The chip's primary purpose is to provide a "soft start" for a motor, preventing current inrush. The triac is controlled by a linear "ramp" from minimum to maximum power. Start rate can be varied from 0.5 sec. to 3 sec, by changing the option bits. The secondary function of the 90805 is proper ignition of the triac for inductive and resistive loads, while keeping the triac's current consumption to a minimum.