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# N07A View Datasheet(PDF) - National ->Texas Instruments

 Part Name Description Manufacturer N07A 3-Terminal Adjustable Regulator National ->Texas Instruments N07A Datasheet PDF : 26 Pages
 1 2 3 4 5 6 7 8 9 10 Next Last diodes included for use with outputs greater than 25V and high values of output capacitance. 906307 (2) D1 protects against C1 D2 protects against C2 FIGURE 3. Regulator with Protection Diodes HEATSINK REQUIREMENTS The LM317 regulators have internal thermal shutdown to pro- tect the device from over-heating. Under all operating condi- tions, the junction temperature of the LM317 should not exceed the rated maximum junction temperature (TJ) of 150° C for the LM117, or 125°C for the LM317A and LM317. A heatsink may be required depending on the maximum device power dissipation and the maximum ambient temperature of the application. To determine if a heatsink is needed, the power dissipated by the regulator, PD, must be calculated: PD = ((VIN − VOUT) × IL) + (VIN × IG) (3) Figure 4 shows the voltage and currents which are present in the circuit. The next parameter which must be calculated is the maximum allowable temperature rise, TR(MAX): TR(MAX) = TJ(MAX) − TA(MAX) (4) where TJ(MAX) is the maximum allowable junction temperature (150°C for the LM117, or 125°C for the LM317A/LM317), and TA(MAX) is the maximum ambient temperature which will be encountered in the application. Using the calculated values for TR(MAX) and PD, the maximum allowable value for the junction-to-ambient thermal resistance (θJA) can be calculated: θJA = (TR(MAX) / PD) (5) 906360 FIGURE 4. Power Dissipation Diagram If the calculated maximum allowable thermal resistance is higher than the actual package rating, then no additional work is needed. If the calculated maximum allowable thermal re- sistance is lower than the actual package rating either the power dissipation (PD) needs to be reduced, the maximum ambient temperature TA(MAX) needs to be reduced, the ther- mal resistance (θJA) must be lowered by adding a heatsink, or some combination of these. If a heatsink is needed, the value can be calculated from the formula: θHA ≤ (θJA - (θCH + θJC)) (6) where (θCH is the thermal resistance of the contact area be- tween the device case and the heatsink surface, and θJC is thermal resistance from the junction of the die to surface of the package case. When a value for θ(H−A) is found using the equation shown, a heatsink must be selected that has a value that is less than, or equal to, this number. The θ(H−A) rating is specified numerically by the heatsink man- ufacturer in the catalog, or shown in a curve that plots tem- perature rise vs power dissipation for the heatsink. HEATSINKING SURFACE MOUNT PACKAGES The TO-263 (S), SOT-223 (EMP) and TO-252 (MDT) pack- ages use a copper plane on the PCB and the PCB itself as a heatsink. To optimize the heat sinking ability of the plane and PCB, solder the tab of the package to the plane. HEATSINKING THE SOT-223 PACKAGE Figure 5 and Figure 6 show the information for the SOT-223 package. Figure 6 assumes a θ(J−A) of 74°C/W for 1 ounce copper and 51°C/W for 2 ounce copper and a maximum junc- tion temperature of 125°C. Please see AN-1028 for thermal enhancement techniques to be used with SOT-223 and TO-252 packages. 9 www.national.com