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LT3952 to power 450mA 42V LEDs with 4000:1 PWM

Question asked by Alexey.Danilchenko on May 24, 2018
Latest reply on Jun 1, 2018 by Alexey.Danilchenko



I am trying to design a LED driver circuit to drive string of two LEDs at 450mA and 42V (constant current - voltage is maximum from LED specs, in practice it is around 39-40V). The voltage on input is provided by 12V 6A power supply. I have used DC2361A evaluation board schematic as a base but quickly run into problems with the rectifier burning off. The current schematic uses slightly amended circuit with better schottky and new inductor with larger current tolerances from CoilCraft.


My circuit is controlled by MCU and uses the full set of contrast ratio (4000:1) hence the choice of switching frequencies (MCU uses 100Hz at 1:4000):



I now run into a thermal management problem - the LT3952, inductor and shottky get pretty hot (84-85 degrees Celsius). Using single LED (450mA at 21V) keeps the LT3952 at 44-47 degrees Celsius. The board layout I am using follows the guidelines and switching node layout follows the same patterns as DC2361A but on 2 layers PCB. I am looking at some advice how to optimise the temperature - any advise on layout or changes to the circuit would be greatly appreciated.