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TPS79428DCQR Datasheet(PDF) 11 Page - Texas Instruments |
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TPS79428DCQR Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page www.ti.com T J + TA ) PD max RθJA (6) RθJA + T J * TA P D max (7) P D max + (3.3 * 2.5) V 1A + 800mW (8) RθJA max + (125 * 55)°C 800mW + 87.5°C W 0 100 120 140 160 180 No Air Flow 80 60 40 20 0.1 1 10 PCB Copper Area (in2) SOT223 POWER DISSIPATION 0 1 2 3 6 0 25 50 75 100 150 125 TA = 25°C TA − Ambient Temperature (°C) 4 5 4 in2 PCB Area 0.5 in2 PCB Area TPS794xx SLVS349E – NOVEMBER 2001 – REVISED DECEMBER 2005 Equation 5 simplifies into Equation 6: applications. The SOT223 package dimensions are provided in the Mechanical Data section at the end of the data sheet. The addition of a copper plane Rearranging Equation 6 gives Equation 7: directly underneath the SOT223 package enhances the thermal performance of the package. To illustrate, the TPS79425 in a SOT223 package was chosen. For this example, the average input Using Equation 6 and the computer model generated voltage is 3.3 V, the output voltage is 2.5 V, the curves shown in Figure 25, a designer can quickly average output current is 1 A, the ambient compute the required heatsink thermal temperature 55 °C, no air flow is present, and the resistance/board area for a given ambient operating environment is the same as documented temperature, power dissipation, and operating below. Neglecting the quiescent current, the environment. maximum average power is Equation 8: Substituting TJmax for TJ into Equation 4 gives Equation 9: (9) From Figure 25, RθJA vs PCB Copper Area, the ground plane needs to be 0.55 in2 for the part to dissipate 800 mW. The operating environment used to construct Figure 25 consisted of a board with 1 oz. copper planes. The package is soldered to a 1 oz. copper pad on the top of the board. The pad is tied through thermal vias to the 1 oz. ground plane. From the data in Figure 25 and rearranging equation 6, the maximum power dissipation for a different ground plane area and a specific ambient temperature can be computed, as shown in Figure 26. Figure 25. SOT223 Thermal Resistance vs PCB Copper Area The SOT223 package provides an effective means of managing power dissipation in surface-mount Figure 26. SOT223 Maximum Power Dissipation vs Ambient Temperature 11 Submit Documentation Feedback |
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