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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:

fig 1 vs fig 1

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?

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    \$\begingroup\$ MOSFETs will conduct equally well in both directions, as long as they are switched on. While they cannot block voltage in reverse, this property is still very useful and often exploited in e.g. synchronous buck converters (and motor drivers, as you see here). When not on, the body diode inherent in their construction will still allow current to flow "backwards", but with a diode voltage drop and diode recovery time of course. \$\endgroup\$
    – jms
    Commented Oct 3, 2016 at 7:05

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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:

There is no conflict. Look at the characteristic of a "typical" N channel MOSFET: -

enter image description here

Garishly coloured picture taken from here

With no gate voltage you get the red curve that produces reverse conduction due to the internal parasitic diode (circa 0.7 volts) and breakdown at high forward voltage. With gate voltages the MOSFET conducts equally well with negative drain voltages in that area where the parasitic diode won't be significantly conducting.

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