Low-power pulse-width-modulated retract of disk drive actuator

Abstract

A disk drive system including retract logic for control of the voice coil motor in a retract operation, in which the voice coil motor positions the read/write head actuator arm in a safe place in a loss-of-power event, is disclosed. The retract logic includes circuitry for controlling the application of power to the voice coil motor from an external capacitor in a pulse-width modulated manner. Current from the capacitor is coupled to the voice coil motor in a drive phase of the pulse-width modulation cycle, and is recirculated through the voice coil motor in a complementary phase of the pulse-width modulation cycle. The recirculation is accomplished by a recirculation transistor that is smaller than the pull-down transistor used in the drive phase. The pulse-width modulation is controlled by sensing a voltage across an external sense resistor connected on the low side of the voice coil motor, by a common mode circuit including resistor chains, biased from a voltage common to a bias voltage of the sense amplifier.