Regulators Embed Inductors to Save Space and Ease Use

Jul 1, 2007 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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Application requirements for compact, easy-to-use voltage regulators with better efficiency than LDOs is spurring the development of a new class of buck-converter ICs. These devices are monolithic switching regulators with inductors included in the IC package. With their very high switching frequencies and tiny inductors, these devices are not as efficient as buck-converter designs optimized using external inductors; nevertheless, they offer a boost in efficiency versus the still pervasive LDOs.

Buck regulators with co-packaged inductors are now available for current levels ranging from about 500 mA to 6 A for inputs up to 5.5 V. That input range accommodates single-cell Li-ion batteries and 5-V intermediate buses.

Available from vendors such as Enpirion, Micrel Semiconductor and Fuji Device Technology America, these converters can generate outputs as low as 0.72 V, while switching at frequencies ranging from 2.5 MHz up to 8 MHz, depending on the device. The style of inductor varies from vendor to vendor with some using multilayer ceramic and others using ferrite types.

The regulators are typically housed in QFN- or DFN-style packages, which have small footprints and low profiles, even below 1 mm. As with other regulator ICs, units from different vendors compete with one another on overall solution size, efficiency over the load range, noise performance, cost and even reliability.

Some regulators switch from PWM operation to an LDO mode to limit the noise at light loads. For battery-powered portable products, some devices offer 100% duty-cycle operation with a PFM mode to maximize light-load efficiency. Most devices offer output-voltage adjustment via external resistors and some allow voltage programming with a VID code. Enable pins and on-chip protection (thermal, overcurrent and undervoltage) are common features.

For applications requiring inputs of 4.5 V to 28 V, and output current levels at 6-A to 12-A or higher, Linear Technology offers its µModule series in an LGA package. Though these parts co-package the inductor, they're rather different from the lower-current models described above. In addition to differences in voltage and current levels, they also have features such as PLL synchronization for low noise, tracking and margining, remote sensing and multiphase capability The family also includes a recently introduced 4-A regulator that's electrically comparable with the other devices in this article, though it switches at a lower frequency (1.25 MHz).

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© 2007 Penton Media, Inc.