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LM3549 Fiches technique(PDF) 9 Page - Texas Instruments |
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LM3549 Fiches technique(HTML) 9 Page - Texas Instruments |
9 / 25 page R_EN G_EN B_EN R_OUT G_OUT B_OUT GREEN RED R_EN G_EN B_EN BLUE GREEN RED GREEN RED BLUE GREEN RED 7.5% 11% 12.5% 7.5% 12.5% 7.5% 11% 12.5% 7.5% 12.5% 60 Hz LM3549 www.ti.com SNVS640A – AUGUST 2010 – REVISED MAY 2013 OPERATION DESCRIPTION LM3549 is a sequential LED driver for portable video projectors. It has three high current low side drivers and a buck-boost DC-DC converter. Only single LED can be enabled at any given time. DC-DC converter quickly adjusts the output voltage to a suitable level based on each LED’s forward voltage. This minimizes the power dissipation at the drivers and maximizes the system efficiency. Figure 15 shows a typical timing of a portable video projector light source. Each frame is divided into 10 individual color sequences. White balance is achieved by adjusting the driver currents. Timing of LM3549 depends solely on the R_EN, G_EN and B_EN inputs. Each driver’s current is set with I2C registers and current levels can be stored to internal EEPROM. After correct current values are stored to EEPROM LM3549 can be used in application without I2C interface. Full frame 1/60Hz 16.66 ms Red Full frame x 7.5% 1.25 ms Green Full frame x 11% 1.822 ms Blue Full frame x 12.5% 2.08 ms Figure 15. Timing Chart CONTROL INTERFACE Even though each driver has its own control input only one driver can be enabled at any given time. If second control is pulled high while previous color is active second output won’t be enabled until the first input is pulled low. This can be seen on Figure 16. G_EN is pulled high while R_EN is still high. G_OUT is not activated until R_EN is pulled low. Next B_EN and R_EN are both pulled high while G_EN is high. When G_EN is pulled low R_OUT is enabled because R_EN has higher priority (Priority order: RGB). Figure 16. Control Signals Copyright © 2010–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3549 |
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