Extending and scavenging super-capacitor capacity

• US 8,161,310 B2
• Filed: 04/08/2008
• Issued: 04/17/2012
• Est. Priority Date: 04/08/2008
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: International Business Machines Corporation
• Inventors: Cagno, Brian J., Elliott, John C., Lucas, Gregg S., Kubo, Robert A.
• Primary Examiner(s): Lee, Chun-Kuan
• Assistant Examiner(s): Yimer, Getente A
• Application Number:
  US12/099,373
• Publication Number:
  US 20090254772A1
• Time in Patent Office: 1,470 Days
• Field of Search: 713/324
• US Class Current: 713/340
• CPC Class Codes: G06F 1/28 Supervision thereof, e.g. detecting power-supply failure by out of limits supervision
• CPC Class Codes: G11C 11/4074 Power supply or voltage generation circuits, e.g. bias voltage generators, substrate voltage generators, back-up power, power control circuits
• CPC Class Codes: G11C 5/141 Battery and back-up supplies

Abstract

A memory system has mechanisms for scavenging capacity of a super capacitor by removing, or reducing, system load from the super capacitor when the super capacitor voltage decays below a low threshold. The mechanisms then restore the system load to the super capacitor when the super capacitor voltage ramps back above a high threshold. A controller may reduce system load by placing a volatile memory system in a standby state and disabling a field effect transistor to remove power from a non-volatile memory system. A controller may adjust the high threshold and/or a low threshold by setting a digitally controlled potentiometer in a threshold detect circuit via an I²C bus.

Claims

1. A computer program product comprising a computer storage medium having a computer readable program stored thereon, wherein the computer readable program, when executed on a computing device, causes the computing device to:

initializing a low threshold and a high threshold;

responsive to an early power off warning, transition to backup mode and enable a super capacitor to provide power;

reducing system load on the super capacitor responsive to a voltage level of the super capacitor dropping below the low threshold;

restore the system load on the super capacitor and continue operation of the backup mode responsive to the voltage level of the super capacitor ramping up to the higher threshold;

reducing the system load on the super capacitor responsive to the voltage level of the super capacitor dropping below the low threshold subsequent to the previous restoring of the system load;

decrease the high threshold in response to repeating the reducing of the system load;

determine whether the high threshold is within a predetermined range of the low threshold; and

stop operation of the backup mode responsive to the high threshold being within the predetermined range of the low threshold.

2. The computer program product of claim 1, wherein he computer readable program further causes the computing device to

repeat restoring the system load on the super capacitor and continuing operation of the backup mode responsive to the voltage level of the super capacitor ramping up to the high threshold, reducing system load on the super capacitor responsive to the voltage level of the super capacitor dropping below the low threshold, and adjusting the high threshold until the high threshold is within a predetermined range of the low threshold.

3. The computer program product of claim 2, wherein the backup mode comprises a memory backup mode to store data from a volatile memory to a non-volatile memory using power provided by the super capacitor responsive to the early power off warning, and wherein reducing system load on the super capacitor comprises placing the volatile memory in a standby state.

4. The computer program product of claim 3, wherein restoring the system load on the super capacitor comprises placing the volatile memory in a non-standby state.

5. The computer program product of claim 2, wherein the backup mode comprises a memory backup mode to store data frorn a volatile memory to a non-volatile memory using power provided by the super capacitor responsive to the early power off warning, and wherein reducing system load on the super capacitor comprises disabling power to the non-volatile memory.

6. The computer program product of claim 5, wherein restoring the system load on the super capacitor comprises enabling power to the non-volatile memory.

7. A method, in a data processing system, for scavenging super capacitor capacity, the method comprising:

Initializing a low threshold and a high threshold;

responsive to an early power off warning, transition to backup mode and enabling a super capacitor to provide power;

responsive to a voltage level of the super capacitor dropping below the low threshold, reducing the system load on the super capacitor;

responsive to the voltage level of the super capacitor ramping up to a high threshold, restore the system load on the super capacitor and continuing operation of the backup mode;

reducing the system load on the super capacitor responsive to the voltage level of the super capacitor dropping below the low threshold subsequent to the previous restoring of the system load;

decrease the high threshold in response to repeating the reducing of the system load;

determining whether the high threshold is within a predetermined range of the low threshold; and

stopping operation of the backup mode responsive to the high threshold being within the predetermined range of the low threshold.

8. The method of claim 7, further comprising:

repeat restoring the system load on the super capacitor and continuing operation of the backup mode responsive to the voltage level of the super capacitor ramping up to the high threshold, reducing system load on the super capacitor responsive to the voltage level of the super capacitor dropping below the low threshold, and adjusting the high threshold until the high threshold is within a predetermined range of the low threshold.

9. The method of claim 7, wherein the backup mode comprises memory backup mode to store data from a volatile memory to a lion-volatile memory using power provided by the super capacitor responsive to the early power off warning, and wherein reducing system load on the super capacitor comprises placing the volatile memory in a standby state.

10. The method of claim 9, wherein restoring the system load on the super capacitor comprises placing, the volatile memory in a non-standby state.

11. The method of claim 7, wherein the backup mode comprises a memory backup mode to store data from a volatile memory to a non-volatile memory using power provided by the super capacitor responsive to the early power off warning, and wherein reducing system load on the super capacitor comprises disabling power to the non-volatile memory.

12. The method of claim 11, wherein restoring the system load on the super capacitor comprises enabling power to the non-volatile memory.

13. A memory system comprising:

a controller, wherein the controller is configure to detect a power event from a power supply the provides power to a storage controller and the memory system;

a volatile memory;

a non-volatile memory; and

a super capacitor, wherein the super capacitor is configured to provide power to the memory system response to the power event,

wherein the controller is configured to transition to memory backup mode to store data from the volatile memory to the non-volatile memory using power provided by the super capacitor responsive to the power event, reduce the system load on the super capacitor responsive to a voltage level of the super capacitor dropping below a low threshold, restore the system load on the super capacitor and continuing operation of the backup mode responsive to the voltage level of the super capacitor ramping up to a high threshold, reduce the system load on the super capacitor responsive to the voltage level of the super capacitor dropping below the low threshold subsequent to the previous restoring of the system load, decrease the high threshold in response to repeating the reducing of the system load, determine whether the high threshold is within a predetermined range of the low threshold, and stop operation of the backup mode responsive to the high threshold being within the predetermined range of the low threshold.

14. The memory system of claim 13, further comprising:

a low threshold detect circuit that generates a low threshold detect signal responsive to the voltage level of the hold-up voltage source dropping below a low threshold; and

a high threshold detect circuit that generates a high threshold detect signal responsive to the voltage level of the hold-up voltage source ramping up to the high threshold.

15. The memory system of claim 14, wherein the low threshold detect comprises:

a comparator that compares a first reference voltage to a second reference voltage, wherein the first reference voltage is derived from the voltage level of the hold-up voltage source and wherein the second reference voltage is derived from a Zener voltage of a Zener diode.

16. The memory system of claim 14, wherein the high threshold detect circuit comprises:

a comparator that compares a first reference voltage to a second reference voltage, wherein the first reference voltage is derived from the voltage level of the hold-up voltage source and wherein the second reference voltage is derived from a Zener voltage of a Zener diode using a voltage divider.

17. The memory system of claim 16, wherein the voltage divider comprises a digitally controlled potentiometer and wherein the controller sets the high threshold by setting the digitally controlled potentiometer.

18. The memory system of claim 13, wherein the controller is configured to:

repeat restoring the system load on the super capacitor and continuing operation of the backup mode responsive to the voltage level of the super capacitor ramping up to the high threshold, reducing system load on the super capacitor responsive to the voltage level of he super capacitor dropping below the low threshold, and adjusting the high threshold until the high threshold is within a predetermined range of the low threshold.