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LM22678-Q1: Regulator immediately blows up

Part Number: LM22678-Q1

I built a power supply following the schematic generated by webench, but it draws a very high current from source and blows up almost instantaneously when switched on. It must be something very obvious, but I can't see it at the moment. Any help debugging the circuit would be very much appreciated.

The schematic from webench (designed for Vin 22.6 to 26.4, Iout = 3A) is this one:

And this is mine

And this is the relevant part of the layout. For testing the regulator output is disconnected from its load.

Here is a picture of the board, the red circle marks the spot where (I believe) the IC broke and smoked. I checked with a multimeter and there are no obvious short circuits.

What can be so wrong? Thank you for helping


  • Hello

    One major problem I see it that the EN pin can not be connected directly to VIN.  There is a ~7V Zener diode

    on this input.  Connecting EN to VIN would cause an un-limited current to flow in this Zener diode.

    You can lift up the EN pin after you solder in a new device to test again.

    See section 7.3.1 of the data sheet.  

    There are a few things in the PCB layout that should be addressed:

    1. In general, try to avoid the use of thermal reliefs.  Use direct connections to power pins and components. 

        This includes VIN, SW, GND, Cin, Cout, Cvcc, Cboot, and L. 

        Thermal reliefs will add unnecessary inductance that can cause unexpected device behavior.

    2. Try to use more top ground plane to connect the various power components.  Additional ground plane

        will also help with thermal management.  It is probably best to connect pin 4 directly to the ground tab.

       This is easy to do when you remove your direct connection to the EN input.


  • Thank you so much, I disconnected the Enable pin and now the regulator is working perfectly! I will also follow your suggestions about layout for the next PCB revision.

    I am really amazed by the promptness and quality of your answer, you have been super helpful.