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SI5457DC Datasheet(PDF) 8 Page - Vishay Siliconix |
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SI5457DC Datasheet(HTML) 8 Page - Vishay Siliconix |
8 / 11 page AN811 Vishay Siliconix Document Number: 71126 12-Dec-03 www.vishay.com 1 Single-Channel 1206-8 ChipFETr Power MOSFET Recommended Pad Pattern and Thermal Performance INTRODUCTION New Vishay Siliconix ChipFETs in the leadless 1206-8 package feature the same outline as popular 1206-8 resistors and capacitors but provide all the performance of true power semiconductor devices. The 1206-8 ChipFET has the same footprint as the body of the LITTLE FOOTR TSOP-6, and can be thought of as a leadless TSOP-6 for purposes of visualizing board area, but its thermal performance bears comparison with the much larger SO-8. This technical note discusses the single-channel ChipFET 1206-8 pin-out, package outline, pad patterns, evaluation board layout, and thermal performance. PIN-OUT Figure 1 shows the pin-out description and Pin 1 identification for the single-channel 1206-8 ChipFET device. The pin-out is similar to the TSOP-6 configuration, with two additional drain pins to enhance power dissipation and thermal performance. The legs of the device are very short, again helping to reduce the thermal path to the external heatsink/pcb and allowing a larger die to be fitted in the device if necessary. Single 1206-8 ChipFET D D D G D D D S 1 Bottom View FIGURE 1. For package dimensions see the 1206-8 ChipFET package outline drawing (http://www.vishay.com/doc?71151). BASIC PAD PATTERNS The basic pad layout with dimensions is shown in Application Note 826, Recommended Minimum Pad Patterns With Outline Drawing Access for Vishay Siliconix MOSFETs, (http://www.vishay.com/doc?72286). This is sufficient for low power dissipation MOSFET applications, but power semiconductor performance requires a greater copper pad area, particularly for the drain leads. FIGURE 2. Footprint With Copper Spreading 80 mil 68 mil 28 mil 26 mil The pad pattern with copper spreading shown in Figure 2 improves the thermal area of the drain connections (pins 1,2,3,6.7,8) while remaining within the confines of the basic footprint. The drain copper area is 0.0054 sq. in. or 3.51 sq. mm). This will assist the power dissipation path away from the device (through the copper leadframe) and into the board and exterior chassis (if applicable) for the single device. The addition of a further copper area and/or the addition of vias to other board layers will enhance the performance still further. An example of this method is implemented on the Vishay Siliconix Evaluation Board described in the next section (Figure 3). THE VISHAY SILICONIX EVALUATION BOARD FOR THE SINGLE 1206-8 The ChipFET 1206-08 evaluation board measures 0.6 in by 0.5 in. Its copper pad pattern consists of an increased pad area around the six drain leads on the top-side—approximately 0.0482 sq. in. 31.1 sq. mm—and vias added through to the underside of the board, again with a maximized copper pad area of approximately the board-size dimensions. The outer package outline is for the 8-pin DIP, which will allow test sockets to be used to assist in testing. The thermal performance of the 1206-8 on this board has been measured with the results following on the next page. The testing included comparison with the minimum recommended footprint on the evaluation board-size pcb and the industry standard one-inch square FR4 pcb with copper on both sides of the board. |
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