DRV8701: PH Damaged

Part Number:DRV8701

Hi,

I've been testing the robustness of the driver and I've been impressed so far.  There's only one thing I've had go wrong a couple of times and I'm not sure what causes this.

The PH stops working/ fails if I go from 0-1 or 1-0 while EN is 1.  It's not instant, I can switch it 10-15 times before failure but eventually one direction doesn't drive and the other does.  The chip does get quite hot when the nonfunction direction is selected. 

I would imagine the internal chopping should start it up slow, which it does but it still seems to damage PH.

Thank you,

Mat