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RT9167-16GS Datasheet(PDF) 10 Page - Richtek Technology Corporation |
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RT9167-16GS Datasheet(HTML) 10 Page - Richtek Technology Corporation |
10 / 13 page RT9167/A 10 DS9167/A-26 March 2007 www.richtek.com Operating Region and Power Dissipation The maximum power dissipation of RT9167/A 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 RT9167/A die junction and the surrounding environment, θJA is the thermal resistance from the junction to the surrounding environment. The GND pin of the RT9167/A 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 T9167 includes a current limit which monitors and controls the pass transistor's gate voltage limiting the output current to 350mA Typ. (700mA Typ. for RT9167A). Thermal- overload protection limits total power dissipation in the RT9167/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 RT9167/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 indefinite amount of time without damaging the part by cooperation of current limit and thermal protection. Thermal Considerations Thermal protection limits power dissipation in RT9167/A. When the operation junction temperature exceeds 165 °C, the OTP circuit starts the thermal shutdown function and turns the pass element off. The pass element turn on again after the junction temperature cools by 30 °C. For continuous operation, do not exceed absolute maximum operation junction temperature 125 °C. The power dissipation definition in device is: PD = (VIN − VOUT) x IOUT + VIN x IQ The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = ( TJ(MAX) - TA ) / θJA Where TJ(MAX) is the maximum operation junction temperature 125 °C, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9167/A, where TJ(MAX) is the maximum junction temperature of the die (125 °C) and TA is the operated ambient temperature. The junction to ambient thermal resistance θJA is layout dependent. For SOT-23-5 package, the thermal resistance θJA is 250°C/W on the standard JEDEC 51-3 single-layer thermal test board. The maximum power dissipation at TA = 25 °C can be calculated by following formula : PD(MAX) = (125 °C − 25°C) / 250 = 0.4W for SOT-23-5 package PD(MAX) = (125 °C - 25°C) / 160 = 0.625W for SOP-8 package The maximum power dissipation depends on operating ambient temperature for fixed TJ(MAX) and thermal resistance θJA. For RT9167/A packages, the Figure 5 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Figure 5. Derating Curves for RT9167/A Packages 0 100 200 300 400 500 600 700 0 20 40 60 80 100 120 140 Ambient Temperature SOT-23-5 SOP-8 |
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