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LM2937ES-8.0 bảng dữ liệu(PDF) 11 Page - Texas Instruments |
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LM2937ES-8.0 bảng dữ liệu(HTML) 11 Page - Texas Instruments |
11 / 24 page LM2937 www.ti.com SNVS100E – MARCH 2000 – REVISED APRIL 2013 HEATSINKING TO-220 PACKAGE PARTS The TO-220 can be attached to a typical heatsink, or secured to a copper plane on a PC board. If a copper plane is to be used, the values of θ(J−A) will be the same as shown in the next section for the DDPAK/TO-263. If a manufactured heatsink is to be selected, the value of heatsink-to-ambient thermal resistance, θ(H−A), must first be calculated: θ(H−A) = θ(J−A) − θ(C−H) − θ(J−C) where • θ(J−C) is defined as the thermal resistance from the junction to the surface of the case. A value of 3°C/W can be assumed for θ(J−C) for this calculation • θ(C−H) is defined as the thermal resistance between the case and the surface of the heatsink. The value of θ(C−H) will vary from about 1.5°C/W to about 2.5°C/W (depending on method of attachment, insulator, etc.). If the exact value is unknown, 2°C/W should be assumed for θ(C−H) (3) 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. θ(H−A) is specified numerically by the heatsink manufacturer in the catalog, or shown in a curve that plots temperature rise vs power dissipation for the heatsink. HEATSINKING DDPAK/TO-263 AND SOT-223 PACKAGE PARTS Both the DDPAK/TO-263 (“S”) and SOT-223 (“MP”) packages 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. Figure 26 shows for the DDPAK/TO-263 the measured values of θ(J−A) for different copper area sizes using a typical PCB with 1 ounce copper and no solder mask over the copper area used for heatsinking. Figure 26. θ(J−A) vs. Copper (1 ounce) Area for the DDPAK/TO-263 Package As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. It should also be observed that the minimum value of θ(J−A) for the DDPAK/TO-263 package mounted to a PCB is 32°C/W. As a design aid, Figure 27 shows the maximum allowable power dissipation compared to ambient temperature for the DDPAK/TO-263 device (assuming θ(J−A) is 35°C/W and the maximum junction temperature is 125°C). Copyright © 2000–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM2937 |
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