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Electronic Design


Standalone Li-Ion Battery Charger Boasts 90% Conversion Efficiency
The MAX1737 standalone battery charger can manage one to four lithium-ion (Li-ion) cells. It features better than 0.8% battery-regulation voltage accuracy and 90% conversion efficiency. A complete state machine safely controls the charging sequence. Its step-down, switch-mode, dc-dc converter uses a small external dual N-channel FET as a power switch and a synchronous rectifier to provide up to several amperes of accurate charging current.

This device's internal voltage regulator powers the IC, permitting operation up to 28 V. It can work with a duty cycle of up to 98%, producing a very low dropout voltage. Also, it regulates the voltage set-point and charging current with two loops working together to transition between current regulation and voltage regulation. A built-in safety timer, meanwhile, automatically terminates charging once a selectable time limit has been reached.

Packaged in a 28-pin QSOP and specified for −40°C to 85°C, the MAX1737 starts at $2.85 in 1000-unit quantities.

Maxim Integrated Products, 120 San Gabriel Dr., Sunnyvale, CA 94086; (800) 998-8800;

Closed-Loop DC-AC Inverter Powers Backlit LCDs With 12 CCF Tubes
The MA series dc-ac inverter provides up to 40 W with 85% to 95% efficiency to LCDs backlit by up to 12 cold cathode fluorescent (CCF) tubes. Its power boost feature—a logic signal that increases inverter output by up to 30%—suits it for cold operating environments while enhancing CCF-tube warmup at startup. Measuring 6.03 by 1.78 by 0.67 in., the MA series' form factor is optimized for large, 15- to 20-in. displays.

Its tube current control is via closed-loop design, suiting it for flat-panel displays, large desktop monitors, and conference room displays. Also, its hybrid open frame/encapsulated construction ensures high performance and durability while maintaining light weight. With flicker-free, 1% to 100% brightness control, the inverter can be used in applications with required dimming.

In 500-unit quantities, the models in the MA series cost $58.45 each. Delivery is four weeks ARO.

Endicott Research Group Inc., P.O. Box 269, 2601 Wayne St., Endicott, NY 13760; (800) 215-5866;

Compact Bridge Rectifiers Designed For High-Volume Manufacturing
The DF series of compact, 1-A, single-phase, full-wave bridge rectifiers has been designed with unique power-to-volume ratios for greater power density in high-volume industrial and consumer electronic devices. These devices are compatible with all standard pc-board assembly and soldering techniques. Soldering can be performed below 24°C to minimize solder oxidation without losing meniscus and fillet formation. These rectifiers also are suitable for soldering between 250°C and 260°C for eight to 10 seconds.

These bridges offer stable operation between −55°C and 150°C. Their package has high thermal conductivity in an electrically insulated, UL-approved case. Junction-to-case thermal resistance measures 60°C/W. Maximum repetitive peak reverse voltage ranges from 50 to 1000 V. Made with glass-passivated die, they're encapsulated in a four-pin through-hole (D-70) or a surface-mount (D-71) dual in-line package. Through-hole devices are shipped in tubes, while surface-mount devices come in tape-and-reel.

In 10,000-unit quantities, the DF series rectifiers cost $0.42 each.

International Rectifier, 233 Kansas St., El Segundo, CA 90245; (310) 252-7105;

Microstepping Drivers' DMOS Outputs Decrease Power Dissipation
The A3972 and A3973 full-bridge microstepping PWM motor drivers include DMOS (all N channel) outputs for decreased power dissipation and higher peak-current capability, compared to other bipolar drivers. These serial-controlled drivers are based on the ABCD3 power integrated-circuit technology, which combines low-voltage CMOS logic, bipolar control circuits, and power DMOS transistors on a single chip.

Designers can set the load currents via the serial port with two 6-bit linear digital-to-analog converters (DACs) in conjunction with a reference voltage. The 6-bit control provides maximum flexibility in torque control for a variety of step methods, from microstepping to full-step drive. Load current is set in 1.56% increments of the maximum value. Synchronous rectification circuitry lets the load current flow through the low RDS(ON) of the DMOS output driver during the current decay.

The A3972 is available in a 24-lead "batwing" DIP package. It costs $2.65 in 50,000-unit quantities. The A3973 comes in a 24-lead DIP and in an SOIC package. In 50,000-unit quantities, the A3973SLB costs $2.15.

Allegro MicroSystems Inc., 115 Northeast Cutoff, Box 15036, Worcester, MA 01615; (508) 853-5000; fax (508) 853-5049;

MOSFETs Give Vehicle Applications Low On-Resistance Totals
A series of TrenchFET power MOSFETs provides designers with options for forthcoming vehicle applications where higher-voltage standards already are in use. According to their manufacturer, these four devices set on-resistance records. Featuring 100-V operation, the SUP85N10-10 (TO-220) and SUB85N10-10 (D2PAK) models have a 10.5-mΩ on-resistance. Meanwhile, the 75-V SUP85N08-08 (TO-220) and SUB85N08-08 (D2PAK) sport an 8-mΩ on-resistance.

All four TrenchFETs can handle up to 85 A. With 100- and 75-V options, designers can use maximum breakdown voltage or minimal on-resistance as the key factor in their designs. A fifth device with a 25-mΩ maximum rating suits applications where a higher level of on-resistance is acceptable. The SUD40N10-25's 100-V breakdown voltage was combined with a 40-A maximum current rating and surface-mount DPAK packaging.

Samples and production quantities are now available. Larger orders require six- to eight-week lead times. OEM quantity pricing starts at $2.02.

Vishay Intertechnology Inc., 63 Lincoln Hwy., Malvern, PA 19355-2120; (610) 644-1300; fax (610) 296-0657;

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