Power Chips Raise the Bar on Operating Voltage

Jan. 1, 2008
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

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 VF 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.

Voltage Regulators

Another high-voltage part unveiled in December was Intersil's ISL6719 100-V linear regulator. This device, which complements Intersil's recently released 100-V triple output linear regulator (the ISL6720A) is said to handle the functions of up to 15 discrete components. Moreover, the ISL6719's 9-lead, 3-mm × 3-mm DFN package occupies less than half the board space of a discrete solution.

Aimed at a variety of telecom and networking applications, the ISL6719 is well suited for use as a single startup linear regulator in isolated power designs, or as an output bias supply for point-of-load regulators in telecom/datacom applications. Unit pricing for the ISL6719 is approximately $1.25.

Switching regulators are also moving to higher operating voltages. Introduced last month, National Semiconductor's LM5015 is a monolithic, two-switch forward dc-dc regulator that features a wide input-voltage range from 4.25 V to 75 V. Targeting telecom, automotive and industrial applications, the regulator can be used to design either isolated or nonisolated dc-dc converters.

The LM5015 features all of the functions necessary to implement efficient two-switch forward and two-switch flyback power converters with a minimum of external components. The regulator integrates high-side and low-side 75-V n-channel MOSFETs with a minimum 1-A peak current limit. The voltage across the MOSFETs employed in the two-switch topology is clamped to the input voltage, allowing the input-voltage range to approach the rating of the MOSFETs.

The regulator control method is based on current-mode control, providing inherent ease-of-loop compensation and line feed-forward for superior rejection of input transients.

The operating frequency of the LM5015 is set with a single resistor and is programmable up to 750 kHz. Protection features include cycle-by-cycle current limiting, thermal shutdown, undervoltage lockout and remote shutdown capability. Available now, the LM5015 is offered in a 14-pin TSSOP package, featuring an exposed die attach pad. Pricing is $2.05 each in 1000-unit quantities.

Some other parts that were announced earlier in the year are also worth noting. Intersil's ISL8560 2-A buck regulator supports an input-voltage range of 9 V to 60 V with programmable output voltages from 1.21 V to 55 V. A related buck regulator, the ISL8540 has an input-voltage range of 9 V to 40 V with a programmable output-voltage range of 1.21 V to 35 V. Both devices have the capability to manage transient spikes of up to 100 V for 400 ms.

Two other devices are 100-V current-mode buck controllers. One is Linear Technology's LTC3810, a synchronous stepdown switching regulator controller that can directly step down voltages from 100 V to output voltages ranging from 0.8 V to 93% of VIN. This chip device employs a constant on-time valley current-mode-control architecture to deliver very low duty cycles and fast transient response with accurate cycle-by-cycle current limiting without requiring a sense resistor.

Another is National Semiconductor's LM5116, a 6-V to 100-V buck controller that produces a programmable 1.215-V to 80-V output. This device uses the company's emulated current-mode control to overcome the noise susceptibility and duty-cycle limitations of traditional peak current-mode control, by emulating the buck switch current signal.

Going down in the voltage range, Micrel's MIC2130/1 series of high-voltage synchronous buck controller ICs offers a frequency-dithering feature that minimizes EMI and adheres to global EMC standards. Targeted at the industrial, communication, automotive and high-end consumer markets, the controllers operate over an input-voltage range of 8 V to 40 V, generating an adjustable output voltage down to 0.7 V.

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