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TC2054 データシート(PDF) 5 Page - Microchip Technology |
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TC2054 データシート(HTML) 5 Page - Microchip Technology |
5 / 16 page ![]() © 2002 Microchip Technology Inc. DS21663B-page 5 TC2054/2055/2186 4.0 THERMAL CONSIDERATIONS 4.1 Power Dissipation The amount of power the regulator dissipates is prima- rily a function of input and output voltage, and output current. The following equation is used to calculate worst case power dissipation: EQUATION 4-1: The maximum allowable power dissipation (Equation 4-2) is a function of the maximum ambient temperature (TA MAX), the maximum allowable die temperature (125 °C) and the thermal resistance from junction-to-air ( θJA). The 5-Pin SOT-23A package has a θJA of approximately 220°C/Watt when mounted on a typical two layer FR4 dielectric copper clad PC board. EQUATION 4-2: Equation 4-1 can be used in conjunction with Equation 4-2 to ensure regulator thermal operation is within lim- its. For example: Maximum allowable power dissipation: = 318mW In this example, the TC2054 dissipates a maximum of only 20.7mW; far below the allowable limit of 318mW. In a similar manner, Equation 4-1 and Equation 4-2 can be used to calculate maximum current and/or input voltage limits. 4.2 Layout Considerations The primary path of heat conduction out of the package is via the package leads. Therefore, layouts having a ground plane, wide traces at the pads, and wide power supply bus lines combine to lower θJA and, therefore, increase the maximum allowable power dissipation limit. PD ≈ (VIN –VOUT MIN )ILOAD MAX Where: PD = Worst case actual power dissipation VIN MAX = Maximum voltage on VIN VOUT MIN = Minimum regulator output voltage ILOAD MAX = Maximum output (load) current Where all terms are previously defined P D MA X T J MAX T A MA X – θ JA ----------------------------------- = Given: VINMAX =3.0V ±5% VOUTMIN = 2.7V – 2.5% ILOADMAX = 40mA TAMAX = 55°C Find : 1. Actual power dissapation 2. Maximum allowable dissapation Actual power dissipation: PD ≈ (VIN MAX –VOUT MIN )ILOADMAX = [(3.0 x 1.05) – (2.7 x .975)]40 x 10–3 = 20.7mW P D MA X T J MAX T A MA X – () θ JA -------------------------------------- = 125 55 – () 220 --------------------------- |
同様の部品番号 - TC2054 |
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同様の説明 - TC2054 |
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