LMZ21701 's 3.3 V output always be short circuit with ground ?

I use LMZ21701 in a new design and the schematic circuit is refferenced from LMZ21701 data sheet，input power is 12V ，and it's output power is configured 3.3V as the data sheet advised，3.3V is used to provide power to the whole board about 38mm*38mm ，but the 3.3V output is always short  with ground，I have replace the LMZ21701 module five times, it's still easy to spoiled.    what is the problem?? please help!