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LM3410: LM3410

ASB
Intellectual 405 points
Part Number: LM3410

We are using LM3410 to control LED backlight brightness by using analog PWM with following circuit topology.  

we are seeing failures with LM3410 (burned IC) under following two conditions

1-     When C71 is installed the additional capacitance damages LM3410 with load present (LEDs are plugged in).  When capacitance is set to  4.7uf (removing C71), the circuit works as intended.   

2-     With C71 removed, When following circuit is powered without any load (no LEDs plugged in) LM3410 is damaged. 

Both failures require replacing LM3410.   

  • 0
    TI__Mastermind 28655 points

    Hello,

    For number 1:

    What inductor are you using?  What is your output voltage?  Is there a reason for so much capacitance?

    Try placing a diode across L1 to see if it stops, anode to Vin, cathode to SW.  Large enough to carry the charge current of the 4.7 uF output capacitors when power is first applied.

    For number 2:

    Look at 8.1.1.7 and Figure 14 of the datasheet.  This is a current regulator, if there is no load the voltage will rise until something conducts.  This circuit pulls up on FB when the voltage gets too high.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Intellectual 405 points

    Thanks Vout is at 14V max.   for Number 1 if I reduce the capacitance to 4.7uF that may not require the diode that you are suggesting

    for Number 2 I left out some circuit which was not on the same page.  here is the complete circuit.  On power up the FB will see some voltage even if there is no load present.  Can you please explain what voltage level would damage on FB pin would damage the IC?  

  • 0 in reply to ASB
    TI__Mastermind 28655 points

    Hello,

    Absmax on the fb pin is 3V.  Also I don't see the overvoltage circuit on the fb pin.  Your added circuitry will not prevent open LED string output overvoltage which will damage the LM3410.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points

    Hello,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue.
    If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Best Regards,