Method and apparatus for determining depleted capacity of a battery

• US 20030149455A1
• Filed: 11/13/2002
• Published: 08/07/2003
• Est. Priority Date: 12/19/2000
• Status: Active Grant

• Current Assignee: St. Jude Medical AB (Abbott Laboratories Incorporated)
• Original Assignee: St. Jude Medical AB (Abbott Laboratories Incorporated)
• Inventors: Obel, Martin, Lindberg, Jan
• Granted Patent: US 7,058,451 B2
• Time in Patent Office: Days
• US Class Current: 607/27
• CPC Class Codes: A61N 1/3708 for power depletion
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/378 specially adapted for the type of battery or accumulator
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

A method of detecting the status of the battery of an implantable heart stimulator comprises the steps of measuring the impedance of the battery, detecting an increased value of the measured impedance, determining an impedance based value of the remaining capacity of the battery from the detected impedance increase, combined with the steps of measuring the total charge depleted from the battery, and determining a charge depletion based value of the remaining capacity of the battery. A battery status detecting circuit for an implantable heart stimulator includes a first measurement means (12) for measuring the impedance of the battery (6), a detection means (14) for detecting an increased value of the measured impedance, a first determination means (16) for determining an impedance based value of the remaining capacity of the battery from the detected impedance increase. A second measurement means (22) is provided for measuring the total charge depleted from the battery, and a second determination means (24) is provided for determimng a charge depletion based value of the remainig battery capacity.

Claims

1. A method for determining depleted capacity of a battery of CF_x type used in an implantable medical device, characterized in that average values of battery voltage and current drawn from the battery (2) are measured during a measurement time, the length of which exceeds a battery voltage recovery time after a load change, and in that predetermined relations between, on one hand, combinations of average values of voltage and current and, on the other, depleted battery capacity are used for determining depleted capacity of the battery from said measured average voltage and current.

2. The method according to claim 1, characterized in that said measurement time exceeds the battery recovery time by a predetermined factor.

3. The method according to claim 2, characterized in that said factor equals a number between 5 and 10.

4. The method according to any one of the preceding claims, characterized in that said battery recovery time equals a time within the range 3-50 h.

5. The method according to any one of the preceding claims, characterized in that said measurement time exceeds 24 h.

6. The method according to any one of the preceding claims, characterized in that said average values of voltage and current are entered into a predetermined look-up table providing depleted battery capacity for different average voltage and current combinations.

7. The method according to any one of the preceding claims, characterized in that depleted battery capacity is also determined by time integrating the total current drawn from the battery.

8. The method according to claim 7, characterized in that an alarm is triggered if the difference between depleted battery capacities, determined from measured average values of battery voltage and current and determined by time integration of the current drawn from the battery, respectively, exceeds a predetermined threshold value.

9. An apparatus for determining depleted capacity of a battery of CF_x type used in an implantable medical device, characterized in that averaging means (10,12) are provided to determine average values of battery voltage and current drawn from the battery during a measurement time, the length of which exceeds a battery voltage recovery time after a load change, and in that a determining means is provided for determining actual depleted battery capacity from predetermined relations between, on one hand, combinations of average values of voltage and current and, on the other, depleted battery capacity.

10. The apparatus according to claim 9, characterized in that said predetermined relations include a stored, predetermined look-up table of depleted battery capacity for different combinations of average voltage and current and in that said determining means is adapted to enter combinations of measured average voltage and current values into said look-up table to determine actual depleted battery capacity.

11. The apparatus according to claim 9 or 10, characterized in that said averaging means (10.12) are adapted to determine said average values by sampling and integrating battery voltage and current during said measurement time.

12. The apparatus according to claim 9 or 10, characterized in that said determining means comprises an integrating means for integrating the total current drawn from the battery to determine total charge depleted from the battery.

13. The apparatus according to any one of the claims 9 through 12, characterized in that an impedance measurement means is provided to measure the internal battery impedance when depleted battery capacity reaches a predetermined threshold value, determined from measured average values of battery voltage and current, and in that a second determining means is provided to thereafter determine depleted battery capacity from the measured internal impedance.

14. The apparatus according to claim 13, characterized in that a first trigger ming means is provided to trigger said impedance measurement means when depleted battery capacity reaches said predetermined threshold value, determined from measured average values of battery voltage and current, of depleted battery capacity.

15. The apparatus according to any one of the claims 9-11 and one or more of the claims 12-14, characterized in that a second triggering means is triggering an alarm if the difference between depleted battery capacities, determined from measured average values of battery voltage and current, and determined by time integration of the current drawn from the battery or determined from the measured internal impedance, respectively, exceeds a predetermined threshold value.

16. A pacemaker, characterized by an apparatus according to any one of the claims 9-15.