Buck Converters Squeeze into Tiny QFNs

Sep 1, 2006 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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Using its multi-megahertz switching and co-packaged inductor technology, Enpirion has expanded its lineup of integrated buck converters with tiny footprints and high efficiency. Members of the new EP53x2Q family target low-power and portable applications with current ratings of 500 mA, 600 mA and 800 mA. Each buck converter combines a monolithic switching regulator (PWM controller plus MOSFET switches plus compensation network) and a power inductor in a single 5-mm × 4-mm × 1.1-mm QFN (Fig. 1).

The EP53x2Q requires two external multilayer ceramic capacitors to complete a buck converter design. Typical capacitance values are 2.2 µF on the input and 10 µF on the output. This allows a total footprint of 28 mm² for the complete design. Despite this small size, these devices can step down a 3.6-V input with efficiencies greater than 85% at 1.8-V output and approaching 95% at 3.3-V output (Fig. 2). [For comparisons with some other high-frequency switching regulators, see “Multi-Megahertz Switching Gains Momentum,” Power Electronics Technology, April 2006, pages 46-48.] With their ease of use, small size and high efficiency, the buck regulators are being positioned as replacements for linear regulators in portable consumer applications.

As with the company's previous products, the new devices contain a switching regulator fabricated in a CMOS process with a four-layer adder employed to grow LDMOSFETs. The unique design of the MOSFET enables a 5-MHz switching frequency, which in turn allows the inductor to be designed small enough for co-packaging with the switching regulator chip. The high switching frequency also enables fast transient performance. In addition, a typical peak-to-peak output voltage ripple of 5 mV makes the converters suitable for portable applications with sensitive RF subsystems.

The company's earlier products, which were 3-A and 6-A parts in larger IC packages, incorporated a MEMS inductor sitting on a silicon substrate. In the EP53x2Q, the MEMS inductor (a copper spiral) is deposited on a ferrite substrate, which lowers its cost. With the new parts, the company has also moved from the laminate-style package to a leadframe-style package for improved thermal performance. In addition, portions of the leadframe have been etched away to reduce input and output capacitances, lowering switching losses.

The voltage output for the EP53x2Q is programmed using a 3-pin voltage select scheme allowing the designer to choose from one of seven predefined voltages (ranging from 1.2 V to 3.3 V). Alternatively, an external divider may be used to achieve other values at voltages as low as 0.6 V. Furthermore, the voltage select pins can be changed on the fly to implement dynamic voltage scaling. The integrated compensation network affords stability over all operating conditions with 10 µF to 60 µF of output filter capacitance. The input voltage range is 2.4 V to 5.5 V.

Other features include an enable pin that responds to digital levels or V_IN/GND and 100% duty cycle operation for maximum battery life. There are also protection features such as undervoltage lockout with hysteresis, overvoltage and short-circuit protection, and thermal shutdown with hysteresis. In addition to the standard devices with co-packaged inductors, the company also offers versions of the EP53x2Q for use with external inductors.

The EP53x2Q power devices are available immediately. Pricing in quantities of 1000 units is $1.61 for the 800-mA version, $1.55 for the 600-mA version and $1.50 for the 500-mA version.

For more information, see www.enpirion.com.