Four- and Eight-Channel CCFL Controllers Reduce External Components by 50% and BOM Cost by 20% in LCD TVs and PC Monitors
| Note to Editor: The DS3988 (8-channel) and DS3984 (4-channel) controllers can be used to implement simple, low-cost controller circuits for multiple CCFLs in LCD TV and monitor backlights. Compared to the typical full-bridge solutions offered by the competition, the DS3988/DS3984's push-pull architecture uses half as many external components and reduces the total BOM cost by 20%. The low component count simplifies the circuit design and
PC-board layout, and further lowers costs by minimizing assembly costs and PC-board size. |
DALLAS, TX-October 13, 2005-Dallas Semiconductor (NASDAQ: MXIM) introduces the DS3988 (8-channel) and DS3984 (4-channel) cold cathode fluorescent lamp (CCFL) controllers for liquid crystal display (LCD) TVs and PC monitors. The DS3988/DS3984's unique push-pull architecture uses half the external components of traditional designs and reduces the total BOM cost by 20%. The devices' low component counts, moreover, simplifies the circuit design and PC-board layout, and further lowers costs by minimizing assembly costs and PC-board size.
LCD Complexity and Cost Issues
CCFLs provide the backlight light source for the vast majority of LCD applications. LCD TVs use between 6 and 40 CCFLs each, depending on the size of the TV. An LCD monitor typically uses 2 to 8 CCFLs. Given this amount of CCFLs, the backlight inverter circuit is a key design and cost element for both LCD TVs and monitors. The DS3988 and DS3984 circuits employ a simplified design architecture that uses a single integrated controller to control multiple lamps. Component count, board size, and manufacturing cost are thereby reduced. This, in turn, is a significant step toward reducing the price and hence, broadening the appeal and market reach of LCD TVs and monitors.
Benefits of the Unique Design Architecture
The DS3988 and DS3984 utilize a push-pull, nonresonant architecture which requires only half the components of the typical full-bridge LCD solutions offered by the competition (O2 Micro, MPS). Both controllers have many programmable capabilities that allow them to be customized for a specific application. Each part includes individual lamp feedback and control, extensive fault monitoring capabilities, independent onboard oscillators for both lamp and dimming frequencies, and a programmable soft-start profile.
Multiple DS3988/DS3984s can be easily cascaded to control larger numbers of lamps. For maximum lamp control, each channel can be used to drive a single CCFL using only seven low-cost external components per channel. For more cost-sensitive applications, each channel can be used to drive multiple lamps. The devices can be optionally synchronized with external lamp and/or dimming frequency sources.
The DS3988/DS3984s provide feedback per channel, which ensures tightly regulated lamp currents for equal lamp brightness and maximum lamp life. In addition, the lamp waveforms are highly sinusoidal with little or no DC offset, thus providing excellent electrical efficiency (up to 85%) and further extending the lamp life. The integrated fault-monitoring circuitry checks for failure-to-strike, open-lamp, shorted-lamp, and overvoltage conditions. While ensuring a safe and reliable system, that monitoring also eliminates the need to discretely implement those functions. The onboard oscillators are accurate to ±5% over the supply voltage (4.5V to 5.5V) and temperature (-40°C to +85°C) ranges. This high level of accuracy provides the tight tolerance needed to avoid visual artifacts that can occur when the backlight frequencies interfere with the display’s row and frame rates. Finally, the programmable soft-start minimizes audible transformer noise by allowing the burst dimming soft-start to be tailored to the specific transformer-lamp combination.
Prices for the DS3988 start at $1.95 and $1.20 for the DS3984 (50K-up, FOB USA).
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