Wawa:
This has been discussed before.
Fig.13 on page 12 from the TPIC6B595 datasheet has a diagram of the fet output stage.
The 50volt zener diode is part of that active clamping circuit.The disadvantage of darlington arrays like the ULN2803 could be saturation voltage.
Leo..
There is a limit to the avalanche energy the FETs can take, if you can calculate what that motor
stores you can work out if its safe or not - I know I'd rather not have 50V noise all over the place
interfering with other circuitry for no good reason though.