I have purchased LM3409 Demonstration Board (LM3409EVAL/NOPB, SV600307-001).
I use board for testing purposes for our future product.
Our product will be LED controller for 27V and 1,6A LED stack. At one PCB it will be 40 LED drivers.
We have deal done for 500 pcs of this controllers that mean we will buy 20k LM3409 drivers.
I have big problem with burning LM3409 at power up.
There were some components replaced and I write this component to .pdf attached.
Generally components was replaced for better efficiency and cost optimization.
Demonstration board had switching frequency of 700kHz which I have decreased to 530 kHz, with replaced R1 (15,4k) to 22k.
I also use different MOSFET, Diode, shunt and inductor.
Problem is next:
-> Power supply is 36V. Vout is 27V, Iout 1,6A nominal (Imax 1,8A in final functionality)
-> When I get Demonstration board I have run it and measure switching frequency and efficiency.
-> Then I have started with replacing components and also measuring efficiency.
-> Once at start up LM3409 burned out. I did not know why. There were no short circuit because few times before it work properly.
Result was that MOSFET and LM3409 was burned out. I have replaced and it worked for a while.
-> After few days I was making new measurements with new components (MOSFET and diode). Demonstration board
worked for few times then again LM3409 burned out. Then I have replaced MOSFET and LM3409 and it burned out 3 times in line.
After that I have replaced: shunt, inductor, diode, MOSFET and LM3409 and then it worked.LM3409_Demonstration_Board.pdf
-> Yesterday I was going to measure final measurements with selected MOSFET. At demonstration board I had original MOSFET ZETEX with
custom diode, shunt, cout and inductor, because I wanted to measure efficiency with this set up.
Power supply voltage was set to 36V, supply current limit to 2A, load of 21R. Device was in disabled mode
with jumper places to corresponding position. AND when I have connected to power supply LM3409 burned out! Again. I have replaced LM3409 again and it worked. Then I have replaced MOSFET with DMP6050 and it worked. I have measure efficiency.
-> Today I was going to lower switching frequency. I connected power supply and it worked with load of 15. Then I have added 0R6 resistor in series with 15R and when I connected to power supply LM3409 burned again. FET is OK.
Till now I have burned 10 LM3409 all at start up. Obviously there is something wrong at start up.
I have removed R5 potentiometer. Instead of J1 jumper I have soldered resistor divider of 150k and 12k so at EN pin is 2,66V (@36Vin) and 1u capacitor directly to pin 3 and GND.
Can you give me answer what is wrong?
Problem is because we have PCB in design and we will make 20000 LED drivers and now I have problem that there is very big chance that LM3409 will burn out at start.
I replaced original LM3409 with LM3409HV (see ordering code in .pdf).
Thanks for your answer in front.