High-Voltage Power MOSFETs Lower RDS(ON)
STMicroelectronics has introduced the first devices built using the company's second-generation multiple drain mesh (MDmesh) high-voltage power MOSFET technology. Particularly suited to switch-mode power supplies (SMPSs), power factor correction (PFC) circuits and power adapters, the transistors reduce on-resistance by up to 40%. This enhancement increases efficiency and system reliability, significantly reducing component costs when compared with first-generation MDmesh devices. The new MOSFETs are ideal for power supply applications in the 90-W to 1000-W range.
The improved performance of ST's MDmesh technology is the result of an innovative drain structure in which the drain is implemented as an array of partitions with vertical p-type strips, as an extension of the body, aligned with thin horizontal n-type source strips. In addition to very low on-resistance, this drain structure results in excellent dV/dt and avalanche characteristics.
In this latest generation of MDmesh technology, MDmesh II, further enhancements of the p-strip array have delivered a reduction of up to 40% in the RDS(ON) value compared to the previous MDmesh generation, without sacrificing tight control of its temperature dependence. At the same time, further optimization of the gate finger and oxide layer in the overlaid horizontal source strips ensures perfect control of the internal gate resistance and intrinsic capacitances.
Devices based on MDmesh II also achieve lower switching losses. A controlled gate internal resistance results in reduced delay times and, consequently, faster switching times. In addition, tightly controlled intrinsic capacitances guarantee low crossover time and a low gate charge, improving SMPS efficiency through simpler and cheaper gate-drive circuitry.
For example, the STP25NM60N has an efficiency of 98% at 230 Vac with an output power of 250 W, when tested with an L4981-based 300-W PFC circuit. The improvement in efficiency reduces the size of the heatsink required, while the MOSFET's high-frequency operation allows use of small magnetic components.
STMicroelectronics is offering a number of MOSFETs based on MDmesh II technology, including 500-V, 140-mΩ devices, 500-V, 380-mΩ devices, and 600-V, 170-mΩ devices, housed in TO-247, TO-220,TO-220FP and D2PAK/I2PAK, and DPAK packages. Available now, unit pricing ranges from $1.40 to $1.70 in 1000-piece quantities. For more information, see www.st.com.
Power Supply Vendors Ranked
Recently released rankings of the top merchant power supply manufacturers by sales reveal continued gains by Taiwanese manufacturers as well as some effects of consolidation in the industry. According to data provided by Micro-Tech Consultants (Santa Rosa, Calif.), two Taiwan-based vendors — Delta Electronics and Lite-On Technology — are now among the top five power supply manufacturers in terms of worldwide sales.
In the latest rankings based on worldwide sales in 2004, Delta Electronics maintained its second-place position from the previous year by achieving global sales of $1753 million, while Lite-On moved into the top five with $680 million in sales, earning a fifth-place ranking. In cracking the top five, Lite-On replaced Tyco Electronics Power Supply Division, which had recorded sales of $760 million in 2003. Another change occured in fourth place with U.S.-based Eaton/Powerware ($775 million in 2004) taking the spot previously held by U.K.-based Invensys plc ($1210 million in 2003). Meanwhile, Emerson maintained the No. 1 spot with worldwide sales of $2140 million in 2004. At the same time, U.S.-based American Power Conversion held on to third place with sales of $1700 million in 2004.
These sales figures reflect sales of embedded power supply products sold to OEMs for integration within their products as well as external power supply products sold to telecom service providers. Power supply products included ac-dc and dc-dc power supplies, accessory/ancillary products and services related to power plants or power conversion, and batteries used in conjunction with the power equipment. All sales numbers are approximate values.
|Ranking||Manufacturer||Approximate Sales (Millions of Dollars)|
|3||Tyco Electronics Power Systems Div.||$425|
|9||Acbel Polytech Inc. (API)||$113|
|12||Transistors Devices Inc.||$100 to $105|
In terms of North American sales, Micro-Tech's rankings indicate that C&D Technologies, which was not listed among the top 15 the previous year, climbed all the way to fourth place with 2004 North American sales of $195 million. That gain resulted primarily from acquisitions, as C&D Technologies grew by purchasing Celestica and Datel.
Other newcomers to the top 15 ranking of vendors by North American sales included Hipro, Acbel Polytech Inc. and Sony (see the table on page 13). For more information, see www.micro-techco.com.
Power Modules Deliver High Current Density
Multiphase control, thermally enhanced MOSFET packaging and multiple sets of output pins are among the tools used to develop point-of-load power modules (POLs) that achieve as much as 80 A/in.3 of current density. The POLs, which are the newest members of the PTHxx family of nonisolated power modules from Texas Instruments, deliver 50 A (PTH12040) and 60 A (PTH04040) of output current.
As with other members of the PTHxx family, these modules provide Point-of-Load Alliance (POLA) compatibility. In other words, “interoperable” second-source versions of these modules will be offered by other supplier members of POLA. Other POLA members are expected to begin announcing their 50-A and 60-A power modules shortly.
Offered in 2.05-in. × 1.05 in. (nom.) through-hole or surface-mount packages with a 0.357-in. (max.) profile, these modules include features such as TI's Auto-Track, which allows the outputs of multiple modules to track one another or a common voltage during power-up and power-down. The PTH12040 operates from input voltages of 8 V to 14 V, and supplies up to 50 A of output at 0.8 V to 5.5 V. The PTH04040 accepts input voltages from 2.95 V to 5.5 V and delivers as much as 60 A at 0.8 V to 3.6 V. These POLs operate with up to 96% efficiency.
In the case of the PTH12040, the full 50 A is available at the maximum output voltage of 5.5 V, implying a power delivery of 275 W. However, this performance is subject to thermal considerations and customers may need to derate their modules based on the level of airflow and the maximum ambient temperature in the applications. With a modest 200 LFM of airflow, the PTH12040 will deliver 50 A at ambients up to 70°C. This performance was achieved with a 12-V input and 3.3-V output. Similarly, the PTH04040 delivers the rated 60 A of output across all voltages in the 0.8-V to 3.6-V range, subject to thermal considerations. In the coming months, the company also plans to introduce SIP versions of these units.
According to Don Matthiesen, product marketing manager for TI's Plug-In Power products, the biggest challenge in developing the 50-A and 60-A POLs was thermal management. “The primary feature that gives us the ability to put so much power in such a small package is a three-phase synchronous buck topology,” he said.
The three-phase design enables the heat to be dissipated across three pairs of high-side and low-side output switches. These MOSFETs are housed in thermally enhanced SO-8 packages such as the LFPAK or PowerPAK. In addition, there are separate output and ground pins for each of the three phases. This pinout, which is the company's own design rather than a standard, enables much of the POL's heat to be conducted into the pc board.
With each phase switching at 1 MHz, and the phases spaced 120 degrees apart, the converters achieve an effective switching frequency of 3 MHz. The high switching frequencies help reduce the size of passive components within the modules to achieve a low profile. In addition, the use of flat wire in the inductors helps limit the size of these components, which are the tallest parts on the POLs.
Currently available, the PTH12040 and PTH04040 modules are priced at $35 each in quantities of 1000. For more information, see www.ti.com/sc05113.
Thick Film Circuits Print on Heatsink
TT electronics IRC Advanced Film Division has developed a technique to produce custom thick film circuits and assemblies that allow high current-carrying traces (up to 100 A) to be printed onto ceramic substrates for power hybrids or solid-state relay substrates.
“By using these custom thick film circuits, design engineers can integrate current sense resistors with values as low as 2 mΩ directly into the power-hybrid substrate, which is not a possibility with direct-bonded copper,” said Tom Morris, applications engineering manager for IRC Advanced Film Division. “With this unique design, the circuits can be printed directly on a heatsink, eliminating the additional costs and processes of connecting a heatsink to a power substrate.”
According to Morris, the copper-fired thick films allow different types of circuits, including thermistors and temperature sensors, high-voltage and pulse-withstanding circuits to be combined on one board.
Typical applications for the custom thick film circuits and assemblies are solid-state relay substrates, power amplifiers and power supplies, thermo-electric coolers, water-level sensors and high-brightness LED circuits.
Because most applications are custom, pricing and lead times are available upon request. Assemblies of outboard components are also available from IRC. For more information on custom thick film, see www.irctt.com.
Ceramic Capacitors Withstand Extreme Heat
AVX is developing a range of capacitors designed for high-temperature applications, such as underhood sensors in automotive designs and equipment used in oil exploration. Manufactured with an X8R dielectric material, which has a capacitance variation of 15% between -55°C and 150°C, the capacitors are ideal for use in applications generating temperatures up to 150°C.
“The development of the X8R ceramic capacitors was driven by the needs of our customers who couldn't find capacitors that consistently met the requirements of their demanding high-temperature applications,” said Tim Hollander, AVX product manager.
Available in standard as well as automotive AEC-Q200-qualified parts, the X8R ceramic capacitors offer three options for termination systems: tin, FLEXITERM and conductive epoxy for hybrid applications. They are available in voltages ranging from 25 V to 50 V with capacitance tolerances of ±5%, ±10% and ±20%. Pricing starts at $0.03 in quantities of 10,000. For more information, see www.avx.com.