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AD5253BRU100-RL7 Fiches technique(PDF) 26 Page - Analog Devices |
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AD5253BRU100-RL7 Fiches technique(HTML) 26 Page - Analog Devices |
26 / 32 page AD5253/AD5254 Data Sheet Rev. C | Page 26 of 32 APPLICATIONS INFORMATION RGB LED BACKLIGHT CONTROLLER FOR LCD PANELS Because high power (>1 W) RGB LEDs offer superior color quality compared with cold cathode florescent lamps (CCFLs) as backlighting sources, it is likely that high-end LCD panels will employ RGB LEDs as backlight in the near future. Unlike conventional LEDs, high power LEDs have a forward voltage of 2 V to 4 V and consume more than 350 mA at maximum brightness. The LED brightness is a linear function of the conduction current, but not of the forward voltage. To increase the brightness of a given color, multiple LEDs can be connected in series, rather than in parallel, to achieve uniform brightness. For example, three red LEDs configured in series require an average of 6 V to 12 V headroom, but the circuit operation requires current control. As a result, Figure 45 shows the implementation of one high power RGB LED controller using a AD5254, a boost regulator, an op amp, and power MOSFETs. The ADP1610 (U2 in Figure 45) is an adjustable boost regulator with its output adjusted by the AD5254’s RDAC3. Such an output should be set high enough for proper operation but low enough to conserve power. The ADP1610’s 1.2 V band gap reference is buffered to provide the reference level for the voltage dividers set by the AD5254’s RDAC0 to RDAC2 and Resistor R2 to Resistor R4. For example, by adjusting the AD5254’s RDAC0, the desirable voltage appears across the sense resistors, RR. If U2’s output is set properly, op amp U3A and power MOSFET N1 do whatever is necessary to regulate the current of the loop. As a result, the current through the sense resistor and the red LEDs is R RR R R V I = (8) R8 is needed to prevent oscillation. In addition to the 256 levels of adjustable current/brightness, users can also apply a PWM signal at U3’s SD pin to achieve finer brightness resolution or better power efficiency. |
Numéro de pièce similaire - AD5253BRU100-RL7 |
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Description similaire - AD5253BRU100-RL7 |
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