Method for monitoring end of life for battery

• US 20020140404A1
• Filed: 03/06/2002
• Published: 10/03/2002
• Est. Priority Date: 09/15/1997
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Lyden, Michael J.
• Granted Patent: US 6,654,640 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: A61N 1/3708 for power depletion
• CPC Class Codes: A61N 1/378 Electrical supply
• CPC Class Codes: G01R 31/3647 for determining the ability of a battery to perform a critical function, e.g. cranking
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: H02J 2310/23 The load being a medical device, a medical implant, or a life supporting device
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]

Abstract

A system is described. The system includes a lithium battery, a charge storage capacitor electrically connected to the lithium battery, a first device, and at least one second device. The first device is electrically connected to the lithium battery and is powered by the lithium battery. The at least one second device is attached to the charge storage capacitor and adapted to read a rate of charge storage in the charge storage capacitor or to calculate the rate of charge storage by measuring both a time of charging and a charge stored or added to the charge storage capacitor during the time of charging.

Claims

1. A system having a lithium battery, a device which is powered by said lithium batter in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

c) reading the rate of charge storage or

d) measuring both time and charge stored or added to said charge storage capacitor so that a rate of charge storage may be calculated.

2. A cardiac pacing system having a lithium battery, a device which delivers electric current to a patient, which device is powered by said lithium battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

a) reading the rate of charge storage or

b) measuring both time and charge stored or added to said charge storage capacitor so that a rate of charge storage may be calculated.

3. The pacing system of claim 2 wherein said storage capacitor is a storage capacitor from which stored energy is used to apply a pace to a patient.

4. The pacing system of claim 2 wherein said storage capacitor is substantially uninvolved in application of a pace to a patient and is present to provide a basis of measuring capacitor charge rate during a relatively quiescent period within a period of episodic power utilization by said device.

5. A process for estimating a level of power depletion in a system having a lithium battery, a cardiac pacing device which is powered by said lithium battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

a) reading the rate of charge storage or

b) measuring both time and charge stored or added to said charge storage capacitor so that a rate of charge storage may be calculated,

said process comprising

i) finding a relatively quiescent period in powering of said device in said episodic manner,

ii) determining a rate of charging in said storage capacitor during said quiescent period,

iii) correlating said rate of charging in said storage capacitor to a value of internal resistance in said battery through a comparison with known relationships for said battery and rate of charging to determine a value for the internal impedance of said battery.

6. The process of claim 5 wherein said comparison is done by use of a look-up table having predetermined quantitative comparisons of measured capacitor charge rates and Internal Impedance for a particular battery.

7. The process of claim 5 wherein after determining a value for the Internal Impedance of said battery, said value for Internal AC Impedance of said battery is used to determine a value for expended energy from said battery.

8. The process of claim 7 wherein the use of said value for Internal AC Impedance of said battery to determine a value for expended energy is effected by reference to a graphic representation of a relationship between Internal AC Impedance of said battery and energy expended from said battery.

9. The process of claim 5 wherein said storage capacitor is used to store energy which is used to energize a pace from said pacing system to a patient.

10. The process of claim 5 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

11. The process of claim 5 wherein said quiescent period immediately follows a ventricular pace or pulse.

12. The process of claim 7 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

13. The process of claim 8 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

14. The process of claim 7 wherein said quiescent period immediately follows a ventricular pace or pulse.

15. The process of claim 8 wherein said quiescent period immediately follows a ventricular pace or pulse.

18. The process of claim 5 wherein said charge rate is determined over a time period beginning when the capacitor is not fully discharged and has a predetermined minimum charge differential across the capacitor so that upon initiation of an episodic charging event, the storage capacitor is discharged to at least said predetermined minimum.

19. The process of claim 12 wherein said charge rate is determined over a time period beginning when the capacitor is not fully discharged and has a minimum charge differential across the capacitor so that upon initiation of an episodic charging event, the storage capacitor is discharged to at least said predetermined minimum.

20. The process of claim 14 wherein said charge rate is determined over a time period beginning when the capacitor is not fully discharged and has a minimum charge differential across the capacitor so that upon initiation of an episodic charging event, the storage capacitor is discharged to at least said predetermined minimum.

21. The process of claim 5 wherein internal impedance is compared.

22. The process of claim 7 wherein attainment of a predetermined amount of expended energy from said battery causes an ERT flag to be effected.

23. The process of claim 22 wherein a charge time measurement is used to create said ERT flag.

24. The process of claim 23 wherein said ERT flag is transmitted to a programmer.

25. The process of claim 16 wherein the pacing currents are selected from the group consisting of pacing rate, pacing mode, lead impedance, pulse width, and pulse amplitude.

26. The process of claim 17 wherein said battery comprises a battery characterized by having an internal impedance characteristic curve which is initially substantially linear as a function of energy depletion, but which asymptotically approaches an energy production limit and increasing internal impedance.

27. The process of claim 26 wherein said battery comprises a lithium battery.

30. The system of claim 29, wherein the rate of charge storage is correlated to a value of internal battery resistance through a charge depletion vs. battery resistance mathematical model.

31. The system of claim 29, wherein the first device has a plurality of relatively quiescent periods and the storage capacitor is adapted to provide a basis of determining the rate of charge storage during one of the relatively quiescent periods.

32. The system of claim 29, wherein the predetermined set of charge time measurement set-up parameters include:

a physician-programmed final voltage (V_F) to end a time measurement for determining the rate of charge storage in the capacitor; and

an initial reference voltage (V_I) to begin the time measurement for determining the rate of charge storage in the capacitor,

wherein a pacing supply storage voltage (V_cs) increases approximately linearly from V_I to V_F during the time measurement for determining the rate of charge storage in the capacitor.

33. The system of claim 32, wherein:

the at least one second device includes a multiplexer for selecting one of VF and VI to be compared to a capacitor voltage level (Vsc) for controlling current flow from the battery power terminal to the capacitor; and

the at least one second device selects VI to be compared to Vsc to begin a time charge measurement count and VF to be compared to Vsc to end the time charge measurement count.

34. The system of claim 29, wherein the at least one second device is adapted to declare an ERT if N previous measurements are greater than the ERT charge time limit.

35. The system of claim 29, wherein a device operating current rage is subdivided into current range bins, each bin having a battery charge depletion target and a battery resistance ERT target, each bin further having a predetermined set of charge time measurement set-up parameters and a predetermined ERT charge time limit determined from the battery charge depletion target and the battery resistance ERT target.

36. The system of claim 29, wherein the rate of charge storage is correlated to a value of internal battery resistance through a charge depletion vs. battery resistance mathematical model.

37. The system of claim 29, wherein the at least one second device includes a time charge counter for measuring a time in which a relatively constant current charges the capacitor from an initial reference voltage (VI) to a physician-programmed final voltage (VF).

39. The pacemaker of claim 38, wherein the pacemaker control circuitry includes comparison circuitry for comparing a battery terminal voltage (Vbatt) to a brownout voltage limit (Vstop), and for comparing a PSS capacitor voltage (Vcs) to one of the predetermined set of charge time measurement set-up parameters.

40. The pacemaker of claim 39, wherein the pacemaker control circuitry further includes a switched capacitor power supply operably connected to the battery power terminal and the PSS capacitor for charging the PSS capacitor, wherein an output of the comparison circuit is electrically connected to the switched capacitor power supply to control current flow from the battery power terminal to the pacing supply storage capacitor.

41. The pacemaker of claim 38, wherein the predetermined set of charge time measurement set-up parameters include:

a physician-programmed final voltage (VF) to end a time measurement for determining the rate of charge storage in the PSS capacitor; and

an initial reference voltage (VI) to begin the time measurement for determining the rate of charge storage in the PSS capacitor.

42. The pacemaker of claim 41, wherein a pacing supply storage voltage (Vcs) increases approximately linearly from VI to VF during the time measurement for determining the rate of charge storage in the PSS capacitor.

43. The pacemaker of claim 41, wherein:

the CTM control circuitry includes a multiplexer for selecting one of VF and VI to be compared to a PSS capacitor voltage level (Vsc) within the pacemaker control circuitry for controlling current flow from the battery power terminal to the PSS capacitor; and

the CTM control circuitry selects VI to be compared to Vsc to begin a time charge measurement count and VF to be compared to Vsc to end the time charge measurement count.

44. The pacemaker of claim 41, wherein the CTM control circuitry includes a time charge counter for measuring a time in which a relatively constant current charges the PSS capacitor from VI to VF.

45. The pacemaker of claim 41, wherein the pacemaker control circuitry includes a sensing and pacing control block adapted for selecting VI relative to VF.

46. The pacemaker of claim 41, wherein the pacemaker control circuitry includes a sensing and pacing control block adapted for selecting a voltage level (Vd) to which the PSS capacitor is discharged prior to beginning the time measurement for determining the rate of charge storage in the PSS capacitor.

47. The pacemaker of claim 46, wherein the CTM control circuitry includes a multiplexer for selecting one of the VF, VI and Vd to be compared to a PSS capacitor voltage level (Vsc) within the pacemaker control circuitry for controlling current flow from the battery power terminal to the PSS capacitor.

48. The pacemaker of claim 47, wherein the CTM control circuitry is adapted to select:

VF to be compared to Vsc to synchronize the beginning of the time measurement to the completion of a cardiac depolorization;

Vd to be compared to Vsc to limit the discharge of the PSS capacitor and open a PSS capacitor discharge switch;

VI to be compared to Vsc to begin a time charge measurement count after a bypass capacitor (Cb) is discharged and a battery terminal voltage (Vbatt) is driven to a brownout voltage (Vstop) limit; and

VF to be compared to Vsc to end the time charge measurement count.

50. The pacemaker of claim 49, further comprising a switched capacitor power supply operably connected to the battery power terminal and the PSS capacitor for charging the PSS capacitor, wherein an output of the comparison circuit is electrically connected to the switched capacitor power supply to control current flow from the battery power terminal to the pacing supply storage capacitor.

51. The pacemaker of claim 50, wherein the predetermined set of charge time measurement set-up parameters include:

a physician-programmed final voltage (VF) to end a time measurement for determining the rate of charge storage in the PSS capacitor; and

an initial reference voltage (VI) to begin the time measurement for determining the rate of charge storage in the PSS capacitor.

52. The pacemaker of claim 51, wherein a pacing supply storage voltage (Vcs) increases approximately linearly from VI to VF during the time measurement for determining the rate of charge storage in the PSS capacitor.

53. The pacemaker of claim 51, wherein:

the CTM control circuitry includes a multiplexer for selecting one of VF and VI to be compared to a PSS capacitor voltage level (Vsc) within the pacemaker control circuitry for controlling current flow from the battery power terminal to the PSS capacitor; and

the CTM control circuitry selects VI to be compared to Vsc to begin a time charge measurement count and VF to be compared to Vsc to end the time charge measurement count.

54. The pacemaker of claim 51, wherein the CTM control circuitry includes a time charge counter for measuring a time in which a relatively constant current charges the PSS capacitor from VI to VF.

55. The pacemaker of claim 51, wherein the pacemaker control circuitry includes a sensing and pacing control block adapted for selecting a voltage level (Vd) to which the PSS capacitor is discharged prior to beginning the time measurement for determining the rate of charge storage in the PSS capacitor.

56. The pacemaker of claim 55, wherein the CTM control circuitry includes a multiplexer for selecting one of the VF, VI and Vd to be compared to a PSS capacitor voltage level (Vsc) within the pacemaker control circuitry for controlling current flow from the battery power terminal to the PSS capacitor.

57. The pacemaker of claim 56, wherein the CTM control circuitry selects:

VF to be compared to Vsc to synchronize the beginning of the time measurement to the completion of a cardiac depolorization;

Vd to be compared to Vsc to limit the discharge of the PSS capacitor and open a PSS capacitor discharge switch;

VI to be compared to Vsc to begin a time charge measurement count after a bypass capacitor (Cb) is discharged and a battery terminal voltage (Vbatt) is driven to a brownout voltage (Vstop) limit; and

VF to be compared to Vsc to end the time charge measurement count.

59. The system of claim 58, wherein the programer is adapted to determine the battery resistance by calculating the battery resistance using the determined rate of charge storage and the predetermined set of charge time measurement set-up parameters.

60. The system of claim 58, wherein the programer is adapted to determine the battery resistance by a table look-up using the determined rate of charge storage and the predetermined set of charge time measurement set-up parameters.

61. The system of claim 58, wherein the programmer is further adapted to estimate and display charge remaining in the battery.

62. The system of claim 58, wherein the programmer is further adapted to estimate a time until the pacemaker declares an ERT.

16. A process for indicating estimated replacement time for a battery in a cardiac pacing system, said system having a) a battery, b) a device which delivers electric current to a patient, which device is powered by said battery in an episodic manner, and c) a means which is capable of estimating pacing current, whereby after estimating said pacing current, the estimated current is considered with programmed pulse rates or programmed pace rates in said cardiac pacing system to estimate a replacement time for said battery.

17. A process for estimating a level of energy depletion in a system having a battery, a device which is powered by said battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

a) reading the rate of charge storage or

b) measuring both time and charge stored or added to said charge storage capacitor so that a rate of charge storage may be calculated,

said process comprising

i) finding a relatively quiescent period in powering of said device in said episodic manner,

ii) determining a rate of charging in said storage capacitor during said quiescent period,

iii) correlating said rate of charging in said storage capacitor to a value of internal resistance in said battery through a comparison with known relationships for said battery and rate of charging to determine a value for the internal resistance of said battery.

28. A system having a battery characterized by having an internal resistance characteristic curve which is initially substantially linear as a function of energy depletion, but which asymptotically approaches an energy production limit and increasing internal resistance, a device which is powered by said battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

e) reading the rate of charge storage or

f) measuring both time and charge stored or added to said charge storage capacitor so that a rate of charge storage may be calculated.

29. A system comprising:

a lithium battery having an internal resistance;

a charge storage capacitor electrically connected to said lithium battery;

a first device electrically connected to said lithium battery and adapted to be powered by said battery; and

at least one second device electrically connected to said charge storage capacitor,

wherein the at least one second device is adapted to;

access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit determined from a battery resistance ERT target that corresponds to a battery charge depletion target;

determine a rate of charge storage in the capacitor using the predetermined set of charge time measurement set-up parameters;

compare the determined rate of charge storage in the capacitor to the predetermined ERT charge time limit for the predetermined set of charge time measurement set-up parameters; and

declare an ERT based on a number of comparisons between the determined rate of charge storage in the capacitor and the ERT charge time limit.

38. A pacemaker, including:

a battery power terminal for a pacemaker battery;

a pacing supply storage (PSS) capacitor electrically connected to the battery power terminal;

pacemaker control circuitry electrically connected to the battery power terminal and the PSS capacitor for controlling current flow from the battery power terminal to the PSS capacitor; and

charge time measurement (CTM) control circuitry electrically connected to the pacemaker control circuitry and adapted to;

access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit determined from a battery resistance ERT target that corresponds to a battery charge depletion target;

determine a rate of charge storage in the PSS capacitor using the predetermined set of charge time measurement set-up parameters;

compare the determined rate of charge storage in the PSS capacitor to the predetermined ERT charge time limit for the predetermined set of charge time measurement set-up parameters; and

declare an ERT based on a number of comparisons between the determined rate of charge storage in the PSS capacitor and the ERT charge time limit.

49. A pacemaker, including:

a battery power terminal for a pacemaker battery;

sensing and pacing control circuitry electrically connected to the battery power terminal;

a pacing supply storage (PSS) capacitor electrically connected to the battery power terminal and to a discharge switch;

comparison circuitry, including;

a first comparator electrically connected to the battery power terminal and adapted for comparing a battery terminal voltage (Vbatt) to a brownout voltage (Vstop), the first comparator having a first comparator output;

a second comparator electrically connected to the PSS capacitor and adapted for comparing a pacing supply storage voltage (Vcs) to at least one reference voltage (Vx), the second comparator having a second comparator output, wherein the first comparator output and the second comparator output are adapted to control current flow from the battery power terminal to the PSS capacitor; and

charge time measurement (CTM) control circuitry electrically connected to the sensing and pacing control circuitry, the comparator circuitry and the discharge switch, the charge time measurement control circuitry being adapted to;

access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit determined from a battery resistance ERT target that corresponds to a charge depletion target;

determine a rate of charge storage in the PSS capacitor using the predetermined set of charge time measurement set-up parameters;

compare the determined rate of charge storage in the PSS capacitor to the predetermined ERT charge time limit for the predetermined set of charge time measurement set-up parameters; and

declare an ERT based on a number of comparisons between the determined rate of charge storage in the charge storage capacitor and the ERT charge time limit.

58. A system, including:

a pacemaker, including;

a battery power terminal for a pacemaker battery;

a pacing supply storage (PSS) capacitor electrically connected to the battery power terminal;

pacemaker control circuitry electrically connected to the battery power terminal and the PSS capacitor for controlling current flow from the battery power terminal to the PSS capacitor; and

charge time measurement (CTM) control circuitry electrically connected to the control circuitry and adapted to;

access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit determined from a battery resistance ERT target that corresponds to a charge depletion target;

determine a rate of charge storage in the PSS capacitor using the predetermined set of charge time measurement set-up parameters;

compare the determined rate of charge storage in the PSS capacitor to the predetermined ERT charge time limit for the predetermined set of charge time measurement set-up parameters; and

declare an ERT based on a number of comparisons between the determined rate of charge storage in the PSS capacitor and the ERT charge time limit; and

a programmer adapted to communicate with the pacemaker, the programmer being adapted to use the determined rate of charge storage and the predetermined set of charge time measurement set-up parameters to assess battery condition by determining the battery resistance.