LM3492: LM3492 failure at start-up

Hello Artiom,

It looks like that may be where the boost FET is, SW is pins 3 and 4.  The Vout pin is pin 5 which is directly connected to Vout.  Is anything else damaged in the circuit?  Are the LEDs remote connected or local?  As for the reason, excess Vin, excess Vout, saturating inductor, as well as other possibilities.

Best Regards,

Hi Irwin,

Thanks for your response. Speaking about this failure, we had 3 lamps failed at once. It does happen instantly or after couple days of operation. We are reviewing any cause you mentioned. TVS on the input is rated at 45V to blow up, this IC - 67V. No other components damaged in the circuit. If we have some transient voltages, TVS may not respond as quick as IC get damaged (just opinion).

I was able to measure FET transient voltage (SW reference to GND) on repaired board at the time of Power ON (24V battery). OVP is set to 49V, but not sure if that relates to this transient. If that voltage reaches >67V, does IC get damaged instantly?
I could not find any data in the datasheet detailing internal MOSFET's breakdown voltage or avalanche energy it can cope with.

Hello Artiom,

It depends on how much energy however that MOSFET is fairly small and likely would be damaged if the absmax voltage is exceeded.  I'm not sure I understand the waveform above.  Is there an inductor between the source and Vin on the LED driver?  I also don't understand the SW node voltage, seems strange.  What is the sharp step down and then back up?  One thing you can try is to add a diode from Vin to Cout.

I will send you an email.  I'd like to see the schematic as well as what is feeding the input to the LM3492, battery, cable harness and length, and components, etc.

Best Regards,