TPS54335A: tps54335a belt can't afford to load

Part Number:TPS54335A

sir:

 I use WEBENCH circuit design . VIN=12V  VOUT=5   IOUT=3A. But in fact, tps54335a  belt can't afford to load. the PH, BOOT,VOUT waveform as follow . Q1:What causes it  Q2: the  bootstrap capacitor value must 0.1 μF ? if change it,what will happen. (my English is not very good)  Thank you for your support.