UCN5804 O/P series diodes

Hey guys,
if you look at the data*** of Allegro's UCN5804 typical application
shows 4 diodes in series from the 4 o/p's to the 4 windings with anode
towards the windings and the cathode towards the chip's o/p .....

im a bit comfused with how this works.....i know the data*** says
sumthing about substrate current but this does not make much sense to
me!!!

how can the o/p from the chip even reach the windings if the diode is
reverse biased???

Thanks
Nav

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