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TPS78633KTTRG3 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS78633KTTRG3 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 21 page www.ti.com T J + TA ) PDmax R qJA (6) R qJA + T J * TA P Dmax (7) 15 20 25 30 35 40 0.1 1 10 100 PCB Copper Area (cm2) No Air Flow 150 LFM 250 LFM DDPAK POWER DISSIPATION 1 oz. Copper Power Plane 1 oz. Copper Ground Plane 2 oz. Copper Solder Pad with 25 Thermal Vias Thermal Vias, 0.3 mm Diameter, 1.5 mm Pitch P Dmax + (5 * 2.5) V 1 A + 2.5 W (8) R qJA max + (125 * 55)°C 2.5 W + 28°C W (9) TPS786xx SLVS389G – SEPTEMBER 2002 – REVISED JULY 2006 Even if no external black body radiator type heatsink From Figure 27, DDPAK Thermal Resistance vs is attached to the package, the board on which the Copper Heatsink Area, the ground plane needs to be regulator is mounted provides some heatsinking 1 cm2 for the part to dissipate 2.5 W. The operating through the pin solder connections. Some packages, environment used in the computer model to construct like the DDPAK and SOT223 packages, use a Figure 27 consisted of a standard JEDEC High-K copper plane underneath the package or the circuit board (2S2P) with a 1 oz. internal copper plane and board ground plane for additional heatsinking to ground plane. The package is soldered to a 2 oz. improve their thermal performance. Computer-aided copper pad. The pad is tied through thermal vias to thermal modeling can be used to compute very the 1 oz. ground plane. Figure 28 shows the side accurate approximations of an integrated circuit's view of the operating environment used in the thermal performance in different operating computer model. environments (for example, different types of circuit boards, different types and sizes of heatsinks, different air flows, etc.). Using these models, the three thermal resistances can be combined into one thermal resistance between junction and ambient (RθJA). This RθJA is valid only for the specific operating environment used in the computer model. Equation 5 simplifies into Equation 6: Rearranging Equation 6 gives Equation 7: Using Equation 6 and the computer model generated curves shown in Figure 27 and Figure 30, a designer can quickly compute the required heatsink thermal resistance/board area for a given ambient temperature, power dissipation, and operating Figure 27. DDPAK Thermal Resistance environment. vs PCB Copper Area The DDPAK package provides an effective means of managing power dissipation in surface mount applications. The DDPAK package dimensions are provided in the mechanical drawing section at the end of the data sheet. The addition of a copper plane directly underneath the DDPAK package enhances the thermal performance of the package. To illustrate, the TPS78625 in a DDPAK package was chosen. For this example, the average input voltage is 5 V, the output voltage is 2.5 V, the average output current is 1 A, the ambient temperature 55 °C, the air flow is 150 LFM, and the operating environment is the same as documented below. Neglecting the quiescent current, the maximum average power is shown in Equation 8: Figure 28. DDPAK Thermal Resistance Computer Model Substituting TJmax for TJ into Equation 6 gives Equation 9: 11 Submit Documentation Feedback |
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