Ah - shit. I guess I could limit current for each channel to 15mA. Maybe I'd need to sort out something else - I'll have a think.
Out of interest - where did you find out about the 120mA? I had a look at the datasheet (Allegro MicroSystems 2981 datasheet pdf) and couldn't work it out.
The datasheet mentions -500 mA for Iout .. does Iout refer to the total current from all 8 drivers?