VIN

VOUT

VDx

Driver

current limit

Buck-boost

converter

LM3549

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SNVS640A – AUGUST 2010 – REVISED MAY 2013

LED SHORT FAULT

Short fault is detected when VOUT < 1.0V at the end of a color. Short fault is generated when VOUT is shorted

to driver by soldering defect or faulty LED. Driver current limit limits the maximum current. Depending on output

current and positive limit settings, LED short can also generate OCP fault to fault register.

Figure 20. LED Short Fault

TSD FAULT

fault is generated to Fault register when device goes from shutdown mode to standby mode. It is good practice to

reset the fault register by reading it every time after device is set from shutdown mode to standby mode.

UVLO FAULT

Under voltage lock out (UVLO) fault is generated if VIN drops below UVLO level (~2.5V). UVLO sets device to

standby mode. When VIN rises back above the 2.5V device exits UVLO. If control register values were changed

from EEPROM defaults they need to be rewritten to registers because UVLO condition can generate EEPROM

read sequence.

OVER CURRENT PROTECTION FAULT

Over current protection (OCP) fault is generated when positive current limit is active at the end of a color. It is

important to notice that OCP fault is not always set when positive current limit is activated. Positive current limit

can activate during normal operation when buck-boost is adjusting the output voltage to a higher level. OCP can

be caused by short from VOUT to GND, short from driver to GND or if too low positive current limit value is set

for desired output current.

I

capacitance of the bus (typ. ~1.8k). Signal timing specifications are shown in Table 1.

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