Hi,
I can add a little information here...
I can state that it is a fact that there are many power converters out there
that do not use an 'extra' diode in parallel with the MOSFET, and depend
entirely on the integral body diode to take care of the back emf of any
inductive loads. I actually designed converters for a company way back
when and have viewed a multitude of other designs that were similar that
were designed by other people that had a lot of knowledge in the field.
The converters ranged in power from 500 watts to about 10,000 watts
(not all were MOSFET designs however).
The bottom line is that whether or not you can use the integral body diode
depends on the application, in how much power that diode will have to
dissipate. If you look on any data sheet you will find that that particular
diode has a rather high forward voltage, much higher than an external Schottky
would have for example. This means that the transistor using the internal diode
has to dissipate an extra amount of power, not only while the thing is in
conduction, but also when the diode is in conduction, which increases the total
power dissipation of that one little package (even if the forward voltage of
the internal diode wasnt higher than normal). This is probably the biggest
factor in determining if you can use the internal diode or not.
Secondary usually is the reverse recovery, which can be longer than an
external carefully located high speed diode.
The extra power dissipation has to be carefully examined relative to the application.
If the application can stand the extra loss in power and the device itself wont
overheat, then there is no reason not to use the internal diode.
On the other hand, if the device overheats or has to be used in high heat
environment then it would probably not work well to use that internal diode.
Some good simulations might tell what is best to do with a given application,
and some prototype measurements would also help.
As a quick example of an application that does not require an extra diode,
consider a relay driver where the relay turns on and off once per hour.
The integral body diode sees a current spike once per hour that lasts
probably 1ms or maybe even 10ms, but after that it has almost 60 minutes
to cool back down. Adding an extra diode would really be silly here.
On the other hand, a very high speed H bridge may benefit from adding
extra diodes because doing that, if not anything else, moves some of the
heat out of the transistor package and therefore keeps it cooler.
A careful analysis has to be made and some prototype measurements
would verify the need for any extra diodes.
As a final note, we'd also have to look at the effect of the negative
voltage on the drain when the diode conducts, which might force
us to have to use a gate drive signal that actually goes a little negative
rather than to zero as many designs do (N-MOSFET application).