Patent Publication Number: US-2010130263-A1

Title: System and method for dual power source management

Description:
BACKGROUND 
     Mobile devices, such as mobile phones and media players, are prevalent in many aspects of a modern lifestyle. It is often the case that these devices are called upon to constantly function, i.e., to be constantly “on.” For example, a person&#39;s mobile phone may be required to be on at all times so that the person may be reached. As a result, the power source (e.g., a battery) required to provide power to the device needs to be long-lasting and easily replenished. 
     Typically, a mobile device, i.e., a device that can operate for an exact period of time without drawing power from an AC source, such as a wall outlet, will have one or more batteries to provide power. A battery provides a DC power source to the mobile device and has a life that is indirectly proportional to the current load drawn by the mobile device. As current is drawn from the battery, its charge is eventually depleted and, therefore, the battery must be recharged, typically by using a charging device that plugs into a power source, such as a wall outlet or automobile power outlet. The development of better batteries has led to longer battery life and shorter recharging time. 
     Nevertheless, there are many times that a mobile device will deplete its battery before one is able to get to a location where one can recharge the battery. Thus, a user of a mobile device may choose to carry a second battery or even have a mobile device that utilizes two batteries. This allows a user to remove and charge one battery while the other battery is used in the mobile device. Whether the user swaps batteries or manually switches in a second battery that is already installed in the mobile device, a number of problems may exist. 
     For example, if a user needs to swap one battery for another, the mobile device must be powered down in order to remove the deployed battery. (That is, as soon as the battery in operation is removed, the mobile device immediately ceases operation since it has no power source.) As a result, the mobile device is not operational during the battery swap. For a mobile device, such as a mobile phone that is the only means of communication for a user, any downtime required for battery change may be unacceptable. Furthermore, some mobile devices have security measures in place for sounding an alarm if an unauthorized person attempts to remove various parts (e.g., SIM card, memory card) of the mobile device. Thus, if the single battery is removed and all operations cease, the device may not be able to sound an alarm if an unauthorized person is trying to remove, e.g., the device&#39;s SIM card or memory card. 
     Mobile devices that employ dual batteries may have other problems. One problem with dual-battery devices is that the devices typically require an extra power-management integrated circuit (IC) having its own dedicated processor to manage both batteries. An extra IC takes up extra space and adds cost and power consumption to the mobile device. Furthermore, the use of the additional power management IC may require use of additional inputs and outputs from a main processing unit (e.g., a base band IC of a base band chip set (BBCS) thus preventing the use of these inputs and outputs for other purposes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of the subject matter disclosed herein will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of an embodiment of a dual power source management system. 
         FIG. 2  is a schematic diagram of an embodiment of a charge-control circuit that may be part of the dual power source management system of  FIG. 1 . 
         FIG. 3  is a schematic diagram of an embodiment of power selection circuit that may be part of a dual power source management system of  FIG. 1 . 
         FIG. 4  is a schematic diagram of an embodiment of power-source selection control circuit that may be part of the dual power source management system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is presented to enable a person skilled in the art to make and use the subject matter disclosed herein. The general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the subject matter disclosed herein. This disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein. 
       FIG. 1  is a block diagram of an embodiment of dual power source management system  100 . The system  100  may be disposed in a mobile device  103  such as a cell phone, and may form part of a power-management schema for the mobile device. Such a power-management schema may be implemented and controlled by a central processing unit (CPU) for the entire mobile device, often called the base-band integrated circuit (BBIC)  101 . The BBIC  101  may be one of multiple ICs in one package that may collectively be called a base-band chip set (BBCS). The BBIC  101  may include various General Purpose Input/Output Pins (GPIO) as well as various Analog-to-Digital converter Input pins (ADC). As with any IC, the number of these pins may be limited because of size and cost issues. 
     Although shown as a single line connection between the BBIC  101  and a battery-control circuit  102 , it is understood that several electronic connections may be encompassed within this graphical illustration. In an embodiment of the mobile device  103 , there are just three GPIO pin connections and two ADC pin connections between the BBIC  101  and the battery-control circuit  102  as described below in conjunction with  FIGS. 2-4 . Implementing a power-management schema with relatively few connections to the BBIC  101  may be an advantage over power-management schemas of the past because of the lower number of control connections. Furthermore, the battery-control circuit  102  may be smaller, less complex, and may consume less power than a dedicated power-management I. 
     The system  100  may typically include two batteries, a main battery  110  and an auxiliary battery  111 . The is no implied meaning from the name of these batteries to suggest that one is more powerful than the other or one that is in use more than the other. In fact, these batteries may be identical to each other in size, shape, and electrical characteristics. A suitable battery for use in the mobile device  103 , such as the batteries  110  and  111 , may be a conventional nickel-cadmium battery or a conventional lithium-ion battery. 
     Each battery may be connected to or disconnected from various circuits in the system  100 . A charge-control circuit  144  within the battery-control circuit  102  may be used to charge either the main battery  110  or the auxiliary battery  111  (when installed). When either battery  110  or  111  is coupled to the charge-control circuit  144 , the respective coupled battery may be charged by an external battery charger  122  such as from AC current drawn from a typical wall outlet or from any other power outlet (e.g., in a car, a plane). Similarly, a power-select circuit  154  may couple one or the other battery to a power-distribution circuit  170  which supplies power to the BBIC  101 , battery-control circuit  102  and other components of the mobile device  103 . The nature and operation of such couplings is described in greater detail below with respect to  FIGS. 2-4 . 
     In an embodiment, during operation, one of the batteries  110  and  111  may be coupled to the charge-control circuit  144  while the other battery is coupled to the power-distribution circuit  170 . However, there may be operational modes where both batteries are uncoupled from the charge-control circuit  144  (i.e., both batteries  110  and  111  are fully charged), both batteries  110  and  111  are uncoupled from the power distribution unit  170  (i.e., the mobile device  103  is powered by the battery charger  122 ), or both batteries  110  and  111  may be coupled to the battery charger  122  (wherein the battery charger  122  is acting as an AC-to-DC adapter). Various operations and modes for coupling batteries to these components are discussed in more detail below. 
       FIG. 2  is a schematic diagram of a charge-control circuit  144  that may be part of the dual power source management system  100  of  FIG. 1  according to an embodiment of the subject matter disclosed herein. In this circuit  144 , a determination is made as to which battery may be connected to the charge-control circuit  144  at a charge terminal  200 . The main battery (not shown in  FIG. 2 ) may be electrically connected at the main battery terminal  201 . Similarly, the auxiliary battery (not shown in  FIG. 2 ) may be electrically connected at the auxiliary battery terminal  202 . Other signals used to make this determination include a charge switch signal  223 , a current sense signal  222 , a battery charging signal  221  and a battery selection signal  220 , all of which are discussed further below. 
     The battery-selection signal  220  selects one battery or the other to couple to the charge signal  200 . The battery-selection signal  220  may be generated by the BBIC  101  at one of its GPIO pins. A system designer may program the BBIC  101  to select which battery to charge and when according to any criteria desired. As but one example, a designer may monitor an auxiliary battery sense signal and main battery sense signal (both shown in  FIG. 4  and discussed further below). Then, the BBIC  101  may determine which of the batteries exhibits a lower voltage sense signal and thereby select the lowest charged battery for charging. Other scenarios are contemplated as part of an overall power-management schema as discussed further below. 
     In an embodiment, the selection of using one battery over the other is determined by the logical value of the battery selection signal  220 . If the battery selection signal  220  is a logical high signal, then the transistor Q 4   211  and transistor Q 5   210  are turned on. In turn, the gates of each of the p-channels MOSFETS of switch  132  are pulled low via the transistor Q 4  and this closes the switch  132 . As a result, the auxiliary battery terminal  202  is coupled to the charge signal  200  such that the auxiliary battery  111  is charged. Therefore, if the charge switch signal  223  is a logical low signal, which is to say, an AC power is present (e.g., the mobile device is plugged into an external power source and senses a signal at the charge switch signal terminal  220 ), then the auxiliary battery  111  coupled to the auxiliary battery terminal  202  will begin receiving a charge from the charge signal  200 . Further, switch  130  remains open as the gates of the p-channel MOSFETS are driven high from the current through transistor  210 . This uncouples of the main battery  110  from the auxiliary battery  111  while the auxiliary battery  111  is being charged. The p-channel MOSFETS of the switch  130  have their bodies biased in such a way as to implement back-to-back connected body diodes that electrically isolate the main battery  110  from the auxiliary battery  111 . 
     In a similar but opposite manner, if the battery selection signal  220  is a logical low signal (e.g., 0 V), then the transistor Q 4   211  and transistor Q 5   210  are turned off. In turn, the gates of each of the p-channels MOSFETS of switch  130  are pulled low (via the ground path through resistor R 5 ) which closes s this switch  130 . As a result, the main battery terminal  201  is coupled to the charge signal  200 . Therefore, if the charge switch signal  223  is a logical low signal, then the main battery  110  coupled to the main battery terminal  201  will be charged via the charge signal  200 . Further, switch  132  remains open as the gates of the p-channel MOSFETS are pulled up from via the resistor R 6 . This uncouples the auxiliary  111  battery from the main battery  110  while the main battery  110  is being charged. Similar to above, the p-channel MOSFETS of the switch  132  have their bodies biased in such a way as to implement back-to-back connected body diodes that electrically isolate the main battery  110  from the auxiliary battery  111 . 
     The power-management schema embodied in the charge-control circuit  144  of  FIG. 2  may offer a number of advantages over conventional systems. As discussed above, the switches  130  and  132  are realized as p-channel MOSFETs with back-to-back body diodes. Such dual p-channel MOSFETs may be found in a FDMA1023PZ IC available from Fairchild Semiconductor™. Because of the back-to-back body diodes, when each p-channel MOSFET transistor is off, negligible or no reverse current from whichever of the main battery  110  or auxiliary battery  111  is uncoupled from the charge signal  200 . With any reverse current being rendered negligible, the main and auxiliary batteries  110  and  111  are sufficiently isolated to prevent any damage that may be caused if the batteries are coupled to each other. 
     In yet another potential advantage of the power-management schema described with respect to  FIG. 2 , automatic switching between utilizing and charging the main battery  110  or the auxiliary battery  111  may be realized. Furthermore, if an attempt at removing the main battery  110  in order to remove other components, such as a SIM card, the auxiliary battery  111  may still be engaged to execute security measures. 
       FIG. 3  is a schematic diagram of an embodiment of a power source selection circuit  300  for generating the voltage, LPWR  215  of  FIGS. 2 and 4  that may be part of a dual power source management system  100  of  FIG. 1 . This circuit  300  assures that LPWR  215  is generated from the highest of the three sources; the main battery  110 , the auxiliary battery  111  and the charge signal  200 . By being able to be generated by any of these three power sources, the circuit  144  (and circuit  154  of  FIG. 4 ) can operate if one of these sources is not present. 
       FIG. 4  is a schematic diagram of an embodiment of the power-source selection circuit  154  that may be part of the dual power source management system  100  of  FIG. 1 . The power-source selection circuit  154  monitors the voltage level of each battery (main  110  and auxiliary  111 ) and depending on which of the batteries is under load, may switch to the other if necessary. A resistor divider (comprising resistors R 14  and R 15 ) provides a main battery sense signal  401  and another resistor divider (comprising resistors R 12  and R 13 ) provides an auxiliary battery sense signal  402 . The main battery sense signal  401  and the auxiliary battery sense signal  402  are provided to the BBIC  101  via the two ADC pins used for the power-management schema for the dual power management system and used to determine which battery may need charging and which battery to use as the power source for the mobile device  103 . 
     As discussed above, the BBIC  101  utilizes various signals to determine a power management scheme. Thus, if it is determined that the main battery  110  will be used to power the mobile device, the BBIC  101  closes the switch  131  (to connect the main battery terminal  201  to the B+ voltage terminal  400 ) and opens the switch  133  (to disconnect the auxiliary battery terminal  202  from the B+ voltage terminal  400 ). Likewise, if the power-management schema determines that the auxiliary battery  111  will be used, the BBIC  101  closes switch  133  and opens switch  131 . The remaining circuitry of the power-source selection circuit  154  assures that the switching between batteries is fast and efficient. 
     The respective switches that engage or disengage the main and auxiliary batteries  110  and  111  are controlled by a signal from the output of a NAND gate  451 . Based upon the input to the NAND gate  451 , the resulting output signal will either be a logical high value or a logical low value. A logical high value at the NAND gate  451  output corresponds to engaging (for load) the main battery  110  and disengaging the auxiliary battery  111 , while a logical low signal at the NAND gate  451  output corresponds to engaging the auxiliary battery  111  and disengaging the main battery  110 . 
     In greater detail, if the NAND gate  451  output is a logical high signal, then the inverter  431  outputs a logical low signal. In turn, the gates of each of the p-channels MOSFETs of Q 7  (i.e., switch  131 ) are pulled low, which closes this switch  131 . As a result, the main battery terminal  201  is coupled to the B+ voltage terminal  400 . Further, with a logical high signal from the NAND gate  451 , a logical low signal emanates from the output of a coupled Schmitt trigger  420  (which also inverts the signal). This low logical signal causes the driver  433  to output a logical high signal and the switch  133  remains open as the gates of the p-channel MOSFETs of Q 6  (i.e., switch  133 ) are pulled high. This electrically isolates the auxiliary battery  111  from the B+ terminal  400  while the main battery  110  is being engaged to provide power to the B+ terminal  400 . 
     In a similar but opposite manner, if the NAND gate  451  output is a logical low signal, a logical high signal is output from the coupled Schmitt trigger  420 . Therefore, the driver  433  outputs a logical low signal. In turn, the gates of each of the p-channels MOSFETs of Q 6  (i.e., switch  133 ) are pulled low, which closes this switch  133 . As a result, the auxiliary battery terminal  202  is coupled to the B+ voltage terminal  400 . Further, the logical low signal from the output of the NAND gate  451  causes the driver  431  to output a logical high signal, which causes the switch  131  to remain open as the gates of the p-channel MOSFETs of Q 7  (i.e., switch  131 ) are pulled high. This electrically isolates the main battery  110  from the B+ terminal  400  while the auxiliary battery  111  is being engaged to provide power to the B+ terminal  400 . 
     The Schmitt trigger  420  assures that the leading edge of the logical high signal that turns on the switch  133  (i.e., Q 6 ) does so in a relatively fast manner. Thus, the Schmitt trigger  420  turns the switch  133  on fast enough to prevent power loss failure in the mobile device. Having such a Schmitt trigger  420  at this coupling provides fast switching (under 20 nanoseconds) when transitioning from having the main battery providing power to the B+ terminal  400  to having the auxiliary battery provide this power and vice versa. 
     The inputs of the NAND gate  451  are determined as part of the programmable power-management schema as described herein. A programmable GPIO pin from BBIC  410  may be used to provide logical high signals and logical low signals as part of the power-management schema and may be programmed by an end user accordingly. In one power-management schema, an end user may program a GPIO pin of BBIC  410  to control Q 11  for switching the power-source to auxiliary battery  111  when the main battery  110  voltage falls below a certain threshold. Thus, when the main battery sense signal  401  falls below the threshold, a logical high signal is output from the GPIO pin of BBIC  401 , so Q 11   411  is on and the Pin 1  of the NAND gate  451  is low. Any logical low signal at any input of the NAND gate  451  will cause its output to be a logical high value. As described above, a logical high signal at the output of the NAND gate  451  will open the switch  131  that engages the main battery  110  and close the switch  133  that engages the auxiliary battery  111 . So therefore, when the main battery  110  falls below the threshold, the power-management schema automatically switches in the auxiliary battery  111  within 20 nanoseconds of disconnecting from the main battery  110  and also assures that the main battery  110  is disengaged before the auxiliary battery  111  is engaged. Such a fast changing from one battery to the next assures that no lapse in operation of the mobile device  103  is experienced. Further, one may even perform a “hot swap” of one of the batteries, even if it is providing power to the B+ terminal  400  when removed. 
     As the auxiliary battery  111  is engaged, it is desired to not immediately switch back to the main battery  110 . Such switching back to the main battery  110  may occur if its sensed voltage rises above a threshold, which may be due to recharging the main battery or by removing the load (e.g., power supplied to the mobile device  103 ) from pulling its voltage lower. If there is no prevention of immediately switching back to the main battery  110 , a problem arises wherein switching back to loading the main battery  110  may occur rapidly and repeatedly. It may be advantageous to fully charge the main battery  110  before switching back again or to deplete the auxiliary battery  111  below its respective threshold before switching. Again, these options may be programmed by an end user according to a desired power-management schema. 
     As such the power-selection circuit  154  provides circuitry for the prevention of such rapid and repeated switching. The transistor Q 10   460  provides a battery switch pulse signal  471  to one of the GPIO pins of the BBIC  101 . When IC 1   450  outputs a logical low signal on pin  1 , the transistor Q 10   460  turns off which sends a battery switch pulse signal  471  to the BBIC  101 . The BBIC  101  senses this and, in response, outputs a logical high signal to another one of the GPIO pins  410  used. This pin provides an auxiliary battery lock-in signal  410  and is coupled to the input of a transistor Q 11   411 . This signal  410  will cause the transistor Q 11  to pull a logical low signal at a second input of the NAND gate  451 . Having a second logical low signal at an input to the NAND gate  451  prevents the circuit  154  immediately reengaging the main battery  110  even if pin  1  of IC 1   450  returns to a logical high signal in response to the voltage at the main battery  110  recharging to exceed a threshold to once again provide power to the B+ terminal  400 . 
     The power-management schema may be configured at the BBIC  101  to not remove the auxiliary lock-in signal  410  (i.e., switch from a logical high signal to a logical low signal) e.g., for a specific time period (e.g., three hours), until the mobile device  103  is plugged in to an external power source, or until the main battery  110  is sensed to be charged to full capacity. Further, the transistor Q 10   460 , in addition to providing a means for preventing rapid and repeated battery switching can also provide a notification signal that the main battery  110  has been discharged. Thus, the BBIC  101  may be configured to turn on an LED that indicates to a user that the main battery has been depleted. This may also indicate that when the mobile device  103  is plugged in for recharging, the user can be assured that the main battery  110  is receiving the charge first. 
     During startup, the power-source selection circuit  154  works in a similar manner. The IC 1   450  may be a voltage detector IC with high detector threshold accuracy and an ultra-low supply current. IC 1   450  may also have a series fixed voltage detector threshold, such that the end user may select one fixed detector threshold based on a system voltage threshold. When the mobile device  103  is first powered up, the voltage at the main battery  110  may be sensed via IC 1   450  first and if the main battery  110  voltage is below a respective threshold, the power-management schema may cause the auxiliary battery  111  to be engaged initially. Similar to above, the lack of a sufficiently high enough voltage initially at the main battery  110  causes the IC 1   450  to output a logical low signal on pin  1 . Just as if the main battery  110  had transitioned from a sufficient voltage to below a threshold voltage, the transistor Q 10   460  turns off, which sends a battery switch pulse signal  471  to the BBIC  101 . The BBIC  101  senses this and, in response, outputs a logical high signal to another one of the GPIO pins  410  used. This pin provides an auxiliary battery lock-in signal  410  and is coupled to the input of a transistor Q 11   411 . This signal  410  will cause the transistor Q 11  to pull a logical low signal at a second input of the NAND gate  451 . 
     Thus, even if the main battery  110  is below the voltage threshold, at a zero-charge level, or perhaps is not even installed, the power-management schema allows for the immediate engaging of the auxiliary battery  111 . This is accomplished because resistor R 22  pulls pin  1  of IC 1   450  to a logical low signal is input to the NAND gate  451 . As before, any logical low signal at the NAND gate  451  engages the auxiliary battery  111 . 
     While the subject matter discussed herein is susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. Furthermore, those skilled in the art will understand that various aspects described in less than all of the embodiments may, nevertheless, be present in any embodiment. It should be understood, however, that there is no intention to limit the subject matter to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the subject matter discussed herein.