Patent ID: 7649330

Claim:
A circuit for controlling the application of pulse-width modulated power to a voice coil motor in a disk drive, comprising: a retract transistor, having a control terminal and having a conduction path for coupling between a capacitor and a first side of the voice coil motor; and; drive circuitry coupled to the control terminal of the retract transistor, for turning the retract transistor on and off in a pulse-width modulated manner during a retract stage; and a recirculation transistor, having a conduction path for coupling between a second side of the voice coil motor and the first side of the voice coil motor, and having a control terminal; wherein the drive circuitry is operable to turn on the recirculation transistor while the retract transistor is turned off, and to turn off the recirculation transistor while the retract transistor is turned on, and the drive circuitry comprises: a sense amplifier, having first and second inputs for coupling across an external sense resistor connected in series between the second side of the voice coil motor and a ground voltage; comparator circuitry, for comparing an amplified voltage from the sense amplifier to at least one voltage limit; and logic circuitry, having an input coupled to an output of the comparator circuitry, and having outputs coupled to the control terminals of the retract transistor and the recirculation transistor, for turning on and turning off the retract and recirculation transistors responsive to the comparator circuitry.