Electrical – Backlight LED Boost Converter testing

I don't mean to be rude, but read the freaking manual. You will save yourself and others lots of time.

Let me tell you this, and to anyone who reads this. When you get a new part and datasheet at minimum skim the whole thing, become familiar with it. You should do this before you even consider laying it out on a PCB. I was in the same boat you were a few years back, and then I made sure I read the whole datasheet a few times through. You will get a better more intuitive feel for how the part works. You will have fewer mistakes and a better career. Also if you run into a problem, read the datasheet then look for applications guides. Then if your sure you have the circuit within all circuit guidelines and it still isn't functioning correctly then contact the company. I got lazy the other day and missed an absolute maximum rating, the circuit functioned during functional testing. A company rep caught it, I felt bad.

And I quote:

OUTPUT OVER-VOLTAGE PROTECTION A simple circuit consisting of an external zener diode can be implemented to protect the output and the LM3410 device from an over-voltage fault condition. If an LED fails open, or is connected backwards, an output open circuit condition will occur. No current is conducted through the LED’s, and the feedback node will equal zero volts. The LM3410 will react to this fault by increasing the duty-cycle, thinking the LED current has dropped. A simple circuit that protects the LM3410 is shown in Figure 18. Zener diode D2 and resistor R3 is placed from VOUT in parallel with the string of LEDs. If the output voltage exceeds the breakdown voltage of the zener diode, current is drawn through the zener diode, R3 and sense resistor R1. Once the voltage across R1 and R3 equals the feedback voltage of 190 mV, the LM3410 will limit its duty-cycle. No damage will occur to the LM3410, the LED’s, or the zener diode. Once the fault is corrected, the application will work as intended.