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Driver Chips Target High-Brightness LEDs
With the growth of high-brightness (HB) LEDs in automotive, signage and other applications, requirements for high-current drivers are rising and more chip vendors are taking notice. Now, in addition to companies such as Supertex, which has long specialized in the development of driver chips for HB LEDs, companies such as Maxim Integrated Products and Linear Technology are offering drivers capable of supplying the hundreds of milliamps required by these power-hungry LEDs.
The new LED driver chips address power requirements in automotive and signage lighting as well as those in avionics, architectural, display and navigation. Moreover, these ICs begin to address the power needs in general lighting — the so-called holy grail of LED lighting.
Maxim's recent introduction is the MAX16800, a 350-mA adjustable LED driver that drives one or more strings of HB LEDs. Because of its wide input-voltage range (6.5 V to 40 V), the MAX16800 is well suited for automotive, commercial and industrial applications. The wide input range allows the chip to withstand automotive load-dump transients.
The MAX16800 specifies a load accuracy of ±3.5% to maintain consistent brightness across multiple light assemblies. Also, the device's low-dropout pass element (0.5 V typical) and low-voltage (204 mV) current-sense reference minimize power dissipation in the system. The driver enables PWM-controlled dimming of the LEDs either by pulsing the enable input or by pulsing VIN. Wave-shaped circuitry generates soft-edges on pulse loads and reduces EMI during PWM dimming.
A fixed 5-V output regulator delivers up to 4 mA of load current for low-power applications over the input-voltage range. The MAX16800 comes in a 5-mm × 5-mm 16-pin QFN and requires two small ceramic capacitors and a sense resistor. Unit pricing for the IC starts at $0.99 per 1000.
Another new device is Linear Technology's LT3474 fixed-frequency stepdown 1-A LED driver. This chip is distinguished by its wide 400-to-1 dimming range achieved using the company's PWM circuitry. According to the company, this range avoids the color shift normally associated with LED current dimming. The driver operates from a 4-V to 36-V input range, and high-output-current accuracy is maintained over a load current range of 35 mA to 1 A.
An adjustable switching frequency of 200 kHz to 2 MHz enables the use of small external passives. In a typical application, a small inductor, four small ceramic capacitors, a Schottky diode, and a frequency-setting resistor complete the LED driver circuit. The LT3474 comes in a 16-lead TSSOP.
Power Chips and Software to Pass $40 Billion by 2010
A recently released report from Business Communication Co. (BCC) forecasts that the growth in the combined markets of semiconductor and software components for power supply and power management will reach $43.5 billion in 2010. BCC's projection is based on the application of an average annual growth rate (AAGR) of 9.6% to the estimated value of these combined markets for 2005, which is $27.54 billion. In the report, called “RGB-324 Power Supplies and Management for Electronics: Semiconductor Devices and Software,” power management software is considered supplemental software that places digital equipment into low-power states during periods of inactivity. At present, this software market is small, but BCC projects that it will grow rapidly in the next few years, reaching $130.5 million by 2010.
The various market segments within the scope of the report include power management ICs, voltage regulators, transistors and power management software. According to the report, the market for semiconductor components experienced a downturn from 2003 into 2004. However, that market improved in the second half of 2004 and is expected to have grown substantially by 2010. The ICs represent nearly 20% of the revenue of the semiconductor market. According to BCC, worldwide demand for high-quality grid power is expected to drive growth for voltage regulators. Transistor growth will likely be fueled by general high demand from across the electronics industry, especially from the industrial, telecommunications and consumer products segments. The report shows that a highly probable trend during this growth will be the displacement of conventional bipolar transistors by MOSFETs and IGBTs.
|Worldwide Market||2002||2003||2004||2005E||2010||AAGR% 2005-2010|
|Power Semiconductor Devices||18,608.9||21,287.5||25,782.7||27,507.1||43,508.9||9.6|
|Power Management Software||9.3||14.9||20.6||33.0||130.5||31.6|
According to the report, market leaders in the power supply and management semiconductor industry include National Semiconductor (the market leader for ICs), Texas Instruments, Linear Technology, ST Microelectronics, Infineon Technologies, Renesas Technology, International Rectifier and Fairchild Semiconductor (the market leader in power transistors).
BCC's report contains the description and future market impact of each major type of power supply and management semiconductor device. Applications and associated vertical markets are also discussed for both these devices and power management and supply software components. There is also coverage of major technological issues, industry trends, the regulatory environment and the value chain for these combined markets. For more information, visit www.BCCresearch.com.
Identifying Processors Enables New Line of Digital Power Converters
At last month's Digital Power Forum in Boston, several power supply vendors unveiled their development of digitally controlled nonisolated and isolated dc-dc converters. These include power converters from Artesyn Technologies, Astec Power and Delta Electronics. While Artesyn and Astec have taken the PMBus route, Delta uses its proprietary communications/control bus to achieve results.
Unlike others, Artesyn's PMBus-compliant nonisolated point-of-load (POL) programmable 20-A converter DPL20C uses a hybrid approach to offer the benefits of analog and digital technologies. Consequently, it uses an off-the-shelf analog PWM controller and an inexpensive 8-bit microcontroller to handle the digital configuration, monitoring and diagnostic capabilities accessible via the PMBus interface. Most microcontrollers offer SMBus/I2C interface. Hence, it was not difficult to implement PMBus by mapping the commands into the nonvolatile memory of the microcontroller, said Todd Hendrix, Artesyn's vice president of marketing.
Some key features include programmable output voltage from 0.6 V to 5.5 V, programmable sequencing, tracking and margining, real-time monitoring of voltage, current and temperature, with automatic warning of fault conditions and the ability to source/sink 20 A of load current, along with differential remote sensing. It offers a library of 45 executable PMBus commands, as well as Windows-based GUI supporting a variety of PC interfaces.
Likewise, Astec Power, an Emerson Network Power company, has unwrapped a PMBus-compliant digital power converter. Unlike Artesyn, Astec uses a digital PWM controller that combines the advantages of a digital signal processor (DSP) and systems management/control and fast response of a traditional microcontroller. The digital controller employed in Astec's isolated DTX dc-dc converter was co-developed with another fabless design house with the control algorithm developed at the University of Florida. Besides enabling designers to digitally control parameters like output voltage and startup sequencing via a PC with an easy-to-use graphical user interface, Astec's DTX converter also offers patent-pending features such as self-diagnostics and an efficiency optimizer.
The first member of its fully isolated, fully digital-mode dc-dc converter is DTX42K48, which accepts dc input from 36 V to 75 V and offers output from 0.96 Vdc to 1.44 Vdc, with output power up to 50 W. According to Bharat Shah, Astec Power's vice president of marketing for dc-dc business, more than 81 PMBus commands are embedded in this module. The digital PWM controller employed in Astec's DTX converter is expected to be available as a standard part from the fabless design company that was involved in the design of this controller.
Delta, on the other hand, has tapped Primarion's latest digital multiphase PWM controller to ready a 30-A dc-dc converter that addresses the ever-growing needs of increased current and power densities in networking applications. Measuring 0.5-in. × 0.5-in. × 1-in., Delta's DXP 30 is designed to operate from an input voltage of 7 V to 11 V and provides adjustable output voltages from 0.8 V to 2.5 V in digitally defined step resolutions of 1.62 mV. It boasts a usable (55°C, 200 LFM) current density of 60 A/in2 and a power density of up to 216 W/in3.
Lab to Develop Li-ion Batteries for HEVs
Johnson Controls (www.johnsoncontrols.com) has launched a Li-ion battery development laboratory in Milwaukee, to create advanced power-storage solutions for near-future hybrid-electric vehicles (HEVs). The facility features a “dry room” and an array of highly specialized tools and equipment for designing, developing and testing power-storage and power-management concepts based on Li-ion technology. The laboratory facility and development equipment were installed at a cost of approximately $4 million.
Because of their performance advantages, Li-ion batteries are expected by many in the industry to replace the nickel-metal-hydride batteries that are currently used in HEVs. A number of automakers are already developing HEVs that employ Li-ion batteries. According to Hideo Takeshita, vice president of the Institute of Information Technology (www.iit.co.jp), HEVs powered by Li-ion batteries are expected to begin low-volume production in 2007, with high-volume production of such vehicles expected the following year.
Low-Threshold MOSFETs Build Nanowatt Circuits
Advanced Linear Devices' (ALD's) NanoPower MOSFET arrays offer a new level of accuracy in controlling gate-threshold and subthreshold voltage characteristics. With gate-threshold voltages as low as +0.20 V (with ±0.02-V tolerance), these small-signal transistors can reduce the power consumption of common analog circuits into the nanowatt range. This device family includes quad or dual n-channel matched-pair enhancement-mode MOSFET arrays packaged in PDIP and SOPs.
Although not developed specifically for power applications, these devices can enhance power management in power supply designs by implementing functions like ultralow-power oscillators or differential amplifiers. Other possible uses include current sources, current mirrors and analog multiplexers. Available now, the NanoPower MOSFETs are priced starting at $0.67 each in 100-piece quantities.
The low-threshold voltages and tolerance range of the MOSFETs are made possible through ALD's Electrically Programmable Analog Device (EPAD) technology, which allows these MOSFETs to be precisely trimmed at the factory. Once trimmed, the device voltage and current characteristics are stored indefinitely in the chip. Trimming is achieved through a series of software-controlled injected voltage charge packets to a floating gate structure. For more details on EPAD, see www.aldinc.com.