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TC1054 Fiches technique(PDF) 10 Page - Microchip Technology |
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TC1054 Fiches technique(HTML) 10 Page - Microchip Technology |
10 / 20 page TC1054/TC1055/TC1186 DS21350E-page 10 2002-2012 Microchip Technology Inc. 5.0 THERMAL CONSIDERATIONS 5.1 Thermal Shutdown Integrated thermal protection circuitry shuts the regulator off when die temperature exceeds +160°C. The regulator remains off until the die temperature drops to approximately +150°C. 5.2 Power Dissipation The amount of power the regulator dissipates is primarily a function of input voltage, output voltage and output current. The following equation is used to calculate worst-case actual power dissipation: EQUATION 5-1: The maximum allowable power dissipation (Equation 5-2) is a function of the maximum ambient temperature (TAMAX), the maximum allowable die temperature (TJMAX) and the thermal resistance from junction-to-air ( JA). The 5-Pin SOT-23 package has a JA of approximately 220°C/Watt. EQUATION 5-2: Equation 5-1 can be used in conjunction with Equation 5-2 to ensure regulator thermal operation is within limits. For example: Actual power dissipation: Maximum allowable power dissipation: In this example, the TC1054 dissipates a maximum of 20.7 mW; below the allowable limit of 318 mW. In a similar manner, Equation 5-1 and Equation 5-2 can be used to calculate maximum current and/or input voltage limits. 5.3 Layout Considerations The primary path of heat conduction out of the package is via the package leads. Layouts having a ground plane, wide traces at the pads and wide power supply bus lines, combine to lower θJA and increase the max- imum allowable power dissipation limit. P D V INMAX V OUTMIN – I LOADMAX Where: PD = Worst-case actual power dissipation VINmax = Maximum voltage on VIN VOUTmin = Minimum regulator output voltage ILOADmax = Maximum output (load) current Where all terms are previously defined. P DMAX T JMAX T AMAX – JA -------------------------------------------- = Given: VINMAX = 3.0V +5% VOUTMIN = 2.7V – 2.5% ILOADMAX = 40 mA TJMAX = +125°C TAMAX = +55°C Find: 1. Actual power dissipation 2. Maximum allowable dissipation P D V INMAX V OUTMIN – I LOADMAX 3.0 1.05 2.7 0.975 – 40 10-3 = 20.7mW = P DMAX T JMAX T AMAX – JA -------------------------------------------- = 125 55 – 220 ------------------------- = 318mW = |
Numéro de pièce similaire - TC1054_12 |
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Description similaire - TC1054_12 |
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