Sunnyvale, Calif.—Maxim Integrated Products' MAX8729 is a fully integrated controller optimized to
drive multiple cold-cathode fluorescent lamps (CCFL) used in LCD monitor and TV applications. Using a topology that the company touts as unique, the controller works in a resonant mode during striking and switches over to a fixed-frequency mode after the lamps are lit to ensure reliable striking and operation under all conditions while reducing electrical stress on the transformer.
The MAX8729 drives external MOSFETs typically used in applications where one power stage drives four or more CCFL tubes in parallel. The chip's half-bridge inverter, consisting of two external n-channel power MOSFETs, minimizes component count while providing near a sinusoidal drive waveform over the entire input range. The MAX8729's PWM design features a 10:1 dimming range. CCFL brightness can be set with an analog voltage on the device's control (CNTL) pin.
Synchronization and phase-shift features for both the switching and PWM frequencies facilitate daisy-chaining multiple MAX8729s. The chip's internal 5.3-volt linear regulator powers the MOSFET drivers and most of the internal circuitry. The switching and PWM frequencies are adjusted with external resistors. Phase-shift select pins, PS1 and PS2, can be used to program up to four different phase shifts, ultimately allowing the user to link up to six MAX8729s.
The MAX8729 is available in a 24-pin QSOP. A preliminary datasheet for this product is available at www.maxim-ic.com/PRGraphics/PRPDF/MAX8729DS.pdf. Prices start at $4.53 each (1000-up, FOB USA). A preassembled MAX8729 evaluation kit with recommended external components is available to
reduce design time.
Maxim Integrated Products, 1-800-998-8800, www.maxim-ic.com