prevent regulator mis-operation, a Schottky diode should be used in any applications where input/output voltage conditions can cause the internal diode to be turned on (see Fig.3). As shown, the Schottky diode is connected in parallel with the internal parasitic diode and prevents it from being turned on by limiting the voltage drop across it to about 0.3V. < 100 mA to prevent damage to the part. Current Limit and Thermal Protection The RT9168 includes a current limit which monitors and controls the pass transistor’s gate voltage limiting the output current to 300mA Typ. (700mA Typ. for RT9168A). Thermal-overload protection limits total power dissipation in the RT9168/A. When the junction temperature exceeds TJ = +155°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 RT9168/A in the 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 Fig. 2 VIN VOUT Fig. 3 VIN VOUT |
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