DRV8424E: differences with DRV8424P and brushed DC motor speed control

Hello,

I need to drive two DC brushed motors with speed control.

I was looking at DRV8424E/P datasheet:

I know that both DRV8424E and DRV8424P  have an internal PWM (depending on VREF) to limit the inrush current,  but my doubt is about the difference between handling xPH vs. xIN1,xIN2 signals.

1) The DRV8424P is defined as "controlled using PWM interface", so I suppose i can modulate xIN1 and xIN2 signals whereas the xPH must be kept fixed at full logic value (0 or 5V), is this right?

2) Since  DRV8424P  seems not to be not availabe from my supplier, can I use DRV8424E  and adjust VREF voltage to implement dynamic speed control?

3) I know that some ICs adjust VM voltage of H-bridge, depending on the external PWM applied.  In DRV8424E  I see that VM is also used to power internal logic, so I guess it not feaseble here and VM must be kept constant voltage, right? 

Thank you in advance and regards,

Massimo