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LM5013-Q1: LM5013 burns!!

Fabio Arcangeli
Prodigy 20 points
Part Number: LM5013-Q1

Tool/software:

I'm having lot of problems using the LM5013-Q1 regulator.
It should be thermal and overload protected and work at least up to 3.5A but with a 2.8A of load, when it's case reach 100°C it burns (with flames!!)
Even if the thermal dissipation is not good, why it's themral protection do not work? How can it generate flames?

  • 0
    TI__Intellectual 1935 points

    Hello Fabio,

    At which condition your device is burning? What are the operating conditions (Vin, Vout, fsw)? Please share your schematic and layout image.

    The device might get damaged due to high voltage stress beyond abs max datasheet limits. Could you please measure the voltage spike between SW pin and the GND pin with probe (set the probe full bandwidth) to check if the damage is caused by the voltage spike? make sure the measurement loop is small to avoid noise coupling.

    Regards,

    Arpita

  • 0
    TI__Intellectual 1935 points

    Hello Fabio,

    At which condition your device is burning? What are the operating conditions (Vout,Vin,fsw)? Please share your schematic and layout image for debugging. 

    The device might get damaged due to high voltage stress beyond abs max datasheet limits. Could you please measure the voltage spike between SW pin and the GND pin with probe (set the probe full bandwidth) to check if the damage is caused by the voltage spike? Make sure the measurement loop is small to avoid noise coupling.

    Regards,

    Arpita

  • 0 in reply to ARPITA NATH
    Prodigy 20 points

    Hi Arpita,

    I attached schematics, PCB and a photo of the burned device.
    It works with 38V max input (28V AC + rectifier bridge and filter capacitor) and 25,2V output, very far from maximum device capability, but I fund a mistake: it has been mounted a 30V diode (SSB43-E3) inspite of the 40V (SSB44-E3), may be this the cause? (with the temperature increasing it can break shorting SW to GND) But in this case why the overload and thermal protections doesn't stop the DC/DC avoiding the burning?

    For a better heat dissipation is better to place the controller toward the center of the board inspite of near the edge?

    Many thanks for your support.

    FabioLM5013 board.pdf

  • +1 in reply to Fabio Arcangeli
    TI__Intellectual 1935 points

    Hi Fabio,

    If the diode damages for voltage stress larger than rated, there might be a short circuit at SW node to GND. When the top FET is turns on, the current rises with a very high slew rate through Vin>top FET>SW>GND. The slew rate of current will be very high, so even before current limit is triggered, the device will get damaged.

     In the case of output short circuit or overload, the current rises with a slower rate comparable to this particular case, because inductor is involved. So, in that case., IC is protected by current limit feature. 

    Regards,

    Arpita

  • 0 in reply to ARPITA NATH
    Prodigy 20 points

    Yes, I tried to use the right diode and now, increasing the load and consequently the temperature, the device reach the temperature limit and start cutting the output without damages.

    Many thanks.

    Fabio