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LM3406: LM3406 Blinking

Ammar shamsi
Prodigy 110 points
Part Number: LM3406

Hi,

 We finalized LM3406 for our an OEM client's 12W Solar Street Light, In the proto everthing was O.K, Now we moved to 500Pcs Pilot.In this lot, some board(around 40%) are working o.k but remaining are having a problem. The problem is LED is not glowing continuously, it just blinks/Flashes continuously every second. The doubtful point is Pin12. As we are using DIM pin for PWM dimming we left this pin open. When we test with Pin12 to +Vbat(12V)  the LED glows continuously for few seconds and the I.C becomes hot and gets damaged. 

Please help.

 

  • 0
    TI__Mastermind 25500 points

    Hello Ammar,

    The VINS pin is high impedance with no internal pullup/pulldown so it should not be left floating. If unused it should be connected to VIN. If it is left floating it will always be in an unknown and varying state which is why you saw the flashing.

    I would need more information. Could you let me know what the input voltage and LED stack voltage is that you are using? What exactly is the circuit with Q4, R21, and another resistor connected to something I can't see for? Are you having issues if you remove Q4? If you can let me know the input/output then I can see if there are any issues with the design. A BOM and layout would be helpful as well if you can provide them.

    Regards,

    Clint