TI's DRV8801 H-bridge has different decay modes, i.e. what happens when the switches are turned off - short the motor (slow decay) or reverse it until the current has decayed (fast decay). They say that synchronous decay / rectification is more efficient than just using the freewheeling diodes for each FET (asynchronous decay / rectification).
However, the (overly simplified?) schematic figures in their application note SLVA321 (March 2009) all show N-channel FETs and thus a conflicting flow of current:
I am omitting the figure of the intermediate phase of asynchronous rectification by means of body freewheeling diodes.
Are they using additional FETs or how does it work?