IC Package Houses Complete POL DC-DC Converter

May 1, 2004 12:00 PM
By Ashok Bindra, Editorial Director, Power Electronics Technology

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Power supply developer Enpirion (Bloomsbury, N.J.) is one step closer to packing a complete high-performance nonisolated dc-dc converter on a single semiconductor chip. Combining clever design and advanced CMOS process with a microelectromechanical system (MEMS)-based inductor, the company has packed a complete high-efficiency dc-dc converter in a single semiconductor package. Presently, the MEMS-based inductor is on a separate silcion die. Exploiting advances in CMOS process technology and junction isolation, Enpirion has developed a complete converter with integrated PWM controller and power MOSFETs on the same CMOS chip.

Combining junction isolation with proprietary process, the circuit achieves good noise immunity between the controller and the power circuits. On-chip functions include PWM controller, gate driver and two power MOSFETs, a p-channel and an n-channel, along with protection features (see the figure). The compensation network is implemented with discrete passives.

However, the MEMS-based inductor is a separate entity. Thanks to a 5-MHz switching frequency, the MEMS inductor fits inside a miniature IC package like the DFN. The MEMS inductor uses an iron-based alloy that is plated on a silicon substrate. The magnetic core is on the top and bottom of the copper spiral, giving superior high-frequency and saturation characteristics. This inductor offers excellent performance to over 10 MHz. The result is a turnkey IC package with a standard TSSOP footprint.

Designed for use in point-of-load (POL) applications in servers, PCs, laser printers, set-top boxes and telecom equipment, the integrated iPOWER system requires only three external capacitors and a resistor to complete the nonisolated synchronous buck dc-dc conversion solution. While the three capacitors include small input and output ceramic capacitors and a soft-start capacitor, the resistor sets the output voltage.

The switching frequency made possible by this design is higher than previously possible, and the innovative circuit design techniques enable designers to achieve speed without compromising efficiency of the converter.

The EN5330 — the first member of Enpirion's iPOWER system line of POL converters — comes in a dual flat no-lead (DFN) package that covers just over 100 mm² of board space. The entire dc-dc converter can be placed in as little as 135 mm² of single-sided or 102 mm² of double-sided board space. With a height profile of 2.2 mm, it delivers efficiencies up to 90%.

The nominal input voltage range for the converter is 2.375 Vdc to 6.5 Vdc, which permits operation from 2.5 V, 3.3 V and 5 V rails. The output voltage is selected using a 3-pin combination of 1s and 0s. The voltage-mode feedback control loop uses low-noise PWM control scheme. Up to 3 A (maximum 10 W) of output power can be drawn from this converter.

The VID selectable output voltage ranges from 0.8 V to 3.3 V with an option for an external voltage divider. The output voltage regulation is within ±2% accuracy over line, load and temperature. Also, the converter is protected against overcurrent, short circuit, overvoltage, undervoltage and thermal shutdown. Furthermore, the soft-start circuit prevents the in-rush current when the converter is powered up. The power good signal indicates whether the output voltage is within 90% to 120% of the required command voltage.

In addition to the standard 36-pin DFN package, it's available in 40-pin QFN and lead-free package options. Slated to go into production in the third quarter, pricing is $4.95 each in 1,000-piece quantities.

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