AL8843 LED Driver Problems

[will_raymo2000]

Hello,

My aim is a 2A constant current LED driver for some grow lights for some chilli plants I'm growing this year. I selected the AL8843 chip (https://www.diodes.com/assets/Datasheets/AL8843.pdf) having had good experiences in the past with the AL8805.

I followed the circuit in the data sheet and modelled my pcb on the schematic and layout of the evaluation board (https://www.diodes.com/assets/Evaluation-Boards/AL8843EV1-User-Guide.pdf).

The LEDs I bought are XM-L2 chips from CREE (bought through RS so the real deal), having seen flashlight drivers driving them at 2A or more on tiny heatsinks I chose 2A for mine on a chunky aluminium heatsink profile.

Assembled a pair of the drivers and thoroughly checked them for any shorts or solder bridges - all good. I am powering them from a 24V chassis mount Mean Well PSU capable of 5A. Configured the LEDs in 2 strings of 5 in series with one driver for each string. Assuming a forward voltage of ~3.1V per diode that worked out at 15.5V nominal output voltage. I punched those figures into the calculator provided by Diodes Inc which can be seen below.

I connected up one driver with one string - got a flash then nothing. The full input voltage is presented at the output but the LEDs are only dimly lit with less than 2mA being drawn. Assumed too much current so removed one of the current sense resistors to make an output current of 1000mA but still no joy. It seems to have killed the first LED in the chain, on checking the rest of the LEDs they all illuminate on the diode test mode of my multimeter but I don't want to connect them again without knowing what caused it.

Does anyone have any experience with what might be going on here? I have a multimeter but no scope unforunately so can't see whats going on at that level. I'm assuming a problem with my layout maybe but not sure. Theres no chance of the LEDs being over driven that quickly is there?

EDIT: Just realised none of the parts showed up on the schematic so here goes;
L1 - 68uH 2.1A Saturation
C1 & C2 50V X7R
C3 100nf 100V X7R
C5 & C6 1uF 100V X7R
R1 & R2 0R1 1%
Diodes are all B360B-13-F as per the eval board

Wiring between LEDs and supply wiring all in 25swg I think (although I havent got the label on it anymore )

[stefanh]

I think the capacitors are bit low in value for the rectifier.

[will_raymo2000]

Turns out that the thermal pad clearance to the pins of the AL8843 were too close and had bridged without me seeing. So the LED string got a full blast of unregulated 24v - woops!

Since being a bit more careful in assembly I have had 3 of these boards running 16 hours a day for a week without issue

[tlwEEVblog]

Hello-  I saw your schematic and pcb and wondered if I could get a copy of each of the files?

Thanks,
Tim