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RT9182CGES Datasheet(PDF) 7 Page - Richtek Technology Corporation |
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RT9182CGES Datasheet(HTML) 7 Page - Richtek Technology Corporation |
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7 / 9 page  RT9182 7 DS9182-17 March 2007 www.richtek.com Applications Information 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. Shutdown The RT9182 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 floating). Internal P-Channel Pass Transistor The RT9182 features double typical 1.5 Ω 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 165 μA 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. 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 event of fault conditions. Do not exceed the absolute maximum junction tempera- ture rating of TJ = + 125 °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. 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 : P(MAX) = (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. Capacitor Selection and Regulator Stability Like any low-dropout regulator, the external capacitors used with the RT9182 must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1 μF on the RT9182 input and the amount of capacitance can be increased without limit. The input capacitor must be located a distance of not more than 0.5" from the input pin of the IC and returned to a clean analog ground. Any good quality ceramic or tantalum can be used for this capacitor. The capacitor with larger value and lower ESR (equivalent series resistance) provides better PSRR and line- transient response. The output capacitor must meet both requirements for minimum amount of capacitance and ESR in all LDO applications (see Figure1). The RT9182 is designed specifically to work with low ESR ceramic output capacitor in space-saving and performance consideration. Using a ceramic capacitor whose value is at least 1 μF with ESR is > 5m Ω on the RT9182 output ensures stability. The RT9182 still works well with output capacitor of other types due to the wide stable ESR range. Output capacitor |
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