Method of operating hard disk drives, corresponding control circuit, hard disk drive and processing device

A control circuit configured to operate a voice coil motor (VCM) in a hard disk drive, the VCM configured to be driven based on a value of a back electromotive force (BEMF) of the VCM reconstructed as a function of a voltage drop indicative of an intensity of a current flowing towards the VCM detected by an amperometry resistance, the BEMF of the VCM being reconstructed as a function of the voltage drop via a first gain value determined as a ratio of a first VCM resistance to the amperometry resistance, the control circuit comprising:

• retract logic circuitry configured to be coupled to the VCM and to, during a retract phase:
• produce a calibrated gain value indicative of a second ratio of an actual VCM resistance to the amperometry resistance by applying a correction factor to the first gain value;
• and
• drive the VCM continuously based on a reconstructed value of the BEMF of the VCM, reconstructed by applying to the voltage drop the calibrated gain value.

A hard disk drive, comprising:

• at least one voice coil motor (VCM);
• and
• a control circuit configured to operate the VCM, the VCM configured to be driven based on a value of a back electromotive force (BEMF) of the VCM reconstructed as a function of a voltage drop indicative of an intensity of a current flowing towards the VCM detected by an amperometry resistance, the BEMF of the VCM being reconstructed as a function of the voltage drop via a first gain value determined as a ratio of a first VCM resistance to the amperometry resistance, the control circuit comprising retract logic circuitry coupled to the VCM and configured to, during a retract phase:
• produce a calibrated gain value indicative of a second ratio of an actual VCM resistance to the amperometry resistance by applying a correction factor to the first gain value;
• and
• drive the VCM continuously based on a reconstructed value of the BEMF of the VCM, reconstructed by applying to the voltage drop the calibrated gain value.