# Patent

## Title
Voice coil motor temperature sensing circuit to reduce catastrophic failure due to voice coil motor coil shorting to ground

## Abstract

An electrical circuit includes: a controlled switch; one or more temperature sensors in thermal contact with the controlled switch; and a control unit configured to: receive a temperature signal from the one or more temperature sensors; compare the received temperature signal to a predetermined threshold; and in response to the received temperature signal exceeding the predetermined threshold, render the controlled switch inoperative.

## Background
BACKGROUND
1. Technical Field
Apparatuses and methods consistent with the present inventive concept relate to current sensing, and more particularly to sensing overcurrent conditions in a voice coil motor circuit.
2. Related Art
During the lifetime of a data storage device there is a potential for metal debris resulting from internal component wear to come in contact with the coil of the voice coil motor (VCM). Over time this metal could damage the coil causing a short circuit to ground in the VCM drive circuitry. As a result, a large amount of current flowing to ground through the VCM drive circuitry and power supply circuitry can cause the affected printed circuit board assemblies to burn.
Conventionally, electronic fuses (E-fuses) may be used for over voltage and overcurrent protection. However, the response time of an E-fuse is insufficient to prevent damage caused by the rapid discharge of current built up in it in the inductance of the VCM coil resulting from a short circuit to ground.



BRIEF DESCRIPTION OF THE DRAWINGS
Aspects and features of the present inventive concept will be more apparent by describing example embodiments with reference to the accompanying drawings, in which:
FIG. 1 is a diagram illustrating current flow in a conventional H-bridge circuit;
FIG. 2A is a diagram illustrating an H-bridge circuit having temperature sensors according to various embodiments of the present inventive concept;
FIG. 2B is a diagram illustrating placement of temperature sensors relative to a controlled switch of an H-bridge circuit according to various embodiments of the present inventive concept;
FIG. 3 is a diagram illustrating an electrical circuit according to various embodiments of the present inventive concept;
FIG. 4 is a diagram illustrating an electrical circuit in a data storage device according to various embodiments of the present inventive concept;
FIG. 5 is a flow chart illustrating a method according to various embodiments of the present inventive concept; and
FIG. 6 is a flow chart illustrating a method according to various embodiments of the present inventive concept.



DETAILED DESCRIPTION
While certain embodiments are described, these embodiments are presented by way of example only, and are not intended to limit the scope of protection. The 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 example methods and systems described herein may be made without departing from the scope of protection.
Overview
The drive circuit for a VCM provides high current to permit the VCM to rapidly move a read-write head actuator arm across a recording medium. A conventional drive circuit for a VCM may be configured as an H-bridge circuit. FIG. 1 is a diagram illustrating current flow in a conventional H-bridge circuit.
Referring to FIG. 1, the conventional H-bridge circuit 110 may include a first controlled switch 114a, a second controlled switch 114b, a third controlled switch 114c, a fourth controlled switch 114d, and a VCM 120. The controlled switches may be, for example, but not limited to, field-effect transistors (FETs) or other circuit elements or semiconductor or mechanical/electromechanical switches. One of ordinary skill in the art will appreciate that each of the controlled switches may include more than one switching device or circuit element without departing from the scope of the present inventive concept.
To move the read-write head actuator arm in a first direction, the first controlled switch 114a and the second controlled switch 114b may be activated while the third controlled switch 114c and the fourth controlled switch 114d remain inactive permitting current to flow in a first direction 140 through the first controlled switch 114a, the VCM 120, and the second controlled switch 114b causing the read-write head actuator arm 420 (refer to FIG. 4) to move in the first direction. To move the read-write head actuator arm in a second (opposite) direction, the first controlled switch 114a and the second controlled switch 114b may be deactivated while the third controlled switch 114c and the fourth controlled switch 114d are activated permitting current to flow in a second direction 150 through the third controlled switch 114c, the VCM 120, and the fourth controlled switch 114d causing the read-write head actuator arm 420 (refer to FIG. 4) to move in the second direction. The current flow through the VCM 120 stores energy in a magnetic field in the inductance of the VCM 120.
If the VCM 120 coil becomes damaged causing a short circuit to ground a large current may flow through one or more of the controlled switches 114a-114d from the power supply 130 and/or the energy stored in the magnetic field in the inductance of the VCM 120. An increase in current flowing through any of the controlled switches 114a-114d may cause a rise in operating temperature of the controlled switches 114a-114d having the increased current flow. Therefore, the increased current flow may be sensed based on sensing a rise in operating temperature of the controlled switches 114a-114d. 
Current Sensing Based on Temperature
FIG. 2A is a diagram illustrating an H-bridge circuit 210 having temperature sensors according to various embodiments of the present inventive concept. Referring to FIG. 2A, at least two temperature sensors 220-290 may be provided for each controlled switch 114a-114d. The temperature sensors 220-290 may be, for example, but not limited to, diode temperature sensors or other semiconductor junction devices. Operating temperatures of the controlled switches 114a-114d may be sensed by the temperature sensors 220-290 and converted to electrical signals representing the temperatures.
FIG. 2B is a diagram illustrating placement of temperature sensors relative to a controlled switch of an H-bridge circuit according to various embodiments of the present inventive concept. Referring to FIG. 2B, the temperature sensors 220, 230 may be integrated on a semiconductor die 215 in conjunction with formation of a controlled switch 214a thereby ensuring that the temperature sensors 220, 230 are in thermal contact with the controlled switch 214a. In some embodiments, the temperature sensors 220, 230 may be formed on the semiconductor die 215 at opposite corners of the controlled switch 214a structure. In some embodiments, the controlled switch 214a may be, for example, but not limited to, an FET, and the temperature sensors 220, 230 may be formed on the semiconductor die 215 at opposite corners of the FET structure.
FIG. 3 is a diagram illustrating an electrical circuit 310 according to various embodiments of the present inventive concept. Referring to FIGS. 2A and 3, the electrical circuit 310 may include an H-bridge circuit 210, drive circuitry 360 for the H-bridge circuit 210, a control unit 370, and a memory 380. The memory 380 may be nonvolatile memory, for example, but not limited to, EPROM memory, EEPROM memory, etc. The H-bridge circuit 210 may include a plurality of controlled switches 214a-214d and a plurality of temperature sensors 220-290.
The drive circuitry 360 may be electrically connected to a control terminal 330 of each of the plurality of controlled switches 214a-214d. The control unit 370 may control the drive circuitry 360 to cause the drive circuitry 360 to activate and deactivate the controlled switches 214a-214d as required to cause the VCM 120 to move the read-write head actuator arm 420 (refer to FIG. 4).
At least two temperature sensors 200-290 may be provided for each of the controlled switches 214a-214d. Referring to FIG. 3, one representative controlled switch 214a and two representative temperature sensors 220, 230 are illustrated. The temperature sensors 200, 230 may be in thermal contact with the controlled switch 214a to sense the operating temperature of the controlled switch 214a. 
In some embodiments, a diode temperature sensor 220, 230 may be provided with current from a current source 340, 350. With a constant current applied, the voltage across the diode temperature sensor 220, 230 will decrease by approximately 1 to 2 mV/° C. over temperature. The voltage change over temperature may be used with a look up table or an equation to calculate a temperature.
In some embodiments, operating temperatures of the controlled switches 214a-214d of the H-bridge circuit 210 may be characterized over different operating conditions for the VCM 120 and temperature profiles stored in the memory 380. An absolute maximum operating temperature for the controlled switches 214a-214d may also be stored in the memory 380.
Referring again to FIG. 3, the control unit 370 may receive electrical signals 372, 374 representing the operating temperature (i.e., temperature signals) of the controlled switch 214a from the temperature sensors 220, 230. The control unit 370 may compare the operating temperature indicated by each of the temperature signals 372, 374 from the temperature sensors 220, 230 to a predetermined threshold, for example, the absolute maximum operating temperature stored in the memory 380.
If any of the temperature signals 372, 374 exceeds the predetermined threshold, the increased temperature may indicate an overcurrent condition in the H-bridge circuit 210, for example, due to a short circuit to ground in the VCM 120 coil. In response, the control unit 370 may record the increased temperature as an over-temperature event in a designated field of a Drive Reliability Management (DRM) log on the storage medium 430 (refer to FIG. 4). The control unit 370 may then render all of the controlled switches 214a-214d inoperative by causing the drive circuitry 360 to command the controlled switches 214a-214d to a state that prevents electrical current flow through the controlled terminals (e.g., the drain and source terminals on an FET) of the controlled switches 214a-214d. For example, the drive circuitry 360 may provide a signal to the control terminal 330 of the controlled switch 214a to deactivate the controlled switch 214a, or the controlled switch 214a may otherwise be commanded to a high impedance state. Information recorded in the DRM log may subsequently be accessed from the storage medium 430 of a failed data storage device 410 (refer to FIG. 4).
Alternatively or additionally, the control unit 370 may compare the operating temperature of each controlled switch 214a-214d to the operating temperature of every other controlled switch 214a-214d. The control unit 370 may determine an operating temperature for the controlled switch 214a from the temperature signals 372, 374 received from the temperature sensors 220, 230 of the controlled switch 214a. For example, the control unit 370 may average the temperature signals 372, 374 received from the temperature sensors 220, 230 of the controlled switch 214a to generate an operating temperature for the controlled switch 214a. The control unit 370 may compare the operating temperature of the controlled switch 214a to similarly determined operating temperatures of each of the other controlled switches 214b-214d in the H-bridge circuit 210.
If the control unit 370 determines that the operating temperature of the controlled switch 214a is greater than a predetermined amount, for example about 5-10° C., compared to the operating temperature of any other of the controlled switches 214b-214d, an overcurrent condition, for example, a short circuit to ground in the VCM 120 coil, may be indicated. In response, the control unit 370 may record the increased temperature as an over-temperature event in a designated field of a Drive Reliability Management (DRM) log on the storage medium 430 (refer to FIG. 4). The control unit 370 may then render all of the controlled switches 214a-214d inoperative. Information recorded in the DRM log may subsequently be accessed from the storage medium 430 of a failed data storage device 410 (refer to FIG. 4).
The predetermined amount of temperature difference between the operating temperatures of the controlled switches 214a-214d may vary based on the temperature profiles of the controlled switches 214a-214d characterized over different operating conditions stored in the memory 380.
One of ordinary skill in the art will appreciate that other methods of determining the operating temperatures of the controlled switches and comparing operating temperatures of the controlled switches with each other may be performed without departing from the scope of the present inventive concept.
Although operation of the electrical circuit 310 has been described with respect to one controlled switch 214a and associated temperature sensors 220, 230 of the H-bridge circuit 210, one of ordinary skill in the art will appreciate that operation of the electrical circuit 310 extends to each controlled switch 214a-214d and associated temperature sensors 220-290.
FIG. 4 is a diagram illustrating an electrical circuit 310 in a data storage device (DSD) 410 according to various embodiments of the present inventive concept. Referring to FIG. 4, the electrical circuit 310 in the DSD 410 may control the VCM 120 to move the read-write head actuator arm 420 across a storage medium 430.
When an overcurrent condition is detected in the H-bridge circuit 210, the control unit 370 may cause the electrical circuit 310 to initiate one or more predetermined operations prior to rendering the controlled switches 214a-214d inoperative. For example, the control unit 370 may cause the electrical circuit 310 to initiate an emergency power-off retract (EPOR) of the read-write head actuator arm 420 from the storage medium 430. One of ordinary skill in the art will appreciate that other operations may be initiated prior to rendering the controlled switches 214a-214d inoperative without departing from the scope of the present inventive concept.
FIG. 5 is a flow chart illustrating a method 500 according to various embodiments of the present inventive concept. Referring to FIGS. 2A, 3, and 5, the control unit 370 may monitor the temperature of one or more circuit elements (e.g., the controlled switches 114a-114d) sensed by temperature sensors (e.g., the diode temperature sensors 220-290) (510). Each of the circuit elements may be provided with at least two temperature sensors.
The control unit 370 may compare the temperature sensed by each of the temperature sensors to a predetermined threshold (520). The predetermined threshold may correspond to an absolute maximum temperature rating of the circuit elements being monitored and may be stored in the memory 380. If the control unit 370 determines that none of the monitored circuit element temperatures exceeds the predetermined threshold (530—N), the control unit 370 may continue to monitor the temperature of the one or more circuit elements (510).
If the control unit 370 determines that at least one of the monitored circuit element temperatures exceeds the predetermined threshold (530—Y), the control unit 370 may record an over-temperature event in a designated field of the DRM log (540). The control unit 370 may then render the circuit elements inoperative (550).
The control unit 370 may render all of the circuit elements 214a-214d inoperative by commanding the circuit elements 214a-214d to a state that prevents electrical current flow through the circuit elements 214a-214d. For example, the control unit 370 may provide a signal to deactivate the circuit elements 214a-214d, or the circuit elements 214a-214d may otherwise be commanded to a high impedance state.
FIG. 6 is a flow chart illustrating a method 600 according to various embodiments of the present inventive concept. Referring to FIGS. 2A, 3, and 6, the control unit 370 may monitor the temperature of one or more controlled switches 114a-114d of the H-bridge circuit 210 sensed by temperature sensors (e.g., the diode temperature sensors 220-290) (610). The controlled switches 114a-114d may be for example, but not limited to, FETs or other circuit elements, semiconductor or mechanical/electromechanical switches. Each of the controlled switches 114a-114d may be provided with at least two temperature sensors 220-290.
The control unit 370 may determine an operating temperature for the controlled switch 214a from the temperature signals 372, 374 received from the temperature sensors 220, 230 of the controlled switch 214a (615). For example, the control unit 370 may average the temperature signals 372, 374 received from the temperature sensors 220, 230 of the controlled switch 214a to generate an operating temperature for the controlled switch 214a. 
The control unit 370 may compare the operating temperature of the controlled switch 214a to similarly determined operating temperatures of each of the other controlled switches 214b-214d in the H-bridge circuit 210 (620). If the control unit 370 determines that the operating temperature of the controlled switch 214a is greater than a predetermined amount for example about 5-10° C., compared to the operating temperature of any other of the controlled switches 214b-214d (625—Y), an overcurrent condition, for example, a short circuit to ground in the VCM 120 coil, may be indicated.
In response to the detected overcurrent condition, the control unit 370 may record an over-temperature event in a designated field of the DRM log (640). The control unit 370 may cause the electrical circuit 310 to initiate one or more predetermined operations (645). For example, the control unit 370 may cause the electrical circuit 310 to initiate an emergency power-off retract (EPOR) of the read-write head actuator arm 420. The control unit 370 may then render all of the controlled switches 214a-214d inoperative (650).
If the control unit 370 determines that the operating temperature of the controlled switch 214a is not greater than a predetermined amount compared to the operating temperature of any other of the controlled switches 214b-214d (625—N), the control unit 370 may compare the operating temperatures of each of the controlled switches 214a-214d or the temperature signals from each of the temperature sensors 220-290 to a predetermined threshold (630). The predetermined threshold may correspond to an absolute maximum temperature rating of the circuit elements (e.g., controlled switches 214a-214d) being monitored and may be stored in the memory 380.
If the operating temperatures of any of the controlled switches 214a-214d or a temperature signal from any of the temperature sensors 220-290 does not exceed the predetermined threshold (635—N), the control unit 370 may continue to monitor the temperature of one or more controlled switches 114a-114d (610). If the operating temperatures of any of the controlled switches 214a-214d or a temperature signal from any of the temperature sensors 220-290 exceeds the predetermined threshold (635—Y), an overcurrent condition, for example, a short circuit to ground in the VCM 120 coil, may be indicated.
In response to the detected overcurrent condition, the control unit 370 may record an over-temperature event in a designated field of the DRM log (640). The control unit 370 may cause the electrical circuit 310 to initiate one or more predetermined operations (645). For example, the control unit 370 may cause the electrical circuit 310 to initiate an emergency power-off retract (EPOR) of the read-write head actuator arm 420. The control unit 370 may then render all of the controlled switches 214a-214d inoperative (650).
The control unit 370 may render all of the controlled switches 214a-214d inoperative by causing the drive circuitry 360 to command the controlled switches 214a-214d to a state that prevents electrical current flow through the controlled terminals of the controlled switches 214a-214d. For example, the drive circuitry 360 may provide a signal to the control terminal 330 of the controlled switch 214a to deactivate the controlled switch 214a, or the controlled switch 214a may otherwise be commanded to a high impedance state.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the protection. The methods and systems described herein may be embodied in a variety of other forms. Various omissions, substitutions, and/or changes in the form of the example methods and systems described herein may be made without departing from the spirit of the protection.
The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the protection. For example, the example systems and methods disclosed herein can be applied to hard disk drives, hybrid hard drives, and the like. In addition, other forms of storage, for example, but not limited to, DRAM or SRAM, battery backed-up volatile DRAM or SRAM devices, EPROM, EEPROM memory, etc., may additionally or alternatively be used. As another example, the various components illustrated in the figures may be implemented as software and/or firmware on a processor, ASIC/FPGA, or dedicated hardware. Also, the features and attributes of the specific example embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure.
Although the present disclosure provides certain example embodiments and applications, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by reference to the appended claims.

## Claims

1. An electrical circuit, comprising:
a plurality of controlled switches, each of the plurality of controlled switches having one or more temperature sensors in thermal contact with each of the plurality of controlled switches, and
a control unit configured to:
receive temperature signals from the one or more temperature sensors;
compare the received temperature signals of each of the plurality of controlled switches to the received temperature signals of every other one of the plurality of controlled switches;
in response to a variation in the received temperature signals of any of the plurality of controlled switches greater than a predetermined amount compared to the received temperature signals of any other one of the plurality of controlled switches, render the plurality of controlled switches inoperative; and
in response to the variation in the received temperature signal exceeding the predetermined amount, record an over-temperature event.

2. The electrical circuit of claim 1, wherein the predetermined amount of variation in the received temperature signals is variable based on operating conditions of the electrical circuit.

3. The electrical circuit of claim 1, wherein the control unit is further configured to cause the electrical circuit to initiate one or more predetermined operations prior to rendering the controlled switch inoperative.

4. The electrical circuit of claim 1, wherein the temperature sensors are diode temperature sensors.

5. The electrical circuit of claim 4, wherein the diode temperature sensors are formed on a semiconductor die at opposite corners of a controlled switch structure formed on the semiconductor die.

6. The electrical circuit of claim 1, wherein the control unit is further configured to render the plurality of controlled switches inoperative by commanding the plurality of controlled switches a to a high impedance state.

7. The electrical circuit of claim 1, wherein the rendering the plurality of controlled switches inoperative comprises configuring the plurality of controlled switches so as not to permit electrical current flow through controlled terminals of the plurality of controlled switches.

8. The electrical circuit of claim 1, wherein the controlled switches are field effect transistors (FETs).

9. An electrical circuit, comprising:
a plurality of field effect transistors (FETs) configured as an H-bridge circuit;
one or more temperature sensors integrated with each of the plurality of FETs; and
a control unit configured to:
receive temperature signals from the one or more temperature sensors;
compare the received temperature signals from the one or more temperature sensors of each of the plurality of FETs to the received temperature signals from the one or more temperature sensors of every other one of the plurality of FETs;
in response to a variation in the received temperature signals from the one or more temperature sensors of any one of the plurality of FETs greater than a predetermined amount compared to the received temperature signals from the one or more temperature sensors of any other one of the plurality of FETs, render the plurality of FETs inoperative; and
in response to the variation in the received temperature signals exceeding the predetermined amount, record an over-temperature event.

10. The electrical circuit of claim 9, wherein the predetermined amount of variation in the received temperature signals is variable based on operating conditions of the electrical circuit.

11. The electrical circuit of claim 9, wherein the control unit is further configured to cause the electrical circuit to initiate one or more predetermined operations prior to rendering the plurality of FETs inoperative.

12. The electrical circuit of claim 9, wherein the one or more temperature sensors are diode temperature sensors.

13. The electrical circuit of claim 12, wherein the diode temperature sensors are formed on a semiconductor die at opposite corners of a FET structure formed on the semiconductor die.

14. The electrical circuit of claim 9, wherein the rendering the plurality of FETs inoperative comprises commanding the plurality of FETs to a high impedance state.

15. The electrical circuit of claim 9, wherein the rendering the plurality FETs inoperative comprises preventing current flow from a drain terminal to a source terminal of each of the plurality of FETs.

16. A method for sensing an overcurrent condition in an electrical circuit, the method comprising:
monitoring temperature of one or more circuit elements;
comparing the monitored temperature of each of the one or more circuit elements to the monitored temperature of every other one of the one or more circuit elements;
in response to a variation in the monitored temperature of any of the one or more circuit elements greater than a predetermined amount compared to the monitored temperature of any other one of the one or more circuit elements, rendering the one or more circuit elements inoperative, and
in response to the variation in the monitored temperature of any of the one or more circuit elements exceeding the predetermined amount, recording an over-temperature event.

17. The method of claim 16, wherein the predetermined amount of variation in the monitored temperature is variable based on operating conditions of the electrical circuit.

18. The method of claim 16, further comprising, prior to rendering the one or more circuit elements inoperative, causing the electrical circuit to initiate one or more predetermined operations.

19. The method of claim 16, wherein the rendering the one or more circuit elements inoperative comprises configuring the electrical circuit so as not to permit electrical current flow through the one or more circuit elements.

20. A data storage device (DSD), comprising:
an electrical circuit, comprising:
a plurality of field effect transistors (FETs) configured as an H-bridge circuit;
one or more temperature sensors integrated with each of the plurality of FETs; and
a control unit configured to:
receive temperature signals from the one or more temperature sensors;
compare the received temperature signals from the one or more temperature sensors of each of the plurality of FETs to received temperature signals from the one or more temperature sensors of every other one of the plurality of FETs;
in response to a variation in the received temperature signals from the one or more temperature sensors of any one of the plurality of FETs greater than a predetermined amount compared to the received temperature signals from the one or more temperature sensors of any other one of the plurality of FETs, render the plurality of FETs inoperative; and
in response to the variation in the received temperature signals exceeding the predetermined amount, record an over-temperature event.

21. The DSD of claim 20, wherein the predetermined amount of variation in the received temperature signals is variable based on operating conditions of the electrical circuit.

22. The DSD of claim 20, wherein the control unit is further configured to cause the electrical circuit to initiate one or more predetermined operations prior to rendering the plurality of FETs inoperative.

23. The DSD of claim 22, wherein at least one of the predetermined operations is an emergency power-off retract of a read-write head actuator arm.

24. The DSD of claim 20, wherein the one or more temperature sensors are diode temperature sensors.

25. The DSD of claim 24, wherein the diode temperature sensors are formed on a semiconductor die at opposite corners of a FET structure formed on the semiconductor die.

26. The DSD of claim 20, wherein the rendering the plurality of FETs inoperative comprises commanding the plurality of FETs to a high impedance state.

27. The DSD of claim 20, wherein the rendering the plurality FETs inoperative comprises preventing current flow from a drain terminal to a source terminal of each of the plurality of FETs.