Power Chips With Magnetics Are Going Mainstream

Jul 1, 2007 12:00 PM
David Morrison, Editor

Only a few years ago, the idea of co-packaging an inductor with a buck-converter die in a standard IC package was quite a novelty. But since Enpirion, a New Jersey-based startup, took that step in the spring of 2004, a few mainline semiconductor companies have followed suit. Moreover, today several others chipmakers appear poised to introduce their own buck-converter ICs with built-in magnetics, though most are coy about their intentions. So, why is this happening now? And does it matter? Should we expect this trend to have much of an impact on power-system design or on the power-component business?

First, consider the developments so far. Enpirion's initial product was a 3-A buck converter in an 8-mm × 12-mm DFN. The company subsequently introduced variations for higher and lower current levels in smaller packaging, but all with about the same 2.4-V to 5.5-V input range. In 2005, Linear Technology introduced a rather different version of co-packaged magnetics, a 10-A buck converter in a 15-mm × 15-mm LGA with a 4.5-V to 28-V input range.

Last fall, Micrel Semiconductor and Fuji Device Technology America unveiled their modules. These 500-mA and 600-mA devices were more in the vein of Enpirion's products in terms of input-voltage and output-current levels, though they seem to employ a standard ferrite or multilayer ceramic inductor rather than a special magnetics design. Switching frequencies were also different. Enpirion's converters were switching at 5 MHz, Micrel's at 8 MHz and Fuji Electric's at just 2.5 MHz.

Although these devices achieve reasonable efficiency, their high switching frequencies and tiny inductors necessitate the tradeoff of at least a few percentage points in efficiency versus what could be achieved with an external inductor. But apparently there are enough space-constrained applications where designers will make that exchange for the smallest footprint. And many of these applications need switchers that can stepdown 5-V or sub 5-V supplies (sometimes from a Li-ion cell) to lower voltage levels.

Some of the vendors cited so far have plans to introduce additional converters with different current levels, better light-load efficiency, smaller size or other benefits. (For more on these developments see Analog Feedback on page 46.)

When asked whether they might be developing parts similar to the ones described above, other power IC suppliers have given elusive responses. Some have told me they have nothing in development or that they're still investigating the topic.

But recent product development suggests more than a passing interest on the part of many vendors. If the 2.5-MHz switching frequency is taken as a point of entry for embedding the inductor, then several companies already are positioned to do so. Maxim Integrated Products, Texas Instruments, Fairchild Semiconductor, National Semiconductor, Advanced Analogic Technologies, ON Semiconductor and Linear Technology all have monolithic regulators capable of switching at 3 MHz or higher. Expect at least one or more of these vendors to introduce a buck converter with a co-packaged inductor in the next year or two.

The emergence of this new class of power ICs isn't likely to reshape the power-component landscape in the near term. Rather, like other advances, it will tend to make the product spectrum more diverse. I expect the new devices also will drive innovations in magnetics design, both conventional types and still-to-come MEMS versions. Even now, magnetics suppliers are expanding their product lines to offer more low-profile power inductors for use at higher switching frequencies.

The critical nature of the magnetics design suggests that this expertise may increasingly be brought into the semiconductor world. That would seem to be one more extension of the system-level approach that IC manufacturers started to adopt years ago. So, could chip makers one day be competing with magnetics suppliers, rather than just collaborating with them on reference designs? Perhaps the relationship will be similar somehow to the way power IC vendors currently compete with power-supply vendors even as they sell chips to them.

However these developments unfold, system designers stand to benefit. Nevertheless, when these equipment designers are architecting their power systems, the “build versus buy” decisions will only be more complex.