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.

registers and current levels can be stored to internal EEPROM. After correct current values are stored to

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

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