Datasheet Si7850DP (Vishay) - 10

Application Note AN821
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PowerPAK® SO-8 Mounting and Thermal Considerations SYSTEM AND ELECTRICAL IMPACT OF
Suppose each device is dissipating 2.7 W. Using the
PowerPAK SO-8
junction-to-foot thermal resistance characteristics of the PowerPAK SO-8 and the standard SO-8, the die In any design, one must take into account the change in temperature is determined to be 107 °C for the PowerPAK MOSFET RDS(on) with temperature (figure 7). (and for DPAK) and 148 °C for the standard SO-8. This is a 2 °C rise above the board temperature for the PowerPAK On-Resistance vs. Junction Temperature and a 43 °C rise for the standard SO-8. Referring to figure 7, 1.8 a 2 °C difference has minimal effect on R ) DS(on) whereas a d e 43 °C difference has a significant effect on R z DS(on). il V GS = 10 V a 1.6 I D = 23 A m Minimizing the thermal rise above the board temperature by r o N using PowerPAK has not only eased the thermal design but ( ) 1.4 it has allowed the device to run cooler, keep rDS(on) low, and ( e permits the device to handle more current than the same c n a 1.2 t MOSFET die in the standard SO-8 package. siseR-
CONCLUSIONS
n 1.0 O - PowerPAK SO-8 has been shown to have the same thermal ) n 0.8 performance as the DPAK package while having the same o( S D footprint as the standard SO-8 package. The PowerPAK R SO-8 can hold larger die approximately equal in size to the 0.6 - 50 - 25 0 25 50 75 100 125 150 maximum that the DPAK can accommodate implying no sacrifice in performance because of package limitations. T J - Junction Temperature (°C) Recommended PowerPAK SO-8 land patterns are provided Fig. 7 MOSFET RDS(on) vs. Temperature to aid in PC board layout for designs using this new A MOSFET generates internal heat due to the current package. passing through the channel. This self-heating raises the Thermal considerations have indicated that significant junction temperature of the device above that of the PC advantages can be gained by using PowerPAK SO-8 board to which it is mounted, causing increased power devices in designs where the PC board was laid out for dissipation in the device. A major source of this problem lies the standard SO-8. Applications experimental data gave in the large values of the junction-to-foot thermal resistance thermal performance data showing minimum and of the SO-8 package. typical thermal performance in a SO-8 environment, plus PowerPAK SO-8 minimizes the junction-to-board thermal information on the optimum thermal performance resistance to where the MOSFET die temperature is very obtainable including spreading copper. This further close to the temperature of the PC board. Consider two emphasized the DPAK equivalency. devices mounted on a PC board heated to 105 °C by other PowerPAK SO-8 therefore has the desired small size components on the board (figure 8). characteristics of the SO-8 combined with the attractive thermal characteristics of the DPAK package. PowerPAK SO-8 Standard SO-8 107 °C 148 °C 0.8 °C/W 16 C/W N NOTE PC Board at 105 °C O Fig. 8 Temperature of Devices on a PC Board Revision: 16-Mai-13
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