Disk drive comprising spin down circuitry having a power clamp circuit for enhancing power and braking control

A method of enhancing power management in a disk drive during a spin down mode, the disk drive comprising:

• a disk;
• a head;
• a voice coil motor (VCM) for actuating the head radially over the disk, the VCM having a voltage control input;
• a spindle motor for rotating the disk, the spindle motor comprising a plurality of windings and a rotor rotatable at a variable spin rate wherein the rotor generates a back EMF (BEMF) voltage across the windings proportional to the spin rate of the rotor;
• a plurality of switching elements coupled to the windings;
• switch control logic for generating switch control signals applied to the switching elements for commutating the spindle motor during normal operation and for generating an internal supply voltage from the BEMF during a spin down mode, the internal supply voltage applied to the voltage control input of the VCM for parking the head;
• the method of enhancing power management during the spin down mode comprising the steps of:
• (a) generating a periodic signal, the periodic signal for periodically grounding the windings during the spin down mode in order to boost the internal supply voltage, wherein grounding the windings applies a braking torque to the spindle motor;
• and
• (b) clamping the internal supply voltage to a predetermined level to protect against an over-voltage condition without disabling the braking torque applied to the spindle motor.