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An embodiment of a circuit for maintaining voltage at a voltage bus after a power loss in a hard disk drive system. HDD systems may suddenly lose power and specific tasks, such as parking the read/write head and storing state data may be accomplished using a power generated from back EMF of a motor

An embodiment of a circuit for maintaining voltage at a voltage bus after a power loss in a hard disk drive system. HDD systems may suddenly lose power and specific tasks, such as parking the read/write head and storing state data may be accomplished using a power generated from back EMF of a motor that is still turning. During the power loss sequence, a drive controller may drive a power chipset to regulate the voltage at a voltage bus so as to conserve power as much as possible. In this manner, the drive circuit may regulate the voltage via a drive algorithm to be just above a threshold voltage (typically 4.4 V) while the HDD system is storing state data, but apply other algorithm for other situations, such as parking the read/write head. Various drive algorithms may be tailored to provide a specific sequence of voltage bus regulation techniques suited to specific applications.

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1. A circuit, comprising: a driver configured to be coupled to a rotating motor and configured to receive at least one phase voltage from the rotating motor and to generate a voltage on a supply node by coupling the phase voltage to the supply node in response to a pulse-width modulated signal;a vol

1. A circuit, comprising: a driver configured to be coupled to a rotating motor and configured to receive at least one phase voltage from the rotating motor and to generate a voltage on a supply node by coupling the phase voltage to the supply node in response to a pulse-width modulated signal;a voltage comparator configured to compare the voltage at the supply node to a threshold voltage; anda controller configured to generate the pulse-width modulated signal to adjust a switching characteristic of the driver based upon the comparison by the voltage comparator, the generated pulse-width modulated signal having a characteristic to change power delivered to the supply node. 2. The circuit of claim 1 wherein the circuit is disposed in a hard disk drive system. 3. The circuit of claim 1 wherein the threshold voltage comprises approximately 4.4 volts. 4. The circuit of claim 1 wherein the driver further comprises three pairs of MOSFET transistors, each pair configured to generate a voltage corresponding to one of three phase voltages of the motor. 5. The circuit of claim 1 wherein controller is further configured to: adjust the pulse-width modulated signal to have a higher modulation if the voltage at the supply node is above the threshold voltage; andadjust the pulse-width modulated signal to have a lower modulation if the voltage at the supply node is below the threshold voltage. 6. The circuit of claim 1 wherein the controller is further configured to: generate a first pulse-width modulated signal having a first switching characteristic during a first drive phase; andgenerate a second pulse-width modulated signal having a second switching characteristic during a second drive phase. 7. The circuit of claim 6 wherein the controller is further configured to: generate a parking control signal during the first phase; andgenerate a read/write instruction during the second phase. 8. The circuit of claim 1 further comprising an integrated circuit disposed on a single die. 9. A system, comprising: a motor configured to generate a back electromotive force at a first terminal;a load unrelated to the motor electrically coupled to the first terminal;a voltage comparator configured to compare the voltage at the first terminal to a threshold voltage; anda control circuit coupled to the motor configured to maintain power at the first terminal by switching the electrical coupling according to one of a plurality of power-loss switching algorithms. 10. The system of claim 9 wherein the control circuit comprises: a driver configured to switch the electrical coupling between the load and the first terminal; anda controller configured to adjust the switching based upon the comparison by the voltage comparator. 11. The system of claim 9, further comprising a flash memory for storing state information after a power loss. 12. The system of claim 9, further comprising: a hard disk coupled to a read/write channel; anda processor configured to control operations of the read/write channel and coupled to the control circuit such that the control circuit is controlled by the processor. 13. A method for maintaining a voltage level at a node during power loss, the method comprising: determining a voltage at a node when a power loss is detected, the voltage generated by a back electromotive force from a motor;comparing the voltage level to a threshold voltage; andregulating the voltage according to a pulse-width modulated drive algorithm to maintain power delivered to a load in response to the comparison, such that the drive algorithm that maximizes power delivered to a load coupled to the node, wherein the load is a load other than the motor. 14. The method of claim 13, further comprising regulating the voltage according to a drive algorithm that delivers a first level of power during a first phase and a second level of power during a second phase. 15. The method of claim 14, further comprising: causing the parking of a read/write head during the first phase; andcausing the performing of write operations to a flash memory during the second phase. 16. The method of claim 13, further comprising regulating the voltage according to a drive algorithm that maintains power delivered to a load coupled to the node at a threshold that comprises a voltage buffer above the threshold voltage, wherein the load is a load other than the motor. 17. The method of claim 13, further comprising: if the compared voltage is above the voltage threshold, then incrementing the regulation toward a maximum efficiency drive algorithm; andif the compared voltage is below the voltage threshold, then incrementing the regulation toward a maximum power drive algorithm. 18. The method of claim 13, further comprising: detecting a power spike at the voltage bus; andin response, adjusting the drive algorithm to provide more power to the voltage bus. 19. The method of claim 13, further comprising: detecting an excess voltage at the voltage bus; andin response, adjusting the drive algorithm to provide less power to the voltage bus. 20. A circuit, comprising: a driver configured to be coupled to a rotating motor and configured to receive at least one phase voltage from the rotating motor and to generate a voltage on a supply node by coupling the phase voltage to the supply node in response to a pulse-width modulated signal;a voltage comparator configured to compare the voltage at the supply node to a threshold voltage; anda controller configured to generate the pulse-width modulated signal to adjust a switching characteristic of the driver based upon the comparison by the voltage comparator, the generated pulse-width modulated signal having a characteristic to affect power efficiency delivered to the supply node.