Power Electronics

Components Challenge Power Performance Barriers at APEC

Last week’s Applied Power Electronics Conference (APEC) in Dallas offered vendors a forum in which to unveil a variety of ICs, discrete semiconductors, passive components, and power modules. Among these product introductions, a few stood out as offering break throughs in performance. Such products include an 8-MHz synchronous buck regulator, the first GaN Schottkys, and 8-W surface-mount chip resistors.

Despite the difficulty of achieving high efficiency at high frequencies, the switching frequencies of synchronous buck regulators been rising slowly, but steadily over time in response to demands for small buck converter solutions. Nevertheless, most suppliers of regulator chips have pushed their switching frequencies only up to about 4 MHz. At APEC, Micrel Semiconductor (www.micrel.com) introduced its MIC22856, a 500-mA synchronous buck regulator that switches at 8 MHz.

Aimed at portable applications, this device is a fully monolithic design complete with gate drivers and MOSFETs. The MIC2285 also integrates an LDO to minimize current consumption (IQ) at light loads.

The MIC2285’s exceptionally high switching frequency enables the chip to be used with tiny passives. For example, the reference design calls out a 0.47 µH value for the inductor, which is available as a chip inductor in an 0805 case. The combination of tiny passives with the chip’s 3-mm x 3-mm MLF package produces a complete regulator design in a very small footprint. In addition, the height of the complete design can be less than 1 mm.

Typically, high switching frequencies come at the expense of efficiency. But the MIC2285 achieves reasonably high efficiency under some typical battery operating conditions. For example, when stepping down a single-cell Li-ion battery voltage to 1.8 V, at currents ranging from about 50 mA to 500 mA, the regulator’s efficiency varies between 80% and 90%. At lower load levels, the ‘2285 can be switched to LDO mode, which reduces IQ to 20 µA. The IC operates from 2.7-V to 5.5-V input and produces an adjustable output down to 1 V.

Process technology enables the MIC2285’s high-speed performance. The chip is produced in the company’s 0.5-µm CMOS process, which lends itself to use of a 5-V supply and makes it possible to adjust the regulator’s feedback loop very quickly and minimize deadtime to optimize efficiency.

Currently available, the MIC2285 is priced starting at $1.50 for 1K quantities.

Velox Semiconductor (www.veloxsemi.com/), a spin off from compound semiconductor based components supplier Emcore Corp. (Somerset, N.J.), unveiled 600-V gallium nitride (GaN) Schottky diodes with zero recovery time for power supply applications. According to Velox, these devices are the first GaN Schottky rectifiers on the market. What’s more, the company claims to have achieved performance comparable to silicon carbide (SiC) diodes but at a fraction of their cost.

The GaN diodes are offered in packages similar to silicon and SiC diodes. The company has developed 2-A, 4-A, 6-A and 8-A GaN diodes for applications such as power factor correction, switched-mode power supplies, and freewheeling diodes.

As an alternative to SiC diodes, Velox believes that GaN brings the benefit of Schottky rectifiers to cost-sensitive power supplies where the use of SiC is prohibitively expensive. Right now, only 600-V GaN devices are being offered. However, other voltages and current ratings are in development.

Meanwhile, in the passive component area, BI Technologies (www.bitechnologies.com) announced the BCS8 series of surface-mount current sense resistors. The resistors in this series feature current ratings up to 8 W, yet measure only 6.4 mm x 12.8 mm x 2.5 mm. Typically, flat chip resistors such as these can handle only up to 4 W, so the BCS8 devices will allow some applications that formerly required through-hole current sense resistors to switch to surface mount.

Target applications include battery chargers, servo motor controls, and various power conversion applications. In addition to their high power ratings, the resistors specify a TCRs as low as 30 ppm/ºC.

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