Power Electronics
9-A Buck Converter and Inductor Fit In Compact QFN

9-A Buck Converter and Inductor Fit In Compact QFN

With its introduction of a 9-A synchronous buck converter, Enpirion extends its portfolio of power converter ICs with copackaged inductors to a higher current level, offering designers a very compact point-of-load power solution. The EN5395QI combines a monolithic buck converter and a bar-style inductor in a 10-mm x 12-mm x 1.85-mm QFN package. The converter accepts a 2.375-V to 5.5-V input.

As with the company’s previously introduced parts, the converter die and the inductor sit side-by-side in the IC-style package. However, the type of inductor used in the EN5395QI is different. The new part uses a bar-type inductor in which copper-strap windings are wound around the core material. In contrast, the existing Enpirion devices employ a high-aspect ratio, conventional wirewound inductor that is self-shielding.

The advantage of the bar inductor is that it permits a higher current rating in a smaller form factor. That reduction in inductor size offsets the increase in die size that was needed to raise the current rating from 6 A, which was previously the highest current rating offered by an Enpirion buck converter. The die used in the 9-A part is larger than in the 6-A model because the higher current rating requires greater die area for the power MOSFETs.
But as already mentioned, the smaller inductor makes up for the larger die such that the EN5395QI comes in the same package as the company’s existing 6-A part. Not only are the footprints the same, but pinouts are as well. So it’s possible, to layout a board for the 6-A buck converter and then upgrade to 9 A by dropping in the EN5395QI. However, the company also plans to introduce a new 6-A device using the bar inductor and that part will come in a smaller package than the existing 6-A converter.

The EN5395QI requires as few as five external MLCC capacitors for a complete point-of-load converter and occupies a total footprint of 250 square mm. The EN5395QI delivers up to 30 W of continuous output, and achieves up to 93% efficiency (see the figure). This performance translates to a power density of over 76 W/in.2 or over 11 W/cm2.

The output voltage of the EN5395QI is programmed using a 3-pin voltage-ID (VID) input, which allows designers to choose one of seven pre-programmed output voltages. However, for designers who need an output that’s not available from the ‘5395, the company offers a second version of the converter—the EN5396QI. The output of that device is programmed using an external resistor divider to any value in the output voltage range (as low as 0.75 V).

For applications requiring higher current, the EN5395QI allows from 2 to 4 devices to be paralleled for up to 36 A of output current. The EN5395QI is designed to meet the precise voltage and fast transient requirements of low-power processors and system-on-a-chip (SoC) devices. With its low-noise PWM topology, the 9-A buck converter is ideally suited for noise-sensitive applications, according to the vendor.

The EN5395QI is available now for general sampling. The device is expected to be released to production in August at which time the company will post the final data sheet for the part. The data sheet that’s available online now (see http://www.enpirion.com/Productdetails.aspx?pid=34) is labeled preliminary. Pricing for the EN5395QI is $8.10 each in quantities of 1000.
For comparisons with some existing parts, see Linear Technology’s LTM4608, an 8-A dc-dc converter that also has a co-packaged inductor and a similar input voltage range (2.375 V to 5.5 V). In addition to its slightly lower current rating, the LTM4608 differs from the EN5395 in that it comes in a larger 9-mm x 15-mm x 2.8-mm LGA package. However, note the differences in efficiency, output voltage range, and the presence of the output voltage tracking and margining in the ‘4608. Also, note the difference in pricing. More details on the LTM4608 are available at http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1424,P37471.

Comparisons can also be made with Texas Instruments’s SWIFT series of monolithic converters. See data for the 9-A rated SWIFT chips, which include the TPS54980, ‘54974, ‘54972, ‘54910, and ‘54973. These are monolithic buck converters with a narrower input-voltage range than the EN5395QI and without a co-packaged inductor. Among other performance comparisons, note the differences in packaging and features such as tracking, and pricing.

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