Battery status indicator compensating for battery voltage recovery

• US 20060197536A1
• Filed: 03/03/2005
• Published: 09/07/2006
• Est. Priority Date: 03/03/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Gandhi, Rajesh, Kelley, Shawn, James, Kristofer, McNamee, Paul, Dyjach, John
• Granted Patent: US 7,355,376 B2
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: A61N 1/3708 for power depletion
• 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: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: Y10S 320/11 Prioritized supply of power or power supply compensation

Abstract

A method for determining a recovery voltage in a battery includes detecting a transient increased current draw event drawing current from the battery, the transient increased current draw event starting at a start time and ending at an end time; and in response to detecting the transient increased current draw event, waiting until time and/or voltage criteria are met to determine recovered battery voltage. An implantable pulse generator (PG) device for stimulating a human organ includes a battery, a power sink drawing current from the battery, wherein drawing increased current from the battery for transient periods causes battery voltage to decrease; and a status indicator detecting a transient increased current draw event and waiting a minimum time duration after the transient increased current draw event to measure battery voltage in order to determine a recovery voltage.

Claims

1. A method for determining a recovery voltage associated with a battery, the method comprising:

detecting a transient increased current draw event that draws current from the battery at a current level that is greater than a steady-state average current level, the transient increased current draw event starting at a start time and ending at an end time;

selecting a battery voltage measurement obtained after the end time based on time-related or voltage-related criteria; and

determining the recovery voltage using the battery voltage measurement, wherein the recovery voltage represents a voltage level to which battery voltage is expected to recover after the transient increased current draw event.

2. A method as recited in claim 1 wherein selecting comprises:

determining a time duration to wait prior to obtaining the battery voltage measurement, wherein the time duration is determined based on one or more battery conditions including battery chemistry, type of transient increased current draw event, duration of the transient increased current draw event, magnitude of voltage change during the transient increased current draw event, and temperature; and

measuring battery voltage after the time duration has passed.

3. A method as recited in claim 2 further comprising:

obtaining multiple battery voltage measurements at predetermined time intervals after the time duration has passed; and

wherein determining the recovery voltage comprises fitting multiple voltage measurements to a curve.

4. A method as recited in claim 1 wherein selecting a measured battery voltage comprises obtaining multiple battery voltage measurements at associated times after the end time, wherein intervals between adjacent times are determined according to a function.

5. A method as recited in claim 1, further comprising taking a derivative of voltage with respect to time.

6. A method as recited in claim 5 further comprising taking a multiple order derivative with respect to time.

7. A method as recited in claim 1 further comprising:

obtaining an initial voltage measurement prior to the transient increased current draw event; and

wherein the voltage-criteria specifies a minimum threshold voltage difference; and

wherein determining the recovery voltage comprises setting the recovery voltage equal to the battery voltage measurement if the difference between the initial voltage measurement and the battery voltage measurement is less than or equal to the minimum threshold voltage difference.

8. A computer-readable medium having processor-executable instructions, which when executed by a processor cause the processor to perform a process for determining a recovery voltage associated with a battery, the process comprising:

detecting a transient increased current draw event that draws current from the battery at a current level that is greater than a steady-state average current level, the transient increased current draw event starting at a start time and ending at an end time;

obtaining a first measured battery voltage at a first measurement time after the end time;

obtaining a subsequent measured battery voltage at a subsequent measurement time after the first measurement time; and

determining the recovery voltage by determining whether the difference between the first measured battery voltage and the subsequent measured battery voltage is less than a specified voltage change.

9. A method as recited in claim 8 further comprising:

iteratively obtaining one or more other subsequent measured battery voltages at corresponding subsequent measurement times after the end time, wherein time durations between adjacent subsequent measurement times are variable; and

comparing successive differences between subsequent measured battery voltages to determine if a change in battery voltage is less than the specified voltage change.

10. A method as recited in claim 8 further comprising:

determining an estimated recovery voltage based on a function of the first measured battery voltage and the subsequent measured battery voltage measured; and

if time between the subsequent measurement time and the end time is greater than a specified maximum time, using the estimated recovery voltage to determine charge remaining in the battery.

11. A method as recited in claim 8 further comprising:

obtaining an initial battery voltage measurement prior to the start time;

determining whether a magnitude of difference between the initial battery voltage and a selected one of the first measured battery voltage and the subsequent measured battery voltage is less than a specified threshold value; and

if the magnitude of difference is less than the specified threshold value, setting the recovery voltage equal to the selected one of the first measured battery voltage and the subsequent measured battery voltage.

12. An implantable pulse generator (PG) device operable to stimulate an organ, the PG device comprising:

a battery;

a power sink drawing current from the battery at a steady-state level when a high current function is deactivated and drawing current from the battery at an increased level when the high current function is activated, wherein drawing current at the increased level causes a drop in battery voltage and a subsequent return to drawing current at the steady-state level causes an increase in battery voltage toward a recovery voltage;

a control module controlling the power sink and triggering a transient increased current draw event comprising drawing current at the increased level for a time period followed by drawing current at the steady-state level; and

a status indicator module detecting the transient increased current draw event and waiting a minimum time duration after the transient increased current draw event to determine the recovery voltage.

13. A PG device as recited in claim 12, further comprising:

a memory having stored thereon a value representing a time duration, and wherein the status indicator module determines the minimum time by retrieving the value from the memory.

14. A PG device as recited in claim 12 wherein the status indicator module determines the recovery voltage based on a rate of change in battery voltage during a voltage recovery period after the transient increased current draw event.

15. A PG device as recited in claim 14 wherein the status indicator module measures multiple voltages, each of the multiple voltages measured at a time determined according to a function of a minimum time increment, and wherein the time interval between each voltage measurement is variable.

16. A PG device as recited in claim 12 wherein the power sink comprises one or more of a beeper, telemetry circuitry, or a high-voltage charge circuitry.

17. A PG device as recited in claim 12 wherein the status indicator module measures multiple voltages taken at predetermined time intervals during a voltage recovery period and predicts the recovery voltage based on the multiple voltage measurements.

18. A PG device as recited in claim 17 wherein the status indicator module predicts the recovery voltage by fitting the multiple voltage measurements to a curve.

19. A PG device as recited in claim 17 wherein the status indicator module predicts the recovery voltage based on one or more of the multiple voltage measurements, the battery voltage prior to the transient increased current draw event, the duration of the event, the magnitude of charge used during the event.

20. A system comprising:

a power sink requiring power to operate;

a battery delivering increased current to the power sink at a specified time, wherein delivery of increased current to the power sink causes a drop in battery voltage and a subsequent voltage recovery; and

means for determining a recovery voltage including computing a rate of change of voltage during the voltage recovery.

21. A system as recited in claim 20, wherein the means for determining comprises:

a memory having stored thereon microprocessor-executable instructions; and

a microprocessor retrieving the instructions from the memory.

22. A system as recited in claim 20, wherein the means for determining implements a method comprising:

determining an absolute value of the difference between a first voltage measurement and a second voltage measurement;

if the absolute value of the difference is less than a specified voltage difference, using the second voltage measurement to determine remaining charge in the battery;

if the absolute value of the difference is not less than the specified voltage difference, computing an estimated recovery voltage based on at least a function of the first and second voltage measurements; and

if the elapsed time since the specified time is greater than a maximum time, using the estimated recovery voltage to determine remaining charge in the battery.

23. A system as recited in claim 20 wherein the means for determining a recovery voltage comprises determining a minimum time to wait after delivering increased current before measuring battery voltage, and wherein the minimum time to wait is based on at least one of the magnitude of the drop in battery voltage, the type of battery, the length of time of delivery of current to the power sink, and the type of power sink.