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RT9167-18GB Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9167-18GB Datasheet(HTML) 8 Page - Richtek Technology Corporation |
8 / 10 page RT9167B 8 DS9167B-01 April 2011 www.richtek.com Load-Transient Considerations The RT9167B load-transient response graphs (see Typical Operating Characteristics) show two components of the output response : a DC shift from the output impedance due to the load current change, and the transient response. The DC shift is quite small due to the excellent load regulation of the IC. Typical output voltage transient spike for a step change in the load current from 0mA to 50mA is tens mV, depending on the ESR of the output capacitor. Increasing the output capacitor's value and decreasing the ESR attenuates the overshoot. Shutdown Input Operation The RT9167B is shutdown by pulling the EN input low, and turned on by driving the input high. If this feature is not to be used, the EN input should be tied to VIN to keep the regulator on at all times (the EN input must not be left floating). To ensure proper operation, the signal source used to drive the EN 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 RT9167B input voltage or another logic supply. The high-level voltage may exceed the RT9167B input voltage, but must remain within the absolute maximum ratings for the EN pin. 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 RT9167B 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. Operating Region and Power Dissipation The maximum power dissipation of RT9167B 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 RT9167B die junction and the surrounding environment, θJA is the thermal resistance from the junction to the surrounding environment. The GND pin of the RT9167B 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. Current Limit and Thermal Protection The RT9167B includes a current limit which monitors and controls the pass transistor's gate voltage limiting the output current to 400mA min. Thermal-overload protection limits total power dissipation in the RT9167B. 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 RT9167B 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 indefinite amount of time without damaging the part by cooperation of current limit and thermal protection. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJAis the junction to ambient thermal resistance. For recommended operating condition specifications of the RT9167B, the maximum junction temperature is 125 °C and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For MSOP- |
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Similar Description - RT9167-18GB |
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