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audio/videoZONE Products for the week of February 11, 2008
Fairchild Semiconductor Says…
FAN7316/17: Highly Integrated CCFL Backlight Inverter Drivers for LCD Backlighting
Parts Simplify Design, Increase Reliability and Reduce Total System Costs
Fairchild Semiconductor introduced the industry’s most integrated CCFL backlight inverter drive ICs providing space and cost savings, superior system reliability and simplified design for N-N half-bridge, push-pull, and P-N full-bridge LCD backlight inverter designs. The FAN7316 and FAN7317, featuring a wide input voltage range, and built-in open lamp protection (OLP) and open lamp regulation (OLR*) circuit, eliminate up to 30 external components in four lamp circuit inverter designs compared to similar devices on the market. These highly integrated CCFL backlight inverter drive ICs also feature selectable dimming polarity and analog and burst dimming functions, which simplify design and speed time-to-market.
“Fairchild’s FAN7316 and FAN7317 offer the industry’s most comprehensive protection functions resulting in superior system reliability. By reducing the number of components, these devices specifically address the ever-growing need to reduce overall system cost in LCD designs,” said Jay Lee, director of Fairchild’s Lighting product line.
EN-Genius Says…
The story here is integration. The FAN7316 brings on-chip the open-lamp protection circuitry with four comparators for four different lamps. The input voltage capability of up to 24 V also means that no external regulation or dc-dc conversion will usually be needed.
The open-lamp protection uses the voltage across a small resistor on the return side of each of the lamps which, of course falls to zero when the lamp open-circuits. The same voltages are taken and commoned, with diode protection, as the feedback voltage. The FAN7317 has a slightly wider input voltage range (to 25.5 V) and adds open-lamp regulation detection circuitry and pMOSFET driving capability.
The on-chip 6 V precision regulation voltage is held within 25 mV line regulation and 60 mV load regulation. Under-voltage lockout is a comparison against 4.5 V allowing turn-on if the input voltage exceeds 4.5 V. An enable input is also provided requiring a turn-on voltage exceeding 2 V. There is also a thermal shut-down and soft-start.
The PWM burst dimming oscillator has a nominal frequency of 300 Hz with a 10 nF capacitor. It can be varied by the value of that capacitor but it is recommended not be less than 120 Hz, to avoid visible flicker. Analog dimming can also be used, with either positive or negative polarities. With recommended component values the normal output frequency is about 49 kHz with a striking frquency of 64 kHz.
The normal architecture of the inverter driver is a n-n half-bridge, but push-pull can also be driven.
Fairchild has done a very nice job in reducing the component count in a four-lamp backlight and the products have been priced to sell.
The FAN7316 and FAN7317 are in production in Pb-free SOIC-20 priced at $1.48 and $1.55, respectively, in 1000-piece lots.
Data Sheet
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