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## TC1269 Datasheet(PDF) 5 Page - Microchip Technology

 Part No. TC1269 Description 300mA CMOS LDO with Shutdown and VREF Bypass Download 12 Pages Scroll/Zoom 100% Maker MICROCHIP [Microchip Technology] Homepage http://www.microchip.com Logo

## TC1269 Datasheet(HTML) 5 Page - Microchip Technology

 5 / 12 page © 2002 Microchip Technology Inc.DS21380B-page 5TC12694.0THERMAL CONSIDERATIONS4.1Thermal ShutdownIntegratedthermalprotectioncircuitryshutstheregulator off when die temperature exceeds 150°C.The regulator remains off until the die temperaturedrops to approximately 140°C.4.2Power DissipationThe amount of power the regulator dissipates isprimarily a function of input and output voltage, andoutput current. The following equation is used tocalculate worst case actual power dissipation:EQUATION 4-1:Themaximumallowablepowerdissipation(Equation 4-2) is a function of the maximum ambienttemperature (TAMAX), the maximum allowable dietemperature (TJMAX) and the thermal resistance fromjunction-to-air (θJA).EQUATION 4-2:Equation 4-1canbeusedinconjunctionwithEquation 4-2 to ensure regulator thermal operation iswithin limits. For example:Given:VINMAX= 3.0V ± 10%VOUTMIN =2.7V – 2.5%ILOAD= 250mATAMAX=55°CFind: 1. Actual power dissipation2. Maximum allowable dissipationActual power dissipation:PD ≈ (VINMAX –VOUTMIN)ILOADMAX= [(3.0 x 1.1) – (2.7 x .975)]250 x 10-3= 167mWMaximum allowable power dissipation:In this example, the TC1269 dissipates a maximum of167mW; below the allowable limit of 350mW. In asimilar manner, Equation 4-1 and Equation 4-2 can beused to calculate maximum current and/or inputvoltage limits.4.3Layout ConsiderationsThe primary path of heat conduction out of the packageis via the package leads. Therefore, layouts having aground plane, wide traces at the pads, and wide powersupply bus lines combine to lowerθJA and, therefore,increase the maximum allowable power dissipationlimit.Where:PD ≈ (VINMAX –VOUTMIN)ILOADMAXPDVINMAXVOUTMINILOADMAX= Worst case actual power dissipation= Minimum regulator output voltage= Maximum output (load) current= Maximum voltage on VINPDMAX =(TJMAX – TAMAX)θJAWhere all terms are previously defined.PDMAX =(TJMAX –TAMAX)θJA= (125 – 55)200= 350mW

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