Abstract:
This invention includes a power management method and apparatus for portable electronic devices, like cellular phones for example, to which accessories may be attached. These accessories include MP-3 players, personal digital assistants, and pagers. In a simple embodiment, a battery pack having a fuel gauge and power management controller measure an energy profile required by the host. From this profile the power management controller can determine when accessories are attached to the host by the amount of power being drawn. When the capacity of the cell is reduced below a predetermined threshold, the power management controller notifies the user that a limited amount of operational time remains and accessories should be turned off. In another embodiment, the power management controller automatically allocates power between the host and accessories once the predetermined threshold has been reached.

Description:
BACKGROUND  
         [0001]    1. Technical Field  
           [0002]    This invention relates generally to rechargeable batteries, and more particularly to smart battery systems with power allocation capabilities.  
           [0003]    2. Background Art  
           [0004]    Portable electronic devices are becoming as standard an accessory as a wallet or purse. People are carrying cellular phones, personal digital assistants (PDAs), pagers and the like in record numbers. For example, according to the Cellular Telecommunications Industry Association (CTIA), cellular telephone usage in the United States increased 27% between 1999 and 2000. As of December, 2000, there were over 109 million cellular subscribers in the United States alone.  
           [0005]    Cellular telephones require batteries for portability. As people talk more and more on cellular telephones, they require more and more energy from batteries. To compound this battery capacity issue, there is a trend in the electronic accessories business to converge devices. For instance, cellular telephones are converging with personal data assistants (PDAs), MPEG-1 Audio Layer 3 (MP3) players, and the like. By way of example, the StarTac™ series phone manufactured by Motorola can be purchased with a clip-on personal data assistant, which is capable of storing appointments, phone lists, and to-do reminders. Additionally, the Visor™ personal data assistant manufactured by Handspring has an expansion slot that allows it to become a cellular telephone. Many cellular telephones have clip-on MP3 players as well.  
           [0006]    All of these peripheral devices rely on the phone&#39;s battery for power. With increasing frequency, manufacturers of portable electronic devices are turning to lithium-ion (Li-ion) and lithium-polymer (Li-polymer) rechargeable batteries as the primary power source. These chemistries are advantageous in that they have a high energy density, which means that they offer large amounts of power per unit volume.  
           [0007]    The various devices and high-speed circuitry associated with convergent products often consume large amounts of power when operating. This has created an additional strain on an already overtaxed battery. Nothing is more frustrating than missing a casting call for a Broadway musical because your phone battery is dead. When your agent calls for that Broadway audition, you may be very angry with yourself for having listened to the long version of “Stairway to Heaven” on your clip-on MP3 player instead of having saved the last 10% of your battery for that one additional call.  
           [0008]    In an attempt to solve this problem, manufacturers have turned to voltage-sensing fuel gauges to try and inform the user as to how much battery power remains. A problem with lithium-based batteries is that it is hard to measure just how much power is left in them by sensing the voltage. When a primary battery discharges, like an alkaline battery for instance, the voltage drops proportionally with capacity. Thus if the working voltage has dropped by X %, the capacity has dropped in a corresponding amount. To find out how much capacity you have left, all you need to do is measure the voltage and compare it to the initial value.  
           [0009]    Lithium-based batteries, by contrast, have a relatively flat discharge characteristic. The voltage stays essentially constant until the battery is “dead”, when the voltage drops very quickly. For this reason, lithium based systems comprising fuel-gauges that measure voltage can have inaccuracies of 25% or more.  
           [0010]    A more sophisticated, accurate method involves the use of a “Coulomb counter” fuel gauge. This fuel gauge measures the amount of power that has discharged from the battery by integrating current across time (Coulombs of charge). This technique can yield accuracy&#39;s of 1% or better in certain applications. The problem with Coulomb counting fuel gauges is that small portable products, e.g. phones, PDAs, and the like, do not have computing power available to perform power management functions in addition to measuring battery capacity.  
           [0011]    There is thus a need for an improved means of managing power in portable electronic devices. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 illustrates one embodiment of the invention having a minimal set of features in accordance with the invention.  
         [0013]    [0013]FIG. 2 illustrates an alternative embodiment having a minimal set of features in accordance with the invention.  
         [0014]    [0014]FIG. 3 is a schematic diagram of a preferred embodiment of the invention.  
         [0015]    [0015]FIG. 4 is an exemplary flow chart of a preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a”,“an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” 
         [0017]    In one preferred embodiment, this invention includes a simple power management scheme for allocation of energy from a Li-ion power source to portable device accessories using a coulomb counting energy measurement technique.  
         [0018]    This invention supplies power to peripheral devices while minimizing the overall power drain from the battery. The invention also reserves a minimum amount of operating power for the primary portable device, known as the host, by shutting down peripheral devices. Moreover, this invention offers simplicity of implementation with minimal impact on host or accessory devices. The invention resides primarily with the energy source, as the energy source for these products is typically removable and separate from the remaining system. The advantage of a battery resident energy management function is to allow the simpler host design and to allow the user a choice in optional features.  
         [0019]    In its simplest form, the invention comprises a firmware algorithm that resides in the host processor and associated memory. The host processor receives power management data from a power management controller in the battery. Upon receiving this data, the host processor actuates a firmware algorithm to determine whether to alert the user to an excessive battery drain condition.  
         [0020]    Referring now to FIG. 1, illustrated therein is a block diagram of a hardware system  100  in accordance with a minimal feature set embodiment of the invention. The central component of the system  100  is the host device  103 , which may be a cellular telephone, two-way radio, pager, PDA or similar portable electronic device. The host device  103  includes a host processor  104  that executes the device&#39;s firmware code, operating system and corresponding algorithms. One example of such a processor is the MC9328MX1, manufactured by Motorola.  
         [0021]    Attached to the host device  103  is a battery  105  having a rechargeable cell  109 , a fuel gauge  107 , a current sense circuit  108  and a power management controller  106 . The fuel gauge  107  measures the amount of charge entering and leaving the cell  109  as is known in the art. One example of such a fuel gauge is the bq2060 manufactured by Benchmark, a subsidiary of Texas Instruments. The fuel gauge  107  may use one of several techniques to sense current, including employing a current sense resistor  108 . When current flows through the current sense resistor  108  a voltage is created across the resistor. By sensing this voltage across time, in addition to sensing the voltage of the cell  109 , the fuel gauge  107  is able to measure the power flowing into and out of the cell  109 .  
         [0022]    The power management controller  106  assimilates various battery data and transports it to the host processor  104  across a data bus  110 . This data bus  110  may be as simple as a one-wire interface. Such interfaces are used by power management controllers like the DS2438 manufactured by Dallas Semiconductor. Typical battery data includes cell capacity, cell state of charge, cell voltage, temperature, charging status, time, pressure and the like. Additional information maintained by the power management controller includes date of manufacture, service date, number of cycles used, preferred charging instructions and other cell specific data.  
         [0023]    The host also includes at least one accessory device  101 . The accessory device  101  may be a PDA, MP3 player, or other accessory. In any event, presuming that the accessory device  101  is electronic, it will act as a load on the battery  105 . For simplicity, the loading is shown here as a resistor  102 , as loads accessories  101  often draw continuous average current.  
         [0024]    In the simplest embodiment, the battery power management controller  106  has stored within data relating to the maximum and typical host  103  power consumption requirements. This information may reside in host processor  104  as well. This data can be programmed either at the time of manufacture or in the field through real-time measurement and calibration during the charging and discharging cycles.  
         [0025]    As the power management processor  104  has the data relating to the typical power consumption requirements of the host  103 , the power management controller  106  may define a typical energy usage profile for the host  103 . The energy usage profile may include a predetermined threshold. For example, if the energy usage profile is such that the host  103  typically requires 4 watts to operate, and the cell  109  can hold a maximum of 27 k Joules, the threshold may be set at 7 k Joules, which corresponds to {fraction (1/2)} hour of remaining host  105  life.  
         [0026]    If at some point the typical usage profile is exceeded by a predetermined amount, the total load is 6 watts as opposed to 4 watts for example, then the power management processor  106  is alerted that the additional energy demand is due to one or more accessory products. Once the predetermined energy threshold is reached, the power management controller  106  communicates to the host processor  104  that the cell  109  is becoming depleted. The host  103  will then inform the user of this condition, thereby allowing the user to turn off the accessory  101 .  
         [0027]    Referring now to FIG. 2, illustrated therein is alternative embodiment having a minimal set of features in accordance with the invention. The circuit in FIG. 2 includes the same components as that shown in FIG. 1, but also includes a pass transistor  111 . The host processor  104  controls the pass transistor  111  via the control line  112 .  
         [0028]    In this embodiment  200 , in addition to alerting the user, the host processor  104  is able to actuate the pass transistor  111 , thereby opening the circuit between battery cell  109  and load  102 . When the pass transistor  111  is opened, the accessory  101  is no longer coupled to the battery  105 . The accessory  101  thus stops drawing power, thereby conserving power for the host. The host processor  104  performs this actuation function when the predetermined energy threshold is reached.  
         [0029]    The primary advantage of the embodiments shown in FIG. 1 and FIG. 2 is that prior art systems may be retrofitted with the invention with only a firmware code change. No new hardware is needed. It will be clear to those skilled in the art that the embodiments of FIG. 1 and FIG. 2 could be extended to a plurality of accessories coupled to a single host.  
         [0030]    Referring now to FIG. 3, illustrated therein is a preferred embodiment of the invention. This embodiment employs a simple accessory modification that allows the battery  305  to directly control power to each accessory device  301 ,  321 ,  331 . A coulomb counting fuel gauge  307  measures remaining capacity in the cell(s)  309 . This value is compared against predetermined thresholds for the host  303 .  
         [0031]    Each accessory  301 ,  321 ,  331  coupled to the host  303  communicates its power requirement to the power management controller  305 . In one exemplary embodiment, this is achieved with pull down, or “power demand”, resistors  344 ,  345 ,  346 . The power management controller  306  senses the voltage of the power requested terminal  348  with an on-board A/D converter. The value of this voltage is determined by the value of the pull-up resistor  349  and the paralleled impedances of the power demand resistors  344 ,  345 ,  346 . In this embodiment  300 , the lower the voltage of the power requested terminal  348 —corresponding to more parallel power demand resistors—the more power the accessories  301 ,  321 ,  331  will consume. It will be clear to those skilled in the art that other more elaborate power demand identification schemes may be utilized with similar effects.  
         [0032]    The power management controller  306  continually monitors the power demanded and the remaining cell  309  capacity. When the capacity drops below a predetermined threshold, the power management processor  306  can alert the user or, in the alternative, deactivate the accessories by toggling the power enable line  347 . In this exemplary embodiment  300 , when the power enable line  347  is toggled, the pass transistors  341 ,  342 ,  343  open, causing the accessories  301 ,  321 ,  331  to deactivate.  
         [0033]    Referring now to FIG. 4, illustrated therein is a flow chart of a preferred embodiment of the invention. This flow chart is one example of a firmware algorithm that is programmed into either a power management controller or host processor. Those of ordinary skill in the art of programming will recognize steps  401  and  402  as initialization steps. Beginning at step  401 , the battery cell is initiated to supply power to the host. This is the normal mode of operation. Additionally, in step  402 , the power connections to accessory connectors are initialized to deny power to accessories. From these initialization points, we are ready to enter the routine.  
         [0034]    At step  403 , the power management controller takes a snap-shot of the battery conditions by reading the fuel gauge. The power management controller is thus able to determine capacity remaining in the cell. The power management controller may also check other parameters including rate of discharge or charge.  
         [0035]    Step  404  is where the user attaches an accessory to the host device. Immediately thereafter, power management controller determines the total power requested  405 . This may be done in any of a number of methods, including the resistors of FIG. 3, multiple inputs to a summing amplifier from each accessory, or digital information implemented across a communications bus.  
         [0036]    Once the total power demand has been determined, decision  406  checks to see whether the user has enabled the automatic power allocation. If the automatic power allocation has been activated, the power management controller will disable accessories automatically via means like the pass transistors of FIG. 3 or other equivalents when the predetermined threshold has been met. The power management controller will additionally notify the user of the power management activity and of low energy warnings. This is represented by the branch of the flow chart beginning with step  407 .  
         [0037]    If automatic power allocation has either not been selected or has been disabled, the power management controller will notify the user that the predetermined threshold has been met without automatically disabling accessories. This is analogous to the embodiment of FIG. 1. This is represented on the flow chart by the loop beginning at step  409 .  
         [0038]    The present invention offers numerous advantages over the prior art. No databases are required to log information about each accessory. This invention tracks the total amount of power available from the cell and the total amount requested from all devices. Additionally, no device priorities are required. With the exception of the host, all other attached devices are identical in priority. This invention is wholly or primarily contained with the energy source, whereas other prior art solutions were completely contained in the host.  
         [0039]    Another advantage is that this invention is separate and independent of battery charging systems, and does not involve voltage outputs or feedback for linear regulation. This invention does not involve having the battery or host revert to an alternate power operating mode, e.g. sleep or suspend in response to an external device connection. The connection of an external accessory for this invention will simply result in power being made available—or not—to operate the accessory. The invention will not arbitrate among devices to shut some down or cause the host or battery to enter a suspend state. This invention does not require or necessarily involve the use of memory.  
         [0040]    While the preferred embodiments of the invention have been illustrated and described, it is clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the following claims.