Abstract:
A power management circuit for a battery operated electrical device that may include a number of switching circuits. The switching circuits are coupled between the battery and a corresponding one of various electronic sub-circuits. A battery monitoring circuit is arranged to monitor a voltage associated with the battery. Each switching circuit selectively couples a corresponding one of the electronic sub-circuits to the battery based on the battery voltage. In another example, the monitor circuit and the switching circuit functions are provided within the corresponding electronic sub-circuit. Battery power is conserved by selectively disabling (i.e., placing them in a sleep mode) the various electronic sub-circuits based on the battery voltage. The power management circuit may be arranged to select between charger circuits that have distinct charging characteristics, as well as to enable/disable various analog and digital electronics in the battery operated electrical device depending upon the monitored battery condition.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to power management in a battery powered electronic system. More specifically, the present invention is related to a power management system that is employed by a portable electronic system by selectively placing various electronic sub-circuits within the portable electronic system into a sleep mode based on the battery voltage. 
     BACKGROUND OF THE INVENTION 
     Many portable electrical devices utilize a rechargeable battery to provide power to the electrical devices. These devices include computers, cellular telephones, pagers, radios, power tools, and the like. For improved service life and extended time between charges, these batteries and devices often include a control circuit (commonly called a power controller, a battery control circuit, a charge controller, and the like) to control the charging and/or the discharging of the battery. The control circuit controls the battery charge by a charger circuit, and controls the discharge of the battery by deactivating control circuit units to prevent drainage of the battery unit. 
     A battery charge circuit having a given charge characteristic may be most appropriate for charging a battery based on various criteria such as battery type, and charge storage capacity. For example, Lithium-Ion batteries and Lithium-Polymer batteries are often used in portable applications such as cellular telephones. Lithium batteries are sensitive to excessive voltages, which may result in damage to the battery and/or a possibly explosive condition. The battery charger and controller design for a Lithium-Ion battery should include a suitable safety circuit (i.e., a shunt regulator) to prevent overcharging the battery. 
     SUMMARY OF THE INVENTION 
     The present invention is directed at a power management circuit for a battery operated electrical device that may include a number of switching circuits. The switching circuits are coupled between the battery and a corresponding one of various electronic sub-circuits. A battery monitoring circuit is arranged to monitor a voltage associated with the battery. Each switching circuit selectively couples a corresponding one of the electronic sub-circuits to the battery based on the battery voltage. In another example, the monitor circuit and the switching circuit functions are provided within the corresponding electronic sub-circuit. Battery power is conserved by selectively disabling (i.e., placing them in a sleep mode) the various electronic sub-circuits based on the battery voltage. The power management circuit may be arranged to select between charger circuits that have distinct charging characteristics, as well as to enable/disable various analog and digital electronics in the battery operated electrical device depending upon the monitored battery condition. 
    
    
     A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detailed description of illustrative embodiments of the invention, and to the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an exemplary control circuit; 
     FIG. 2 is a state diagram for an exemplary control circuit; 
     FIG. 3 is another state diagram for an exemplary control circuit; and 
     FIG. 4 is a schematic diagram of a portion of an exemplary control circuit, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before exemplary embodiments of the present invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced or being carried out in various ways. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and other changes may be made, without departing from the present invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     Throughout the specification, and in the claims, the term “connected” means a direct electrical connection between the things that are connected, without any intermediary devices. The term “coupled” means either a direct electrical connection between the things that are connected, or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means one or more passive and/or active components that are arranged to cooperate with one another to provide a desired function. The term “signal” means at least one current signal, voltage signal or data signal. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on”. Also, “battery” includes single cell batteries and multiple cell batteries. 
     FIG. 1 is a schematic diagram of an exemplary battery-powered system ( 100 ) that includes power management, in accordance with the present invention. The exemplary battery-powered system ( 100 ) includes a first charger circuit ( 110 ), a second charger circuit ( 120 ), a protection circuit ( 130 ), a digital circuit ( 140 ), an analog circuit ( 150 ), a monitor circuit ( 160 ), five switching circuits (SC 11 -SC 15 ), a rechargeable battery (CELL), and a load circuit (LOAD). The power management system may be implemented, in whole or in part, as an integrated circuit. Moreover, the battery-powered system may be integrated, in whole or in part, into a single system that includes the power management system. The rechargeable battery may be any type of rechargeable battery such as nickel-cadmium, nickel-metal-hydride, lithium-ion, and lithium-polymer. 
     Monitor circuit  160  is arranged to sense the voltage (VCELL) of the rechargeable battery and provide control signals (POR 1 -POR 5 ) based on the sensed voltage. Charger circuit  110  is arranged to couple power from an input power source to rechargeable battery CELL when switching circuit SC 12  is in a first position. Charger circuit  120  is arranged to couple power from an input power source (VIN) to the rechargeable battery CELL when switching circuit SC 12  is in a second position. Switching circuit SC 12  is selectively switched between the first and second positions in response to control signal POR 2 . Protection circuit  130  is coupled to input power source (VIN), and selectively coupled to rechargeable battery CELL through switching circuit SC 11 , when switching circuit SC 11  is actuated by control signal POR 1 . The load circuit (LOAD) is selectively coupled to rechargeable battery CELL though switching circuit SC 13 , when switching circuit SC 13  is actuated by control signal POR 3 . Analog circuit  140  is selectively coupled to rechargeable battery CELL through switching circuit SC 14 , when switching circuit SC 14  is actuated by control signal POR 4 . Digital circuit  150  is selectively coupled to rechargeable battery CELL through switching circuit SC 15 , when switching circuit SC 15  is actuated by control signal POR 5 . 
     The sense voltage (VCELL) corresponds to the charge level of the rechargeable battery (CELL). The monitor circuit determines an operating range for the sense voltage, where each operating range corresponds to a range of voltages. Thus, the charge level of the rechargeable battery (CELL) corresponds to one of the operating ranges. The boundaries for the voltage ranges are determined by the battery type and any necessary requirements for the system (i.e., system  100 ). Each operating range corresponds to a different operating state for the system. 
     The monitor circuit is arranged to continuously monitor the sense voltage (VCELL). The monitor circuit ( 160 ) provides the control signals (POR 1 -POR 5 ) in response to the sense voltage (VCELL). The monitor circuit ( 160 ) quantifies the sense voltage to determine a current operating range for the rechargeable battery (CELL). Any number of ranges, and corresponding operating states may be employed as is necessary for a particular system implementation. 
     In one embodiment, the monitor circuit includes one or more comparator circuits that are arranged to compare the sense voltage (VCELL) to one or more corresponding reference voltages. The corresponding reference voltages are different from one another such that multiple operating states are determined for the system. For example, each circuit that is loading down the rechargeable battery (i.e., ANALOG CIRCUIT  140 , LOAD, and DIGITAL CIRCUIT  150 ) may be disabled when the rechargeable battery is below a first voltage level. By selectively disabling circuitry, power is conserved while the rechargeable battery has a low charge, and battery charging is facilitated with minimum loading. 
     Analog circuit  150  may be any analog circuit that is necessary in the system. Example circuits include current limiters, thermal sensors, voltage controllers as well as other analog circuitry. In one particular example, a band-gap reference circuit may be included in analog circuit  150 . The band-gap reference circuit may not provide a stable output voltage until the power supply for the band-gap reaches a minimum voltage level. The voltage monitor circuit asserts control signal POR 4  such that the analog circuit is decoupled from power (i.e., the rechargeable battery). By decoupling the analog circuit from power, the power supply (VS) for the band-gap reference circuit is disabled until the minimum voltage level for control signal POR 4  is achieved. 
     Digital circuit  150  includes any electronics that provide digital electronic functions. Example digital electronics include circuit components that are required to retain a state, such as, memory elements, state machines for charging/discharging algorithm execution, timers, data converters, and digital status drivers, as well as others. Similar to the analog circuits described above, the digital electronics may have a minimum safe operating range. By decoupling the digital circuit from power, the power supply (VS) for the digital circuit is disabled until the minimum voltage level for control signal POR 5  is achieved. 
     Although FIG. 1 illustrates two charger circuits, a single charger circuit, or a multiplicity of charger circuits may be employed as may be desired. One of the charger circuits ( 110  and  120 ) provides a charge path from the input power (VIN) to the rechargeable battery based on the sense voltage (VCELL). In one example, charger circuit  110  is arranged to operate when the sense voltage is below a minimum level (i.e a low voltage charger), and charger circuit  120  is arranged to operate when the sense voltage is above the minimum level (i.e., a high voltage charger). A charge path is selected based on the position of switching circuit SC 12 , which is responsive to control signal POR 2 . 
     Multiple charger circuits may be necessary in a system where a particular charger circuit may be unable to operate below a minimum. For example, a shunt regulator may have a minimum operating voltage of 2V for proper regulation. In this instance, the shunt regulator is coupled to the rechargeable battery when the sense voltage is above 2V, and a “trickle charge” circuit is coupled to the rechargeable battery when the sense voltage is below 2V. The trickle charge circuit may be a simple passive network, a diode circuit, or some other circuit that is arranged to provide a small charge to the rechargeable battery. 
     Protection circuit  130  is a circuit that is arranged to limit the input power (VIN) from damaging the electronic system ( 100 ), when activated. The protection circuit may be included in a shunt regulator circuit. In one example the protection circuit is arranged to operate as a crowbar circuit when activated. The protection circuit ( 130 ) is activated when switching circuit SC 11  is actuated in response to control signal POR 1 . By decoupling the protection circuit from the rechargeable battery, the power supply (VS) for the protection circuit is disabled until the minimum voltage level for control signal POR 1  (i.e., the minimum voltage level of the rechargeable battery is achieved such that POR 1  is asserted) is achieved. 
     A non-compliant power source corresponds to a power source that has a voltage and/or current characteristic that exceeds the design criteria for a rechargeable battery system. The use of a non-compliant charger in a charger system may result in an overcharged cell, or damage to the rechargeable battery system. Protection circuit  130  may also be arranged to protect electronic system  130  from damaging electronic system  100 . 
     The switching circuits (SC 11 -SC 15 ) each include a closed position and an open position. Each switching circuit is actuated in response to a respective controls signal (i.e., POR 1 -POR 5 ). In one example, one or more of the switching circuits are arranged to operate as voltage controlled switches that are in an open position when the control signal is above a switching voltage level, and in a closed position when the control signal is below the switching voltage level. In another example, one or more of the switching circuits are arranged to operate as voltage controlled switches that are in an open position when the control signal is above a first switching voltage level, and in a closed position when the control signal is below a second switching voltage level such that the switching circuit operates as a switch with hysteresis. The hysteresis may be employed to account for a power supply voltage (the sense voltage, VCELL) drop that is incurred while the rechargeable battery unit is loaded down by the various circuits. For example, the sense voltage (VCELL) is higher for an unloaded rechargeable battery than a loaded rechargeable battery. 
     The load circuit is a battery power consuming circuit. Example load circuits include a computer device, a cordless telephone, a pager, a cellular telephone, a handheld transceiver (i.e., walkie-talkie), a portable global positioning system (GPS) receiver, a power tool, and other devices that utilize a rechargeable battery. The load circuit is coupled to the rechargeable battery when switching circuit SC 13  is actuated by control signal POR 3 . By decoupling the load circuit from the rechargeable battery, the load circuit is effectively disabled and power is conserved. 
     The system employed by the present invention is arranged to sense the voltage of the rechargeable battery and selectively enable various circuits (i.e., circuits  110 - 150  and LOAD) using a monitor circuit ( 160 ) and associated switching circuits (i.e., SC 11 -SC 15 ). One or more general-purpose devices such as an analog-to-digital converter that is interfaced with digital logic, a microcontroller, and/or a processor may be arranged to perform the monitor circuit function. For example, an analog-to-digital converter may be employed to convert the rechargeable battery voltage to a digital representation, where a processor compares the digital representations to predetermined values. The predetermined values may be found, for example, in a look-up table, or a register or memory of the processor. The switching circuits (SC 11 -SC 15 ) may be replaced with another enable logic. The processor may also be responsive to a stored program that provides the functions of the monitor circuit and effectuates the activation of the various circuits as is desired. 
     The system employed by the present invention may be arranged to have a different sequence for discharging and charging of the battery cell. For example, the POR control signals are activated and deactivated based on different criteria when the rechargeable battery is discharging them when the rechargeable battery is charging. The POR signals have two operating modes: a sleep mode, and a wake mode. The sleep mode refers to the situation where various POR control signals become disabled during discharge, while the wake mode refers to the situation where various POR control signals become active while the rechargeable battery is charging. FIGS. 2 and 3 illustrate exemplary state diagrams of control signals POR 1 -POR 5  for the control system of FIG.  1 . 
     Control signal POR 1  transitions from active to sleep mode when the sense voltage (VCELL) is less than a first predetermined voltage level (V 101 ). POR 1  transitions from sleep mode to active mode when the charger is detected OR when the sense voltage (VCELL) exceeds a second predetermined level (V 102 ). In one example, V 102 &gt;V 101  such that the activation of switching circuit SC 11  has hysteresis. In another example, V 101 =V 102 . 
     Control signal POR 2  transitions from active to sleep mode when the sense voltage (VCELL) is less than a third predetermined voltage level (V 203 ). POR 2  transitions from sleep mode to active mode when the sense voltage (VCELL) exceeds fourth predetermined level (V 204 ). In one example, V 204 &gt;V 203  such that the activation of switching circuit SC 12  has hysteresis. In another example, V 204 =V 203 . 
     Control signal POR 3  transitions from active to sleep mode when the sense voltage (VCELL) is less than a fifth voltage level (V 305 ). POR 3  transitions from sleep mode to active mode when the sense voltage (VCELL) exceeds a sixth predetermined level (V 306 ). In one example, V 306 &gt;V 305  such that the activation of switching circuit SC 13  has hysteresis. In another example, V 306 =V 305 . 
     Control signal POR 4  transitions from active to sleep mode when the sense voltage (VCELL) is less than an eighth predetermined voltage level (V 408 ), or when a storage mode (STORAGE SLEEP) is activated. POR 4  transitions from sleep mode to active mode when the charger is detected or the sense voltage (VCELL) exceeds a tenth predetermined voltage level (V 410 ). A timer is started (START TIMER) when the sense voltage (VCELL) is less than a seventh predetermined voltage level (V 407 ). The timer is reset (RESET TIMER) when the sense voltage (VCELL) exceeds a ninth predetermined voltage (V 409 ) and the timer reaches a timeout condition (TIMEOUT). Control signal POR 4  returns to an active mode when the timer is reset. Control signal POR 4  transitions into the sleep mode when the sense voltage is below the ninth predetermined voltage (V 409 ) and the timer fails to reach the timeout condition (NO TIMEOUT). In one example, V 410 &gt;V 409 &gt;V 407 &gt;V 408 , such that the activation of switching circuit SC 14  has hysteresis. In another example, V 407 =V 409 , and V 108 =V 110 . 
     The storage mode may be activated by a digital control signal (not shown). The storage mode is useful for reducing power consumption when a particular system is implemented in a portable device that may be stored for a prolonged period of time without use. For example, a cellular telephone may be stored in a warehouse before sale for an extended period of time. In this instance, the cellular telephone is placed in a storage mode until activated by a user (i.e., after a sale). 
     Control signal POR 5  transitions from active to sleep mode when the sense voltage (VCELL) is less than a eleventh predetermined voltage level (V 511 ). POR 5  transitions from sleep mode to active mode when the sense voltage (VCELL) exceeds a twelfth predetermined level (V 512 ). In one example, V 512 &gt;V 511  such that the activation of switching circuit SC 15  has hysteresis. In another example, V 512 =V 511 . 
     In one embodiment of the invention, a common circuit such as the monitor circuit illustrated in FIG. 1 does not necessarily generate all of the control signals (POR 1 -POR 5 ). One or more of the circuits may be self-sensing such that a switching circuit and a monitor is unnecessary. For example, the protection circuit may include a resistor in series with the rechargeable battery such that one or more portions of the protection circuit are deactivated. The resistor may be arranged to provide a turn off path for one or more transistors in the protection circuit. In this instance, the protection circuit is disabled until the rechargeable battery reaches a sufficiently high voltage to activate the transistors in the protection circuit. Thus, it is within the scope of the present invention that each of the circuits ( 110 - 160 ) may be self-enabled by sensing the power supply (VCELL) directly. 
     FIG. 4 is a schematic diagram of another exemplary system ( 400 ) that includes sleep mode power management in accordance with the present invention. The exemplary system ( 400 ) includes a protection circuit ( 430 ), and a rechargeable battery (CELL). The sleep mode power management system may be implemented, in part or whole, as an integrated circuit. The rechargeable battery may be any type of rechargeable battery such as nickel-cadmium, nickel-metal-hydride, lithium-ion, and lithium-polymer. 
     Protection circuit  430  includes at least a first portion ( 432 ) and a second portion ( 434 ). The first and second portions are in communication with one another. For example, the first portion of the protection circuit may be activated by an enable signal (EN) that is provided from the second portion of the protection circuit. In this example, the second portion of the protection circuit is arranged to sense the voltage (VCELL) associated with the rechargeable battery (CELL), provide an enable signal when the sense voltage exceeds a predetermined level. As previously discussed with reference to FIG. 1, protection circuit  130  may be configured to operate without the necessity of a switching circuit (SC 11 ) and a monitor circuit ( 160 ). As shown in FIG. 4, protection circuit  430  is coupled to the rechargeable battery without the need of a monitor circuit (i.e., monitor circuit  160 ) and also without the need of a switching circuit (i.e. switching circuit SC 11 ). Instead, the second portion of the protection circuit is configured to operate as a voltage sense circuit that is employed to enable the first portion of the protection circuit. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.