Abstract:
A power management system and technique to manage and allocate the energy provided to various components of an implanted device during periods of low energy. The power management system includes an implantable power source delivering energy to various components within the implantable medical device, a measurement device to measure the energy of the power source, and a processor responsive to the measurement device. The processor monitors the energy level of the power source. During periods of low energy, the processor limits the energy to certain device-critical components of the implantable medical device. This minimizes the risk of damage to the power source resulting from high energy drain during periods of low energy. Further, this preserves operation of device-critical components of the implanted device during periods of low energy.

Description:
BACKGROUND OF THE INVENTION 
     This patent application is related to the following patent applications filed herewith: 
     (1) U.S. patent application Ser. No. 09/561,566, entitled “Implantable Medical Pump with Multi-layer Back-up Memory,” filed on Apr. 28, 2000, and having named inventors David C. Ullestad and Irfan Z. Ali; 
     (2) U.S. patent application Ser. No. 09/562,221, entitled “Battery Recharge Management for an Implantable Medical Device,” filed on Apr. 28, 2000, and having named inventors Nathan A. Torgerson and James E. Riekels; and 
     (3) U.S. patent application Ser. No. 09/561,479, entitled “Method and Apparatus for Programming an Implantable Medical Device,” filed on Nov. 1, 2001. 
     FIELD OF INVENTION 
     This invention relates generally to implantable medical devices, and more particularly to power management techniques for implantable medical devices. 
     DESCRIPTION OF THE RELATED ART 
     The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Physicians use medical devices alone or in combination with drug therapies to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. 
     Implantable medical devices are commonly used today to treat patients suffering from various ailments. Implantable medical devices can be used to treat any number of conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson&#39;s disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of implantable medical device therapies has expanded, greater demands have been placed on the implantable medical device. 
     One type of implantable medical device is an Implantable Neuro Stimulator (INS). The INS delivers mild electrical impulses to neural tissue using an electrical lead. The neurostimulation targets desired neural tissue to treat the ailment of concern. For example, in the case of pain, electrical impulses (which are felt as tingling) may be directed to cover the specific sites where the patient is feeling pain. Neurostimulation can give patients effective pain relief and can reduce or eliminate the need for repeat surgeries and the need for pain medications. 
     Implantable medical devices such as neurostimulation systems may be partially implantable where a power source is worn outside the patient&#39;s body. This system requires an antenna to be placed on the patient&#39;s skin over the site of the receiver to provide energy and control to the implanted device. Typically, the medical device is totally implantable where the power source is part of the implanted device. The physician and patient may control the implanted system using an external programmer. Such totally implantable systems include, for example, the Itre® 3 brand neurostimulator sold by Medtronic, Inc. of Minneapolis, Minn. 
     In the case of an INS, for example, the system generally includes an implantable neurostimulator (INS) (also known as an implantable pulse generator (IPG)), external programmer(s), and electrical lead(s). The INS is typically implanted near the abdomen of the patient. The lead is a small medical wire with special insulation. It is implanted next to the spinal cord through a needle and contains a set of electrodes (small electrical contacts) through which electrical stimulation is delivered to the spinal cord. The lead is coupled to the INS via an implanted extension cable. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. The INS contains electronics to send precise, electrical pulses to the spinal cord, brain, or neural tissue to provide the desired treatment therapy. The external programmer is a hand-held device that allows the physician or patient to optimize the stimulation therapy delivered by the INS. The external programmer communicates with the INS using radio waves. 
     Totally implantable medical devices, however, rely entirely on the implanted power source. Various INS components rely on the power source for energy, including for example, the signal generator for providing treatment therapy to the patient, the real time clock, the telemetry unit, and the memory. The signal generator is generally the primary energy drain for the power source. For those devices that have nonrechargeable batteries, the batteries last longer, however, the device must be surgically replaced when the power source is fully depleted. For those devices having rechargeable batteries, a surgical procedure is not required, however, the power source must be recharged more frequently since it cannot store as much energy. 
     In known systems, however, the continued operation of the signal generator during times of low energy unnecessarily drains the power source, thereby potentially depleting energy to device-critical INS components, such as the real time clock, the telemetry unit, and the memory. In the event that the power source runs low on energy, the implanted device can lose its treatment efficacy as well as its memory, its time, and its communications link with the external component. Further, when the power source is subsequently recharged, the INS may have to be reprogrammed and recalibrated according to the previous settings that were lost when the power source was fully depleted. The need for energy to handle the various functions of the implanted device is only going to increase. 
     Another disadvantage with known systems is that the power source can be damaged when it is being depleted at a high rate during periods when it has low voltage. This can occur, for example, when the implantable device is operating to provide treatment therapy with INS components having high-power requirements. For example, a 4.0 V battery that is below 2.75 V in stored energy is at risk of being damaged when it is being drained of 4 milliamps of current by the implanted device. Over time, with repeated draining of the battery at these critical setpoints would substantially reduce the efficacy of the battery and ultimately require surgical replacement of the implanted device. 
     Known implantable medical devices, for example, attempt to address the foregoing problems by providing low power or end-of-life warnings to the patient. For example, U.S. Pat. No. 5,344,431 discloses a method and apparatus for determination of battery end-of-service for implantable medical devices. This reference is incorporated herein by reference in its entirety. Such systems, however, continue to drain the battery until it is fully depleted without regard to preserving operation of the device-critical components. 
     Accordingly, there remains a need in that art to provide a power management system and technique for an implantable medical device that maintains operation of device-critical components during periods of low energy. Further, there remains a need in that art to provide a power management system and technique that allocates power source energy during periods of low energy. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique to manage and allocate the energy provided to various components of an implanted device during periods of low energy. In accordance with a preferred embodiment of the present invention, the power management system includes an implantable power source delivering energy to various components within the implantable medical device, a measurement device to measure the energy of the power source, and a processor responsive to the measurement device. The processor monitors the energy level of the power source. If the energy level falls below a first level, the processor shuts off energy to the therapy module of the implantable medical device while continuing to provide energy to the other device-critical components. If the energy level of the power source then falls below a second level, energy to even the device-critical components must be shut off. Eventually, the processor must prepare the entire implantable medical device to shut down. During recharge, when the energy level of the power source reaches a certain level, energy to all components is resumed. 
     Advantageously, this power management system and technique minimizes the risk of damage to the power source resulting from high energy drain during periods of low energy. Further, the present invention provides a technique to preserve operation of device-critical components of the implanted device during periods of low energy. 
     In alternative embodiments, the power management system of the present invention can be used with any number of implantable systems requiring a self-contained power source, including, but not limited to, pacemakers, defibrillators, and cochlear implants. In another alternative embodiment, the power management system of the present invention may be used with implantable diagnostic devices for detecting bodily conditions of certain organs, like the brain or the heart. In yet another alternative embodiment, the power management system of the present invention can be used within a drug delivery system having an implantable battery-powered pump. The power source in any of the these embodiments may be rechargeable or non-rechargeable. If rechargeable, the power source may be a lithium ion battery. The power source may also be a capacitive power source or any other source. The present invention serves to manage the energy of any of these power sources and to efficiently allocate the energy during times of low energy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an implantable medical device in accordance with a preferred embodiment of the present invention, as implanted in a human body; 
     FIGS. 2A-D illustrates locations where the implantable medical device of the present invention can be implanted in the human body other than the location shown in FIG. 1; 
     FIG. 3 is a schematic block diagram of an INS in accordance with a preferred embodiment of the present invention; 
     FIG. 4 depicts a general operation flowchart of the INS in accordance with a preferred embodiment of the present invention; 
     FIG. 5 is a schematic block diagram of the power management module in accordance with a preferred embodiment of the present invention; 
     FIG. 6 is a flow chart depicting the operation of the power management module in accordance with a preferred embodiment of the present invention; 
     FIG. 7 is a chart depicting the change in power source energy over time for an implanted medical device in accordance with the present invention; and 
     FIG. 8 is a chart depicting energy over time for an implanted medical device as the power source is being recharged from a depleted state. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is an power management system and method for an implantable medical device. The power management system provides an allocation of energy during periods when the implanted device has limited energy. In the preferred embodiment, the present invention is implemented within an implantable neurostimulator, however, those skilled in the art will appreciate that the present invention may be implemented generally within any implantable medical device having an implanted power source. 
     FIG. 1 shows the general environment of an Implantable Neuro Stimulator (INS) medical device  14  in accordance with a preferred embodiment of the present invention. The neurostimulation system generally includes an INS  14 , a lead  12 , a lead extension  20 , an External Neuro Stimulator (ENS)  25 , a physician programmer  30 , and a patient programmer  35 . The INS  14  preferably is a modified implantable pulse generator that will be available from Medtronic, Inc. with provisions for multiple pulses occurring either simultaneously or with one pulse shifted in time with respect to the other, and having independently varying amplitudes and pulse widths. The INS  14  contains a power source  315  and electronics to send precise, electrical pulses to the spinal cord, brain, or neural tissue to provide the desired treatment therapy. The power source  315  is discussed in further detail herein. As preferred, INS  14  provides electrical stimulation by way of pulses although other forms of stimulation may be used such as continuous electrical stimulation. 
     The lead  12  is a small medical wire with special insulation. The lead  12  includes one or more insulated electrical conductors with a connector on the proximal end and electrical contacts on the distal end. Some leads are designed to be inserted into a patient percutaneously, such as the Model 3487A Pisces-Quad® lead available from Medtronic, Inc. of Minneapolis Minn., and some leads are designed to be surgically implanted, such as the Model 3998 Specify® lead also available from Medtronic. The lead  12  may also be a paddle having a plurality of electrodes including, for example, a Medtronic paddle having model number 3587A. In yet another embodiment, the lead  12  may provide electrical stimulation as well as drug infusion. Those skilled in the art will appreciate that any variety of leads may be used to practice the present invention. 
     The lead  12  is implanted and positioned to stimulate a specific site in the spinal cord or the brain. Alternatively, the lead  12  may be positioned along a peripheral nerve or adjacent neural tissue ganglia like the sympathetic chain or it may be positioned to stimulate muscle tissue. The lead  12  contains one or more electrodes (small electrical contacts) through which electrical stimulation is delivered from the INS  14  to the targeted neural tissue. If the spinal cord is to be stimulated, the lead  12  may have electrodes that are epidural, intrathecal or placed into the spinal cord itself. Effective spinal cord stimulation may be achieved by any of these lead placements. 
     Although the lead connector can be connected directly to the INS  14 , typically the lead connector is connected to a lead extension  20  which can be either temporary for use with an ENS  25  or permanent for use with an INS  14 . An example of the lead extension  20  is Model 7495 available from Medtronic. 
     The ENS  25  functions similarly to the INS  14  but is not designed for implantation. The ENS  25  is used to test the efficacy of stimulation therapy for the patient before the INS  14  is surgically implanted. An example of an ENS  25  is a Model 3625 Screener available from Medtronic. 
     The physician programmer  30 , also known as a console programmer, uses telemetry to communicate with the implanted INS  14 , so a physician can program and manage a patient&#39;s therapy stored in the INS  14  and troubleshoot the patient&#39;s INS system. An example of a physician programmer  30  is a Model 7432 Console Programmer available from Medtronic. The patient programmer  35  also uses telemetry to communicate with the INS  14 , so the patient can manage some aspects of her therapy as defined by the physician. An example of a patient programmer  35  is a Model 7434 Itrel® 3 EZ Patient Programmer available from Medtronic. 
     Those skilled in the art will appreciate that any number of external programmers, leads, lead extensions, and INSs may be used to practice the present invention. 
     Implantation of an Implantable Neuro Stimulator (INS) typically begins with implantation of at least one stimulation lead  12  usually while the patient is under a local anesthetic. The lead  12  can either be percutaneously or surgically implanted. Once the lead  12  has been implanted and positioned, the lead&#39;s distal end is typically anchored into position to minimize movement of the lead  12  after implantation. The lead&#39;s proximal end can be configured to connect to a lead extension  20 . If a trial screening period is desired, the temporary lead extension  20  can be connected to a percutaneous extension with a proximal end that is external to the body and configured to connect to an External Neuro Stimulator (ENS)  25 . During the screening period the ENS  25  is programmed with a therapy and the therapy is often modified to optimize the therapy for the patient. Once screening has been completed and efficacy has been established or if screening is not desired, the lead&#39;s proximal end or the lead extension proximal end is connected to the INS  14 . The INS  14  is programmed with a therapy and then implanted in the body typically in a subcutaneous pocket at a site selected after considering physician and patient preferences. The INS  14  is implanted subcutaneously in a human body and is typically implanted near the abdomen of the patient. 
     The above preferred embodiment for the placement of the INS  14  within the lower left abdominal region  6  of the patient is further illustrated in FIG.  2 C. Other preferred embodiments for the placement of stimulator  1  within a human patient is further shown in FIGS. 2A,  2 B, and  2 D. As shown in FIG. 2A, the INS  14  can be implanted in a pectoral region  4  of the patient. As shown in FIG. 2B, the INS  14  can be implanted in a region  5  behind the ear of a patient, and more specifically in the mastoid region. As shown in FIG. 2D, the INS  14  can be placed in the lower back or upper buttock region  7  of the patient. The INS  14  is discussed in further detail herein. 
     The physician periodically uses the physician programmer  30  to communicate with the implanted INS  14  to manage the patient therapy and collect INS data. The patient uses the patient programmer  35  to communicate with the implanted INS  14  to make therapy adjustment that have been programmed by the physician, recharge the INS power source  315 , and record diary entries about the effectiveness of the therapy. Both the physician programmer  30  and patient programmer  35  have an antenna or coil locator that indicates when the telemetry head is aligned closely enough with the implanted INS  14  for adequate telemetry. 
     Optionally, the neurostimulation system may include a sensor  25  to provide closed-loop feedback control of the INS  14 . For example, the INS  14  may receive feedback instructions from an external component, which processes a recorded signal from the sensor  25  and sends instruction to signal generator via antenna or coil. 
     FIG. 3 is a schematic block diagram of an INS  14  in accordance with a preferred embodiment of the present invention. The implantable medical device generally includes a processor  335  with an oscillator  330 , a calendar clock  325 , memory  340 , and system reset  345 , a telemetry module  305 , a recharge module  310 , a power source  315 , a power management module  320 , a therapy module  350 , and a therapy measurement module  335 . Other components of the INS  14  can include, for example, a diagnostics module (not shown). All components except the power source  315  can be configured o n one or more Application Specific Integrated Circuits (ASICs), maybe part of one or more discrete components , or a combination of both . Also, all components except the oscillator  330 , the calendar clock  325 , and the power source  315  are connected to bi-directional data bus  327  that is non-multiplexed with separate address and data lines. The INS  14  generally includes a plurality of device-critical components including the calendar clock  325 , the telemetry module  305 , and the memory  340  (See Table B below). During periods of low energy, these components generally have a higher priority to the energy than other components such as, for example, the therapy module  350 . These components are generally known in the art and are discussed in further detail herein. 
     The processor  335  is synchronous and operates on low energy such as a Motorola  68 HC 11  synthesized core operating with a compatible instruction set. The oscillator  330  operates at a frequency compatible with the processor  335 , associated components, and energy constraints such as in the range from 100 KHz to 1.0 MHZ. The calendar clock  325  counts the number of seconds since a fixed date for date/time stamping of events and for therapy control such as circadian rhythm linked therapies. The memory  340  includes memory sufficient for operation of the INS  14  such as volatile Random Access Memory (RAM) for example Static RAM, nonvolatile Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM) for example Flash EEPROM, and register arrays configured on ASICs. Direct Memory Access (DMA) is available to selected modules such as the telemetry module  305 , so the telemetry module  305  can request control of the data bus  327  and write data directly to memory  340  bypassing the processor  335 . The system reset  345  controls operation of ASICs and modules during power-up of the INS  14 , so ASICs and modules registers can be loaded and brought on-line in a stable condition. 
     Those skilled in the art will appreciate that the INS  14  may be configured in a variety of versions by removing modules not necessary for the particular configuration and by adding additional components or modules. All component of the INS  14  are contained within or carried on a housing that is hermetically sealed and manufactured from a biocompatible material such as titanium. Feedthroughs provide electrical connectivity through the housing while maintaining a hermetic seal, and the feedthroughs can be filtered to reduce incoming noise from sources such as cell phones. 
     FIG. 4 depicts a general operation flowchart of the INS  14 . At step  405 , operation of the INS  14  begins with the processor  335  receiving data from either telemetry module  305  or from an internal source in the INS  14 . At step  410 , the received data is stored in a memory location. At step  415 , the data is processed by the processor  335  to identify the type of data and can include further processing such as validating the integrity of the data. At step  420 , after the data is processed, a decision is made whether to take an action. If no action is required, the INS  14  stands by to receive data. If an action is required, the action will involve one or more of the following modules or components: calendar clock  325 , memory  340 , telemetry  305 , recharge module  310 , power management  320 , therapy module  350 , and therapy measurement  355 . An example of an action would be to recharge the power source  315 . At step  425 , after the action is taken, a decision is made whether the action is to be communicated or “uplinked” to a patient or physician programmer  35  or  30  through the telemetry module  305 . If the action is uplinked, the action is recorded in the patient or physician programmer. If the action is not uplinked, the action is recorded internally within the INS  14 . 
     FIG. 5 depicts a block diagram of the power management module  320  in accordance with a preferred embodiment of the present invention. The power management module  320  provides a stable DC power source to the INS  14  with voltages sufficient to operate the INS  14  such as between about 1.5 VDC and 2.0 VDC. The power management module  320  includes a first DC to DC converter  505 , a second DC to DC converter  510 , and power source measurement unit  515 . One or more additional DC to DC converters can be added to the power management module  320  to provide additional voltage values for the INS  14 . The first DC to DC converter  505  and second DC to DC converter  510  can be operational amplifiers configured for a gain necessary for the desired output voltage. The power source measurement unit  515  measures the power source  315  and reports this measurement to the processor  335 , so the processor  335  can determine how to best allocate the power source  315 , if necessary. In accordance with the present invention, if the processor  335  determines that the power source  315  is inadequate for normal operation, the processor  335  can instruct the power management module  320  to limit the energy to the device critical-components of the INS  14  or even to initiate a controlled shutdown of the INS  14 . This process is discussed in further detail herein. 
     The INS power source  315  typically provides a voltage sufficient for the power management module  320  to supply energy to the INS  14  such as above 2.0 VDC, providing a maximum current in the range from about 5.0 mA to 30.0 mA for a time period adequate for the intended therapy. The INS power source  315  can be a physical storage source such as a capacitor or super capacitor, or the power source can be a chemical storage source such as a battery. The INS power source  315  can be a hermetically sealed rechargeable battery such as a lithium ion (Li+) battery or a non-rechargeable battery such as a lithium thionyl chloride battery. The ENS battery can be a non-hermetically sealed rechargeable battery such as nickel cadmium or a non-rechargeable battery such as an alkaline. 
     FIG. 6 is a flow chart depicting the operation of the power management module  320  in accordance with a preferred embodiment of the present invention. At step  605 , the power management module  320  receives input energy from the power source. At steps  610  and  615 , the energy is provided to DC to DC converters  505  and  510  before it is delivered, at steps  625  and  630 , to various components within the INS  14 . Also, at step  620 , the power source measurement unit  515  measures the power source  315  and, at step  635 , provides that information to the processor  335 . The processor  335 , in turn, determines how the energy from the power source  315  will be allocated, in accordance with procedures discussed herein, as a function of the battery voltage. 
     FIG. 7 is a chart depicting the change in power source energy over time for an implanted medical device in accordance with the present invention. The chart depicts the power source  315  being fully charged to being completely depleted. As shown in example of FIG. 7, at time t=0, the power source  315  is fully charged at 4.05 V (for a lithium ion power source). The voltage decreases over time, at first, gradually but rather precipitously after a certain point in time. The processor  335  periodically monitors the power source  315  and reacts accordingly as described herein. At a first transition point T 1 , the voltage is sufficiently low such that it becomes necessary to begin the process of limiting resources to the device-critical components of the INS  14 . For a lithium ion battery as the power source  335 , this first transition point T 1  preferably is approximately 3.6 V and may be in the range of 3.85 V to 3.25 V. At a voltage of approximately 3.6 V, the INS  14  operates in a low power mode by restricting the energy provided to the INS components. In particular, energy is limited to the device-critical components such as the calendar clock  325 , the telemetry unit  305 , and the memory  340 , while energy to the therapy module  350  and other components is suspended (See Table B below). In particular, energy is suspended to all unnecessary energy drains, such as unneeded level shifters. At the first transition point T 1 , the operation of the therapy module  350  to provide treatment therapy to the patient is suspended in efforts to preserve energy. Further, the INS  14  stores unsaved data in the memory  340  and the time/date of the calendar clock  325  into nonvolatile memory (such as an electrically erasable programmable read-only memory (EEPROM)) in the event that the power source  315  is drained completely. Data that may be stored in EEPROM may include, for example, new parameter data, measurement data, and patient information. Register values from therapy module  350  may also be stored in EEPROM. The processor  335  will also move into a sleep mode. 
     During this time period, since the treatment therapy has been suspended, it is anticipated that the patient will realize that the power source  315  is low and will recharge or replace the power source  315  to resume the treatment therapy. Alternatively, warning thresholds may be determined to give the patient warnings about depletion of the power source  315  as the power source  315  nears the first transition point T 1 . For example, warnings may be provided through the patient programmer  35  or an INS beeper. 
     During this period, if the INS  14  is interrogated by an external component, the INS  14  will provide a signal informing the external component that the power source  315  is near depletion or that it needs recharging. 
     If the power source  315  continues to drain in energy past a second transition point T 2 , the INS  14  must prepare to shut down. After this second transition point T 2 , only the recharge module  310  is operable. The recharge module  310  is necessary even at extremely low energy levels to control the recharging process of the power source  315  so as not to damage the power source  315 . Further details of the recharge module  310  is disclosed in U.S. patent application Ser. No. 09/562,221, entitled “Battery Recharge Management Method and Apparatus for an Implantable Medical Device,” having the same inventive entity and the same filing date as that of the present patent application. This co-pending patent application is incorporated herein by reference in its entirety. 
     As preferred, this second transition point T 2  is approximately 1.85 V and may be in the range of 3.20 V to 1.85 V. At this point, the INS  14  preferably stores for a second time the memory  340  and the calendar clock  325  into nonvolatile memory. Advantageously, the storing of calendar clock  325  during the first and second transition points T 1  and T 2  provides information about the power source&#39;s discharge time. 
     The time period between the first and second transition points T 1  and T 2  may range one hour to one year, preferably between 3-6 months. During this time period, the power source  315  has an expected current drain of approximately 6 microamps. In contrast, during the time period before the first transition period, the expected current drain for the power source  315  is approximately 20 microamps to 4 milliamps. The current drain during this time period is much higher due the energy needed to operate the therapy module  350  such as a signal generator. The expected current drain after the second transition point T 2  is approximately 1 microamp or less since almost every INS  14  component has been shut down. Advantageously, this low current drain prevents risk of damage to the power source  315 . 
     The transition points T 1  and T 2  provide boundaries for the three states of operation: (1) normal operation state; (2) low power state; and (3) power off state. These transition points T 1  and T 2  may vary depending upon the type of power source. The following Table A provides the states of operation depending upon the power source: 
     
       
         
               
               
               
               
             
           
               
                 TABLE A 
               
               
                   
               
               
                 Power Source 
                 Normal Operation 
                 Low Power 
                 Power Off 
               
               
                   
               
             
             
               
                 Primary Cell 
                 3.4 V-2.05 V 
                 2.00 V-1.85 V 
                 1.80 V and below 
               
               
                 (CSVO, Hybrid) 
               
               
                 Alkaline 
                 3.0 V (1.5 × 2)-2.0 V 
                 2.00 V-1.85 V 
                 1.80 V and below 
               
               
                 Lithium Ion 
                 4.05 V-3.85 (to 3.25 V) 
                 3.80 V-3.20 V (to 
                 1.80 V and below 
               
               
                   
                   
                 1.85 V) 
               
               
                   
               
             
          
         
       
     
     Table B below lists the components of the INS  14  that active and inactive during each of the three states of operation: 
     
       
         
               
               
               
             
           
               
                 TABLE B 
               
               
                   
               
               
                 State of Operation 
                 Components On 
                 Components Off 
               
               
                   
               
             
             
               
                 Normal Operation 
                 All 
                 None 
               
               
                 Low Power 
                 Power Management 320 
                 Therapy 350 
               
               
                   
                 Recharge 310 
                 Measurement 355 
               
               
                   
                 Telemetry 305 
                 Permanent Memory 
               
               
                   
                 Oscillator 330 
                 Non-volatile Memory 
               
               
                   
                 Calendar Clock 325 
                 EEPROM 
               
               
                   
                 Volatile Memory 
                 Memory Management 
               
               
                   
                 High Freq Protection Circuit 
                 System Bus 327 
               
               
                   
                 High Energy Protection Circuit 
                 Processor 335 
               
               
                   
                 System Shutdown/ POR 345 
               
               
                 Power Off 
                 Recharge 310 
                 Therapy 350 
               
               
                   
                 High Freq. Protection Circuit 
                 Measurement 355 
               
               
                   
                 High Energy Protection Circuit 
                 Permanent Memory 
               
               
                   
                   
                 Non-volatile Memory 
               
               
                   
                   
                 EEPROM 
               
               
                   
                   
                 Memory Management 
               
               
                   
                   
                 System Bus 327 
               
               
                   
                   
                 Processor 335 
               
               
                   
                   
                 Power Management 320 
               
               
                   
                   
                 Telemetry 305 
               
               
                   
                   
                 Oscillator 330 
               
               
                   
                   
                 Calendar Clock 325 
               
               
                   
                   
                 Volatile Memory 
               
               
                   
                   
                 System Shutdown/POR 345 
               
               
                   
               
             
          
         
       
     
     During recharge, a different energy allocation scheme can be implemented during the recharging process. In this regard, FIG. 8 is a chart depicting energy over time for an implanted medical device as the power source  315  is being recharged from a depleted state. The recharging process is achieved by the magnetic recharge energy received from the external component  24 . At a third transition point T 3 , the energy reaches approximately 2.0 V. Before this point, only the recharge module  310  is functional. After this point, each of the INS  14  components that were previously suspended are resumed. After the transition point T 3 , the processor  335  will load configuration data that was stored in the non-volatile memory such as the EEPROM. The processor  335  will also load a battery measurement from the power source measurement  515 . The processor  335  during the recharge process will remain in sleep mode unless a telemetry communication is needed with the external charging device to provide closed-loop charging to maximize time and energy efficiencies. 
     At the fourth transition point T 4 , the power source level is 3.6 V. After this point, the processor  335  may begin operation of the INS  14  to provide treatment therapy. If a system reset is necessary, the treatment parameters stored in EEPROM will be loaded into RAM and the proper registers on the INS  14  to prepare to deliver therapy. 
     When the recharging process is stopped, the processor  335  will wake up to check the power source  315 . If the energy is above 3.6 V, the INS  14  will function in normal operation. If the energy is below 3.6 V, the INS  14  will go into the low power state of operation (described above). 
     Initially, before the INS  14  is first implanted into the patient and charged for the first time, the power source  315  has an initial or a “shipping mode” setting. In shipping mode, the power source  315  is preferably near full charge but is at a low current drain due to the device-critical components. As preferred, the power source  315  is charged to approximately 3.8 V in shipping mode. Advantageously, the INS  14  may be shipped at normal voltage levels such that it may immediately provide treatment therapy upon implant without requiring a charging process. Further, this allows the physician to immediately test the implanted device during the surgical procedure. 
     Those skilled in the art will appreciate that other power-up and power-down techniques may be implemented. For example, the transition points may be dynamic points that are based on a number of factors including, for example, the rate of change of the energy of the power source  315 , namely the slope of the curves of FIGS. 7 and 8. Advantageously, this factor ensures that the current drain is not damaging the battery. Another factor that may be considered is the age of the battery. With an older the battery, the transition points may need to be varied. Another factor is the energy demands of the therapy. If the therapy has limited energy demands, then the first transition point may be occur at a later point in time. Further, additional transition points may be included. For example, there may be a point before T 1  (FIG. 7) where a warning signal may be provided to the patient before the treatment therapy is turned off. 
     In alternative embodiments, the power management system of the present invention can be used with any number of implantable systems requiring a self-contained power source, including, but not limited to, pacemakers, defibrillators, and cochlear implants. In another alternative embodiment, the power management system of the present invention may be used with implantable diagnostic devices for detecting bodily conditions of certain organs, like the brain or the heart. In yet another alternative embodiment, the power management system of the present invention can be used within a drug delivery system having an implantable battery-powered pump. The power source in any of the these embodiments may be rechargeable or non-rechargeable. If rechargeable, the power source may be a lithium ion battery. The power source may also be a capacitive power source or any other source. The present invention serves to manage the energy of any of these power sources and to efficiently allocate the energy during times of low energy. 
     Those skilled in that art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention, as defined in the accompanying claims. Thus, while various alterations and permutations of the invention are possible, the invention is to be limited only by the following claims and equivalents.