A data storage device is disclosed comprising a spindle motor configured to rotate a disk, wherein the spindle motor comprises a plurality of windings. The windings are commutated based on a commutation sequence while applying a driving voltage to each winding, wherein the driving voltage comprises an operating amplitude during normal operation. When a supply voltage falls below a threshold, the spindle motor is configured into a power generator by at least reducing the amplitude of the driving voltage to substantially zero and then incrementally increasing the amplitude of the driving voltage by at least two steps toward the operating amplitude.