Hopefully fixed - 8 more to go

So far I've managed to kill 5 of these PT4115 LED drivers, and I don't think that I've abused them - at least when compared to what I've done to other devices that survived no problem.

The failure mode is very consistent. Either it stops working altogether (no more switching, output switch permanently open) or the output switch is permanently closed and the LEDs suffer over-current.

Common to both manifestations is that the DIM pin shows unusually low resistance (about 6Ω) to GND. This makes me believe that this pin gets trashed somehow. Therefore I will test if adding a Zener + dropper resistor will help to protect the chip. Voltage clamping at 5V1 definitely works, so lets see how things go.

Adding a Zener + resistor is the way to go. No more premature demise.