VIN

VOUT

VDx

Driver

current limit

Buck-boost

converter

GREEN

RED

R_EN

G_EN

B_EN

BLUE

GREEN

RED

GREEN

RED

BLUE

GREEN

RED

PWM

100%

80%

BRIGHTNESS

100%

0%

t > Timeout

t < Timeout

100%

80%

100%

MINIMUM

60 Hz

LM3549

SNVS640A – AUGUST 2010 – REVISED MAY 2013

www.ti.com

Figure 18. PWM Timing

FAULT DETECTION

LM3549 can detect several different fault conditions. These are LED open, LED short, thermal shutdown (TSD),

under voltage lockout (UVLO) and buck-boost converter over current protection (OCP). If any of the fault

conditions occur corresponding fault bit is set in the fault register. If fault mask bit is not set also Fault output is

pulled low. Reading Fault register resets its value to zero and sets Fault output to high impedance state.

LED OPEN FAULT

Open fault is generated when at the end of color VOUT is at maximum and no current is flowing through driver

(VDx = 0V). Also OCP fault needs to be low. Open fault can be generated by broken LED or a soldering defect.

Figure 19. LED Open Fault

12

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