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LED Driver ICs Forum Discussions

j_oehmen
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Moderator 10 replies posted 5 replies posted 10 questions asked
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What needs to be considered? Why may my DC-DC converter not start up?
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j_oehmen
Moderator
Moderator 10 replies posted 5 replies posted 10 questions asked
Moderator
LITIX Power devices are using FBH pin for short-to-ground detection and current sensing. The DC-DC converter will not start up as long as the voltage at FBH is below 2V.

Some topologies like boost to ground the voltage at FBH automatically rises above 2V at FBH when an input voltage is applied when the LEDs are directly connected to the output capacitor. Therefore the DC-DC automatically and quickly starts.

When having topologies like SEPIC or when having a dimming switch at the LEDs, the voltage at FBH has to be pre-biased (e.g. by a diode Dpol and a resistor Rpol from IVCC to FBH - see application diagrams in the datasheet). Then the power up time depends on the time constant of Rpol and the output capacitance Cout. The power up time can be minimised by minimizing Rpol. However, this is limited by the maximum output current at pin IVCC.

Take a look at the LITIX Power page for more information

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j_oehmen
Moderator
Moderator 10 replies posted 5 replies posted 10 questions asked
Moderator
LITIX Power devices are using FBH pin for short-to-ground detection and current sensing. The DC-DC converter will not start up as long as the voltage at FBH is below 2V.

Some topologies like boost to ground the voltage at FBH automatically rises above 2V at FBH when an input voltage is applied when the LEDs are directly connected to the output capacitor. Therefore the DC-DC automatically and quickly starts.

When having topologies like SEPIC or when having a dimming switch at the LEDs, the voltage at FBH has to be pre-biased (e.g. by a diode Dpol and a resistor Rpol from IVCC to FBH - see application diagrams in the datasheet). Then the power up time depends on the time constant of Rpol and the output capacitance Cout. The power up time can be minimised by minimizing Rpol. However, this is limited by the maximum output current at pin IVCC.

Take a look at the LITIX Power page for more information
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