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LM1117QS-3.3 Datasheet(PDF) 11 Page - HTC Korea TAEJIN Technology Co. |
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LM1117QS-3.3 Datasheet(HTML) 11 Page - HTC Korea TAEJIN Technology Co. |
11 / 11 page 1A L.D.O VOLTAGE REGULATOR(Automotive Grade) LM1117Q Jul. 2011 Rev. 1.0 - 11 - HTC APPLICATION INFORMATION Maximum Output Current Capability The LM1117Q can deliver a continuous current of 1A over the full operating junction temperature range. However, the output current is limited by the restriction of power dissipation which differs from packages. A heat sink may be required depending on the maximum power dissipation and maximum ambient temperature of application. With respect to the applied package, the maximum output current of 1A may be still undeliverable due to the restriction of the power dissipation of LM1117Q. Under all possible conditions, the junction temperature must be within the range specified under operating conditions. The temperatures over the device are given by: TC = TA + PD X θCA / TJ = TC + PD X θJC / TJ = TA + PD X θJA where TJ is the junction temperature, TC is the case temperature, TA is the ambient temperature, PD is the total power dissipation of the device, θCA is the thermal resistance of case-to-ambient, θJC is the thermal resistance of junction-to-case, and θJA is the thermal resistance of junction to ambient. The total power dissipation of the device is given by: PD = PIN – POUT = (VIN X IIN)–(VOUT X IOUT) = (VIN X (IOUT+IGND)) – (VOUT X IOUT) = (VIN - VOUT) X IOUT + VIN X IGND where IGND is the operating ground current of the device which is specified at the Electrical Characteristics. The maximum allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax) of the application, and the maximum allowable junction temperature (TJmax): TRmax = TJmax – TAmax The maximum allowable value for junction-to-ambient thermal resistance, θJA, can be calculated using the formula: θJA = TRmax / PD = (TJmax – TAmax) / PD LM1117Q is available in SOT223 package. The thermal resistance depends on amount of copper area or heat sink, and on air flow. If the maximum allowable value of θJA calculated above is over 137°C/W for SOT-223 package, no heat sink is needed since the package can dissipate enough heat to satisfy these requirements. If the value for allowable θJA falls near or below these limits, a heat sink or proper area of copper plane is required. In summary, the absolute maximum ratings of thermal resistances are as follow: Absolute Maximum Ratings of Thermal Resistance Characteristic Symbol Rating Unit Thermal Resistance Junction-To-Ambient / SOT-223 θJA-SOT-223 137 °C/W No heat sink / No air flow / No adjacent heat source / 0.066 inch 2 copper area. (T A=25°C) |
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