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EDNE MAY 2015

Power conversion current change at a given input/output voltage ratio is larger. This allows a faster reaction to a change in output current. There is a drawback when it comes to losses in the system; switching and magnetising losses scale with the switching frequency. For these reasons, the majority of converters still operate at a switching frequency in the range of 2 MHz to 6 MHz. The lower frequencies are typically used for applications with a relatively large input voltage, and a focus on high efficiency. Whereas the higher frequencies have advantages when it comes to the best transient performance; and the smallest total solution size. The next step in the evolution was to use chip scale packaging for power devices. This reduces the size because there is no package as such. The silicon is just covered on top with a thin tape that contains the marking and protects the silicon from mechanical influences. On the bottom where the active circuitry is located, balls are added which form the electrical connections. Chip scale packaging is the smallest possible. The only disadvantage is that the silicon size needs to be large enough to hold the number of balls required for the electrical connections. Figure 2. MicroSIP construction For microprocessors it is common practice to stack the memory on top of the processor or even stack multiple dice on top of each other. Why not do the same thing with the passive components in a switch mode power supply? The TPS82xxx family of devices is going down that route. The passive components are stacked on top of the silicon. However, this is not done directly on the silicon but the silicon is embedded into a PCB, which in turn holds the passive components. Applications that require small solutions typically also care about the volume, not only the area. As such, a solution has to be competitive with discrete solutions with respect to height. The MicroSIP modules in the TPS82xxx family provide a total solution size of 6.7 mm² at a height of 1 mm maximum. This is achieved by packaging the silicon inside a 300 μm (0.3 mm) thick PCB which has the passive components on top and balls similar to WCSP or BGA packages on the bottom. This means the module can be picked, placed and soldered like a BGA package. This allowed shrinking the solution size to roughly half that of a discrete solution; the article continues with an illustration of the difference between the discrete solution and the MicroSIP version Download PDF of Article Find Power conversion on EETsearch 26 EDN Europe | MAY 2015 www.edn-europe.com


EDNE MAY 2015
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