Power Electronics

Power Converter Makers Take Silicon Route

While power semiconductor makers have pushed the level of integration on a single chip for decades, recent activity suggests that power supply manufacturers are also entering the arena to push the level of power density and performance of dc-dc converters to newer heights. Two new products out of power supply makers Power-One and Vicor have seemingly affirmed our long-standing thesis that the functionality of the dc-dc converter will eventually be fully integrated on a single piece of silicon, noted senior analyst Todd Cooper in a research report published by Stephens Inc., a financial servicing company. The research analyst expects more power supply manufacturers to join the fray.

Targeting point-of-load (POL) converters designed for the emerging intermediate bus architecture, Camarillo, Calif.-based Power-One recently launched a highly integrated dc-dc converter in a multichip-module (MCM) format. Andover, Mass.-based Vicor Corp. has also crafted a new power system architecture called factorized power architecture or FPA. For that, Vicor has developed a family of building blocks labeled V.I chips (VICs). In essence, it is Vicor's version of the distributed power architecture.

Tiny Converter

Called maXyz, Power-One's first product in its new line is X3015P, which integrates 22 power semiconductor and layout-critical passive components to deliver 15A of output current at 5V from a 10-mm × 12-mm footprint. Only 1.5 mm high, this tiny device uses a single land grid array (LGA) package (see photo). Consequently, you can mount it on the bottom side of a host pc-board, reducing critical space consumption on the topside.

According to Power-One's Chairman and CEO Steve Goldman, “The X3015P is a significant strategy shift for us that involves the development of an advanced-technology power-conversion product utilizing a fabless semiconductor business model.” He added, this patent pending semiconductor-like product catapults Power-One into a new market segment, the silicon-based power conversion and management. Toward that goal, Power-One has partnered with outside foundry and packaging service providers.

Housed on a LGA substrate are the synchronous buck PWM controller, driver circuits and two low RDS(ON) MOSFETs along with associated passives (Fig.1). In fact, the controller and driver are on a single chip, according to executive vice president Dave Hage. Hage added, the topology uses synchronous rectification wherein the controller, driver and the FETs are all optimized for minimal switching losses to achieve maximum efficiency. As per the data sheet, it offers 95% efficiency at 3.3V output and 5A current with 5V input. However, it derates at higher temperature. Because the fixed-frequency of the dc-dc converter is programmable, it allows the user to select optimum inductor and capacitor, he continued. The switching frequency can be varied from 300 kHz to 500 kHz.

Although, the X3015P packs all the necessary components in a single package, it still requires a few external components to complete the dc-dc converter design. Besides an inductor and a few I/O capacitors, it requires three external resistors — one for frequency variation, another for output voltage adjust, and a third one for current limit. The X3015's input voltage range is 3Vdc to 6Vdc, while the output can be adjusted from 0.75Vdc to 4Vdc with up to 15A capability. The output voltage accuracy is ±1.2%. And the converter boasts current density in excess of 80 A/in.2.

Meanwhile, Power-One is also readying members with higher input capability to expand its POL converter offerings. While X3015P is designed for 5.0V and 3.3V input buses, a 12V version is also in the making. It will offer similar output as the first introduction, but with 17A current capability. In addition, the company plans to offer an online design tool that will enable users to pick right passives around the part to meet the final specifications. A prototype reference design kit that includes an X3015P mounted on an evaluation board for testing is being offered to selected customers. The X3015P is undergoing life and reliability tests, and is expected to go into production next month. In quantities of 10,000 pieces, the X3015P is priced at $7.00, which drops to $5.50, in lots of 100,000.

New Distribution Scheme

Vicor's proprietary FPA comprises a pre-regulator module (PRM) and a voltage transformation module (VTM). The control ICs incorporated in these modules are designed internally by Vicor engineers. In this modified distribution scheme (Fig.2), the PRM takes an unregulated input, such as the 48V from a telecom system, and produces a well-regulated output, which the developer prefers to call factorized power bus. The VTM converts this bus voltage to levels required by the load with efficiencies as high as 97%. Additionally, VTM provides input to output isolation. And switches at 3.5 MHz to respond to dynamic loads much faster.

Depending on the load current, output voltage, available space, and system cost, you can configure the PRM and VTM modules in a variety of ways. For instance, a single PRM can power multiple VTMs in an open loop configuration to generate multiple voltages, as you can see in Fig.3(a). If tighter regulation is desired, a single PRM can drive an individual VTM in a closed loop manner, as in Fig.3(b). Thus, if multiple tightly regulated voltages are needed, then multiple PRMs will power multiple VTMs, as shown in Fig.3(c). Also, the design permits multiple VTMs to operate in parallel for higher current or power levels.

PRM's input range is 1.5V to 400Vdc. And its regulated output, which is nonisolated, can go from 0.5Vdc to 400Vdc. In reality, this range is limited to 5:1 in real world product. Likewise, the VTM input voltage range is 2 to 400Vdc with output range of 0.5V to 400Vdc. But, in practice, VTM's input range is limited to 2:1. The modules come in BGA style packages occupying less than 0.25 cu in.

In short, a single VTM can handle 80A up to 2.5Vdc output or deliver less at higher output voltages for a maximum of 200W. To minimize common-mode and differential mode noise at POL, a VTM combines the attributes of zero-voltage, zero-current switched topologies. Thus, a 48V to 12V VTM offers about 50 mVp-p high frequency ripple, which amounts to 0.5% of the dc output. This performance is better than the company's low noise bricks, according to the manufacturer. Vicor prefers to call these building blocks of FPA architecture as VICs.

As per the manufacturer, a 200W PRM or an 80A VTM is priced at $25.00 each in OEM quantities.

Power-One, Camarillo, Calif., www.power-one.com CIRCLE 347 on Reader Service Card

Vicor Corp. Andover, Mass., www.vicorpower.com CIRCLE 348 on Reader Service Card

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