Data storage device reducing spindle motor voltage boost during power failure

Description

BACKGROUND

Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track. A spindle motor rotates the disk at a high speed so that an air bearing forms between the head and the disk such that the head flies just above the disk surface.

When a power failure occurs, it is desirable to park the head before the air bearing dissipates, such as by unloading the head onto the ramp near the outer diameter of the disk. It may also be desirable to finish a current write operation and/or to flush a write cache to the disk prior to parking the head. When the supply voltage is lost due to a power failure, the momentum of the disk spinning generates a back electromotive force (BEMF) voltage across the windings of the spindle motor. Disk drives will typically boost this BEMF voltage using a suitable voltage booster, and utilize the boosted voltage to power the control circuitry used, for example, to finish a current write operation by flushing cached write data to a non-volatile semiconductor memory. The BEMF voltage is also typically used as a current source for the switches of a H-bridge driver that drives the VCM for parking the head (e.g., by unloading the head onto a ramp).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a data storage device in the form of a disk drive comprising a head actuated over a disk, and a spindle motor configured to rotate the disk.

FIG. 1B shows an embodiment wherein a power voltage generated based on the spindle motor is boosted to generate a boosted voltage, wherein the boosting is reduced when the power voltage falls below a threshold.

FIG. 2 shows an embodiment wherein the boosted voltage is reduced based on a linear function of the power voltage.

FIG. 3 shows an embodiment wherein the boosted voltage is reduced by a step decrement based on the power voltage.

FIG. 4 shows an embodiment wherein the boosted voltage is reduced by a staircase of decrements based on the power voltage.

DETAILED DESCRIPTION

FIG. 1A shows a data storage device in the form of a disk drive according to an embodiment comprising a head 2 actuated over a disk 4, a spindle motor 6 configured to rotate the disk 4, and control circuitry 8 configured to perform a power fail operation by boosting 10 a power voltage 12 generated based on the spindle motor 6 to generate a boosted voltage 14, controlling an operation of the data storage device using the boosted voltage 14, and when the power voltage 12 falls below a threshold 16 at comparator 18, reducing the boosting 10 via control signal 20 so as to reduce the boosted voltage 14.

In the embodiment of FIG. 1A, the disk 4 comprises a plurality of servo tracks 22 defined by servo sectors 24₀-24_N, wherein data tracks are defined relative to the servo tracks at the same or different radial density. The control circuitry 8 processes a read signal 26 emanating from the head 2 to demodulate the servo sectors 24₀-24_N and generate a position error signal (PES) representing an error between the actual position of the head and a target position relative to a target track. The control circuitry 8 filters the PES using a suitable compensation filter to generate a control signal 28 applied to a voice coil motor (VCM) 30 which rotates an actuator arm 32 about a pivot in order to actuate the head 2 radially over the disk 4 in a direction that reduces the PES. The servo sectors 24₀-24_N may comprise any suitable head position information, such as a track address for coarse positioning and servo bursts for fine positioning. The servo bursts may comprise any suitable pattern, such as an amplitude based servo pattern or a phase based servo pattern.

FIG. 1B shows control circuitry according to an embodiment wherein during a power failure, the power voltage 12 generated based on the spindle motor 6 is applied to a VCM driver 34 which in one embodiment comprises field effect transistors (FETs) that form a H-bridge driver. The boosted voltage 14 is used to control an operation of the data storage device at block 36, such as finishing a current write command by flushing cached write data to a non-volatile semiconductor memory. In one embodiment, the power voltage 12 is generated based on a back electromotive force (BEMF) voltage generated by the spindle motor 6 using any suitable technique, such as the technique disclosed in U.S. Pat. No. 6,577,465 entitled “DISK DRIVE COMPRISING SPIN DOWN CIRCUITRY HAVING A PROGRAMMABLE SIGNAL GENERATOR FOR ENHANCING POWER AND BRAKING CONTROL” the disclosure of which is incorporated herein by reference.

In one embodiment, the magnitude of the input current to the voltage booster 10 depends on the magnitude of the power voltage 12, the boost factor K of the voltage booster 10, and the boost efficiency η, such that:
I_IN=I_OUT*K/η
The above equation illustrates that as the power voltage 12 decreases during a power failure (due to the kinetic energy of spindle motor decreasing as it slows), the amount of input current required to maintain the target boosted voltage 14 increases (due to the boost factor K increasing in the above equation). This is illustrated in the example of FIG. 2 wherein if the boosted voltage 12 were maintained at 5v as the power voltage 12 decreases to 0.8v, the boost factor K increases from 3.57 to 6.25 leading to a corresponding increase in current consumption by the voltage booster 10. As more current is consumed by the voltage booster 10, the power voltage 12 provides less current to the VCM driver 34 for parking the head 2 (e.g., unloading the head onto a ramp). This may result in less efficient power consumption by the control circuitry 10 and VCM driver 34, thereby decreasing performance and/or causing malfunction of the disk drive.

Accordingly, in one embodiment the power voltage 12 generated based on the spindle motor 6 is monitored during a power failure, and when the power voltage 12 falls below a threshold 16, the boosting of the power voltage 12 is reduced so as to reduce the boosted voltage (and corresponding boost factor K in the above equation). FIG. 2 shows an example of this embodiment wherein at the beginning of a power failure the voltage booster 10 is configured to generate a boosted voltage capped at 5v. When the power voltage 12 decreases to 5v, the boost factor K of the voltage booster 10 is unity. In one embodiment, when the power voltage 12 falls below 1.4v, the boosting by the voltage booster 10 is reduced so that:
V_BOOST=3*V_PWR+0.8
where V_PWR represents the power voltage 12 and V_BOOST represents the boosted voltage 14. In this manner, when the power voltage 12 decreases to 0.8v as in the above example, the boost factor K is reduced from 6.25 to 4.0, thereby providing more current to the VCM driver 34 to park the head 2. The above equation illustrates a particular embodiment whereas in general the boosted voltage 14 may be reduced based on:
V_BOOST=M*V_PWR

where M is a non-zero scalar. The above equation reduces the boosted voltage 14 based on a linear function of the power voltage 12, but other embodiments may employ any suitable function, such as any suitable polynomial. Other embodiments may reduce the boosted voltage 14 based on a non-linear function of the power voltage 12, such as by reducing the boosted voltage 14 in a step decrement as illustrated in the embodiment of FIG. 3, or by reducing the boosted voltage 14 by a staircase of decrements based on the power voltage 12 as illustrated in the embodiment of FIG. 4.

In one embodiment, as the boosted voltage 14 is reduced, the operation control 36 shown in FIG. 1B may be throttled in any suitable manner so that the power fail operation is more efficient in terms of power consumption and longevity. For example, in an embodiment where write data may be flushed to a non-volatile semiconductor memory during a power failure, the operating frequency of the control circuitry may be reduced so as to throttle down the flush operation to conserve power while ensuring the flush operation finishes before the power voltage 12 falls below a critical level. An example embodiment of this invention is disclosed in U.S. Pat. No. 8,630,054 entitled “SYSTEMS AND METHODS FOR DATA THROTTLING DURING DISK DRIVE POWER DOWN” the disclosure of which is incorporated herein by reference.

The voltage booster 10 shown in FIG. 1A may be implemented in any suitable manner, such as by using an inductive booster having a variable boost factor K. The power voltage 12 may also be monitored in any suitable manner during a power failure, such as by comparing the analog power voltage 12 to a threshold using an analog comparator, or by sampling the power voltage 12 and comparing the power voltage samples to a threshold using a digital comparator. Similarly, the boost factor K of the voltage booster 10 may be configured through analog control circuits and/or digital control circuits. For example, the voltage booster 10 may be programmably configured by a microprocessor executing the instructions of a control program.

While the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, solid state drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.

The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.

While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.