Power Chips Raise the Bar on Operating Voltage

Jan 1, 2008 12:00 PM
By David Morrison, Editor in Chief

Bringing higher-voltage capability to rectifiers, FET drivers, controllers and voltage regulators is one more way for semiconductor developers to help their customers achieve a more integrated power design. The ability of such components to operate at tens of volts and beyond sometimes means that designers can forego discrete approaches to voltage regulation, while enjoying the benefits of the various protection features that are typically included on chip. A sampling of some recently introduced devices indicates a few of the new high-voltage capabilities available to designers.

A 200-V Schottky

In December, Vishay Intertechnology unveiled the V30200C, a 200-V, 30-A dual trench MOS barrier Schottky (TMBS) rectifier that enables designers to cut costs by using a Schottky diode in place of more expensive synchronous rectification, while achieving similar efficiency and thermal performance. The V30200C is described as the first Schottky rectifier built on TMBS technology with a 200-V reverse-voltage rating. Previous devices built on this technology had reverse-voltage ratings of 150 V or below.

The V30200C, which comes in TO-220AB, TO-263AB or TO-262 packaging, offers several advantages over planar Schottky rectifiers. As operating voltages move to 100 V and above, planar Schottky rectifiers tend to lose their advantage of high switching speed and low forward-voltage drop to a substantial degree.

In contrast, with the proprietary structure of the TMBS, minority carrier injections into the drift region are minimized, which lessens stored charges and improves switching speed. With a low V_F of 0.648 V typical at 15 A and 125°C, and superior switching performance, the V30200C reduces power loss and improves the efficiency of switch-mode power supplies and ORing diodes.

The device is optimized for consumer and computer applications with power ratings from 80 W to 200 W. Samples and production quantities of the V30200C are available now with unit pricing of $0.60 each in 10,000-piece quantities.

FET Drivers

Among the high-voltage ICs introduced last month is Linear Technology's LTC4444, a high-speed synchronous MOSFET driver that operates at input-supply voltages up to 100 V. The chip is designed to drive upper and lower n-channel power MOSFETs in synchronous rectified converter topologies. This driver, combined with power MOSFETs and a dc-dc controller, form a complete high-efficiency synchronous converter.

This driver can source up to 2.5 A with a 1.2-Ω pull-down impedance for driving the top MOSFET and source 3 A with a 0.55-Ω pull-down impedance for the bottom MOSFET, making it suitable for driving high-gate-capacitance, high-current MOSFETs. The LTC4444 can also drive multiple MOSFETs in parallel for higher-current applications.

The fast 8-ns rise time, 5-ns fall time of the top MOSFET and 6-ns rise time, 3-ns fall time of the bottom MOSFET when driving a 1000-pF load minimize switching losses. Adaptive shoot-through protection (which may not be available in competing devices) is integrated to minimize dead time, while preventing both the upper and lower MOSFETs from conducting simultaneously.

The LTC4444 is configured for two supply-independent inputs. The high-side input-logic signal is internally level-shifted to the bootstrap supply, which may function at up to 114 V above ground. Furthermore, this part drives both upper and lower MOSFET gates over a range of 7.2 V to 13.5 V. The chip provides undervoltage lockout for gate-drive voltage.

The LTC4444 is offered in a thermally enhanced MSOP-8 package with prices starting at $1.69 each for 1000-piece quantities.

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