DRV3901-Q1: VDRV questions

Tool/software:

Hi team, 

I have some questions for DRV3901-Q1 need your help here. 

1. What is the main function of diode between VREG and VDRV? How we determine whether we should use this diode or not? 

2. How we suggest customer to select tWK_PU time in their application? 

3. Does DRV3901-Q1 support SPI trigger under normal state and change to high or low level signal trigger when MCU fail(SPI not work)? 

Thanks!

Ethan Wen