Electronic Design

Fully Integrated PSoC Tops Speed, Efficiency Marks

This monolithic dc-dc buck converter crams a controller, MOSFETs, and an inductor into a tiny, low-cost package.

It outputs 3 A of current and 10 W of power, yet it measures 8.1 by 12.5 mm, is 2.2 mm high, and takes up a mere 135 mm2 of pc-board space. In spite of these features, its bill-of-materials (BOM) cost competes with existing products.

All right, enough To Tell The Truth. This mystery guest is the EN5330 power system on a chip (PSoC) from two-year-old startup Enpirion. According to the company, the EN5330 is the world's smallest PSoC and the fastest dc-dc buck converter for point-of-load (POL) applications. With a controller, FETs, and an inductor built in, the chip only requires three external capacitors and a resistor to work. Enpirion says it's the first dc-dc converter with an inductor on-chip.

"We are offering the smallest and fastest dc-dc converter on the market," claims Brett Etter, Enpirion's marketing director. "All you need is an extra 10-µF input capacitor, some 40 to 50 µF for an output capacitor, a small-value capacitor for programmable soft-start capability, and an external ground resistor, and you're all set to go" The external resistor won't be needed in the final version.

The chip comes in a 36-pin, dual flat no-lead (DFN) package. It also will be available in a quad flat no-lead (QFN) package (Fig. 1). Part of Enpirion's planned line of iPower integrated devices, it has a maximum switching frequency of 10 MHz and up to 90% efficiency in addition to the aforementioned output power and current (Fig. 2). Because it takes up just 135 mm2 of pc-board space, OEM users can reduce the pc-board space needed to mount the converter by as much as 70% (Fig. 3).

According to the company, that 135 mm2 of board space is on the development board. This area can be squeezed down further once the layout is optimized on the final board design. An ultra-low-profile device with a height of 1.00 mm is available as well.

Just how did Enpirion manage to do it? "We looked at the constraints involved using standard mainstream processes and developed the circuit design techniques, the architectural layout, and the required materials with that in mind," says Ashraf Lotfi, Enpirion's president, founder, and chief technology officer. "Our objective was to develop a high-performance and highly integrated part at a reasonable cost level the market would accept." The device is made on a deep-submicron CMOS process.

Key technology innovations involved in making the EN5330 include the chip's power FETs, which are five to 10 times faster than other power FETs. Also integrated are a MEMS inductor—the first for a power converter—and a digital power-management control algorithm that allows microsecond-type responses, ultimately lowering overall system power consumption.

The EN5330 accepts an input voltage of 2.375 to 6.5 V and typically operates at 5 MHz. The output voltage is programmable in six steps. Output voltage accuracy is specified within ±3%, and output voltage ripple is specified at 40 mV. The output voltage accuracy specification is actually achieved without trimming the reference voltage. Enpirion plans to trim this accuracy to within ±1%.

Production versions will employ three VID pin-selectable voltage-select lines. Other features include Output Enable and Power OK signals. The device also possesses overcurrent, short-circuit, overvoltage, undervoltage, and thermal-shutdown protection.

A key design challenge was choosing the right magnetic materials for the MEMS inductor.

"There are lots of magnetic material formulations, and most of them (99%) are not manufacturable at a reasonable cost or at a cost acceptable to the power-conversion market," says Lotfi.

"You can make an inductor smaller than ours by using ultra-thin materials, but the materials themselves have power and frequency limitations," he adds. "Most magnetic materials in use today are ferrites where permeability characteristics will roll off as a function of increasing frequency, with the inductance values dropping and losses increasing. We developed a formulation that rolls off at a higher frequency and will take us to 10 and 20 MHz, using an existing mainstream process that makes the planar inductor more easily manufacturable and thus low in cost." The inductor is laid out atop the integrated electronics of the converter chip (Fig. 4).

Enpirion developed a patented digital control algorithm for digital power management (DPM) that's optimized for maximum slew-rate control. The algorithm's response time of a few microseconds is an order of magnitude faster than existing DPM algorithms. The rapid handling of voltage and frequency scaling saves more power.

The company is positioning its converter chip for the rapidly emerging PSoC market. Enpirion views this segment as the bridge between semiconductor component vendors and modular and power-supply manufacturers.

"Semiconductor vendors who make the controllers, FETs, etc., are essentially in one market area, and module and power-supply makers who use those parts are in another," says Mike Laflin, product marketing director. "We're bringing them the best of both worlds with a true PSoC device."

The 10-W, 3-A EN5330 has been sampling since January. Samples of a 20-W 6-A version have just become available. Production quantities for both are slated for the third quarter.

Enpirion offers two power device lines. The iPower line, which includes the EN5330, targets POL applications. The miPower line of converters is optimized for power-sensitive, space-constrained, and high-efficiency applications like digital cameras, cell phones, PDAs, and MP3 players.

The EN5330 costs $4.95 each in 1000-unit quantities. Evaluation boards are also available.

(908) 479-1422

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