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LM3492-Q1: LM3492-Q1 open circuit damage

tony li61324
Intellectual 500 points
Part Number: LM3492-Q1
Other Parts Discussed in Thread: LM3492EVAL,

Hi Tier

     LM3492-Q1  use process is as follows（tools LM3492EVAL ）。

     power on LM3492EVAL, work normally， open LED load， Connect  LED load，power off LM3492EVAL . 

   The device is damaged after power supply. Work normally after the replacement of the device。

    This damage is 100% reappearance。

     

  • 0
    TI__Mastermind 25500 points

    Hello Tony,

    What is the timing here? You open the load for some time and then reconnect it and it works fine until you turn the power supply off? If so does the power supply pull the input voltage down quickly and actively when it is turned off? If the input is pulled down too quickly you could have VIN fall below VCC or some other pin which could reverse bias internal diodes and cause damage.

    I would also check various pins when you disconnect/connect the LED load to see if any of them are exceeding abs max due to the transients. If you have long leads to the LEDs the extra parasitics could make the transients even worse. But in general if it works fine after connecting the load but not after turning it off it is more likely there is something about the power down. Are you using the EVM as-is or did you make modifications? What are your VIN, Vout, and LED string currents?

    Thanks,

    Clint

  • 0 in reply to Clinton Jensen
    Intellectual 500 points

    Thank you for your reply！

    Vin 12V . alone 6 string  LED. Normal operating current is 0.15A,The current of the damage is 1A.

    Details are as follows：

    1、Dim1 and  Dim2 connected together

    2、LT3755-2 no damage in case of load disconnect。

  • 0 in reply to tony li61324
    TI__Mastermind 25500 points

    Hello Tony,

    The two devices are quite different, it's possible that reconnecting is dumping too much energy into the linear elements. So you could try reducing the OVP level with FB to reduce the energy. But a disconnect to reconnect really isn't a typical type of operation. An open string generally means catastrophic damage to the string so it will not reconnect. In any case it is nearly impossible to diagnose a damaging event without the ability to probe pins (most likely Ioutx pins) to see if they are violating an abs max rating during the event.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Intellectual 500 points

    Thank you for your reply！

    Disconnect to reconnect really isn't a typical type of operation，But this happens occasionally in the car.

    I will check Iout wave shape.

     

  • 0 in reply to tony li61324
    Intellectual 500 points

    tony li61324 said:

    Thank you for your reply！

    Disconnect to reconnect really isn't a typical type of operation，But this happens occasionally in the car.

    I will check Iout wave shape.

     

    Change the FB1 and FB2 adjustment OVP to solve the problem