Our requirement was to create a LED driver circuit to power 12 strings of 7 LEDs from a 12V DC supply with a nominal current of 20mA per string.
Using the STEVAL-ILL035V1 Development board data for PCB layout guidance and the LED7708 design tool spreadsheet for component selection we successfully built a prototype driver PCB and produced firmware to setup the on-board registers and control the LEDs for our application.
Initial results were good and all appeared to be working as expected until we noticed that after a random period (5 to 10 minutes) the LEDs would go off completely and wouldn't recover normal operation untill the device was disabled (DEVCFG0.DEN = 0) and then re-enabled.
When the LEDs go off the boost converter goes into a skipping mode of operation but no errors are indicated either from the XFLT pin or the status registers.
After disabling/enabling the device, the LEDs would come back on normally but would then go off again some time later. Interestingly this would be a much shorter period than the initial illuminated period. I'm unsure if this indicates a heat issue but temperature measurements (taken at 25DegC ambient) of the LED7708 device and PCB don't show anything outside expected running temperatures.
If the LED brightness is lowered from 100% to below 75% or the number of enabled strings is reduced this appears to have an effect on how long they will stay illuminated. Sometimes they will stay on indefinitely at 50% dimming.
If anyone has had issues like this in the past, maybe you could tell us about your experiences or possible solutions you can suggest.
Many Thanks,
Shapeshifter
