Abstract:
In accordance with the teachings described herein, a method and apparatus for handling a charging state in a mobile electronic device is provided. A universal serial bus (USB) interface may be used for connecting the mobile device to a USB host. A processing device may be used to control operation of the mobile device and receive an enumeration acknowledgement signal from the USB host via the USB interface and generate an enable signal upon receiving the enumeration acknowledgement signal. The method and apparatus may further include a rechargeable battery, a battery charger, a timing circuit, and a battery charger enabling circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This continuation application claims priority from U.S. patent application Ser. No. 11/026,443, filed Dec. 30, 2004 by Martin G. A. Guthrie, et al, entitled “Method and Apparatus for Handling a Charging State in a Mobile Electronic Device” (10978-US-PAT1-4214-00704) and U.S. Provisional Application No. 60/545,434, filed Feb. 17, 2004 by Martin G. A. Guthrie, et al, entitled “Method and Apparatus for Handling a Charging State in a Mobile Electronic Device” (10978-US-PRV), which are incorporated by reference herein as if reproduced in their entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to mobile electronic devices. More particularly, the present invention relates to a method and apparatus for handling a charging state in a mobile electronic device. 
         [0003]    Portable systems, such as mobile electronic devices, which are powered by rechargeable batteries have a problem supporting both USB (Universal Serial Bus) charging state and suspend state functions. 
         [0004]    When a rechargeable battery is dead or not present, the mobile electronic device can not operate since it does not have any power. In order for the mobile electronic device to operate, the mobile electronic device is connected to a USB host in order to draw power from the host to both power up the device and recharge the battery. However, when the mobile electronic device is connected to the USB host, herein referred to as “VBUS detection, USB specifications require that the device initiate enumeration within 100 msec. Enumeration is the process whereby the device requests permission from the USB host to access the host. In this case, the enumeration request is directed to a request for the mobile electronic device to draw a current/voltage from the USB host in order to power up the mobile electronic device as well as to recharge the dead or non-present battery. 
         [0005]    In most cases, it is desired that a battery charger within the mobile electronic device turn on once it receives power from the USB host upon VBUS detection. This causes the battery charger to be enabled so that the current/voltage supplied by the USB host is used for operation of the device and recharging of the battery. This may be referred to as a device charging state. Therefore, when the voltage via the VBUS is applied, the battery charger is enabled and acts as a power source to power up the mobile electronic device and to recharge the battery. 
         [0006]    Another common state for the mobile electronic device is a device suspend state. USB specifications require that the total current supplied by the USB host to the mobile electronic device does not exceed 500 μA in the device suspend state. With many mobile electronic devices, 500 μA is not enough current for the processor or CPU in the mobile electronic device to operate and therefore the device is generally powered down. Powering down of the CPU in the mobile electronic device causes all the control signals to default to a low state signal, which causes the battery charger to be enabled. However, since 500 μA is not enough current for operation of the device, it is not desirable for the battery charger to be enabled during the device suspend state. In some other prior art devices, support for the device suspend state is not recognized and the battery charger remains enabled during the device suspend state. In this manner, the 500 μA current limit is not recognized or acknowledged by the mobile electronic device even though it is required by USB specifications. 
         [0007]    Furthermore, in some prior art devices, two separate signals to control the device charging state and the device suspend state are used. 
         [0008]    It is, therefore, desirable to provide a method and apparatus for handling a charging state and a device suspend state in a mobile electronic device. 
       SUMMARY 
       [0009]    In accordance with the teachings described herein, a method and apparatus for handling a charging state in a mobile electronic device is provided. A universal serial bus (USB) interface may be used for connecting the mobile device to a USB host. A processing device may be used to execute programs and to control operation of the mobile device. The processing device may be operable to receive an enumeration acknowledgement signal from the USB host via the USB interface and generate an enable signal upon receiving the enumeration acknowledgement signal. A rechargeable battery may be used to power the processing device. A battery charger may be used to receive a USB bus voltage from the USB interface and use the USB bus voltage to power the processing device and to charge the rechargeable battery. The battery charger may be further operable to receive a charge enable signal that enables and disables the battery charger from powering the processing device and charging the rechargeable battery. A timing circuit may be used to detect the USB bus voltage and to measure the passage of a pre-determined amount of time upon detecting the USB bus voltage. A battery charger enabling circuit may be used to generate the charge enable signal to control the battery charger, the battery charger enabling the battery charger if the timer has measured the passage of the pre-determined amount of time or the enable signal is received from the processing device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
           [0011]      FIG. 1  is a schematic diagram of a mobile electronic device connected to a Universal Serial Bus (USB) host. 
           [0012]      FIG. 2   a  is a schematic diagram of apparatus for handling a device charging state for a mobile electronic device. 
           [0013]      FIG. 2   b  is a schematic diagram of a second embodiment of apparatus for handling a device charging state for a mobile electronic device. 
           [0014]      FIG. 2   c  is a schematic diagram of a third embodiment of apparatus for handling a device charging state for a mobile electronic device. 
           [0015]      FIG. 3  is a flow diagram outlining a method of handling a device charging state for a mobile electronic device. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  is a schematic diagram of a mobile electronic device  10  connected to a Universal Serial Bus (USB) host  22 . The mobile electronic device  10  includes a central processing unit (CPU)  12  that is coupled to a charger interface  14  which, in turn, is coupled to a rechargeable battery  16 . The CPU  12  is also connected to the rechargeable battery  16  and to a USB interface  18  which is connected to a USB port  20 . In addition, the charger interface  14  is connected to the USB interface  18 . 
         [0017]    The USB interface  18  interacts with the USB port  20  to receive data and power from and transmit data to the USB host  22 . 
         [0018]    During operation of the mobile electronic device  10 , when a user determines that the rechargeable battery  16  is dead or not present, the user connects the mobile electronic device  10  to the USB host  22  via a USB cable  24 . Within the USB cable  24  are four separate circuit lines: a power line, a ground line and two data lines. At the USB host  22 , the USB cable  24  is connected to a USB host port  26 . A device interface  28  is connected to the USB host port  26  for transmitting data and power to and receiving data from the mobile electronic device  10 . The USB host  22  further includes a power source  30  and a USB host CPU  32  which are both connected to the device interface  28 . The power source  30  provides the requested power, in the form of a current/voltage, to the mobile electronic device while the USB host CPU  32  acknowledges enumeration and transmits a device suspend state request or signal, when required. 
         [0019]    Turning to  FIG. 2   a , a schematic diagram of apparatus for handling a charging state and/or a device suspend state in a mobile electronic device is shown. The apparatus may, for example, be implemented within the charger interface  14  of  FIG. 1 , and includes a battery charger enabling circuit  50 , a battery charger  52  and an inverting circuit  54 . In this example, the battery charger enabling circuit is a RS flip flop  50  and the inverting circuit is a field effect transistor (FET)  54 . The RS flip flop  50  includes an S port  56 , an R port  58 , a Vcc port  60 , a Q port  62  and a Q_bar port  64 . The battery charger  52  includes a CE_bar port  66  (connected to the Q_bar port  64 ), a Vcc port  68  and a BAT port  70 . Both the RS flip flop  50  and the battery charger  52  are connected to ground  72 . A USB VBUS input  74  is connected to the S port  56  via a delay  76  and the Vcc ports  60  and  68  of the RS flip flop  50  and the battery charger  52 , respectively. 
         [0020]    In the illustrated example, the delay  76  is implemented with a resistor-capacitor (RC) circuit, but may also be a voltage detector with a pre-set delay, or some other type of delay circuit. The delay  76  may, for example, be preset for 1 to 5 ms. 
         [0021]    The VBUS input  74  is also connected to the R port  58  of the RS flip flop  50  via a resistor  78  and to ground  72  via the resistor  78  and a capacitor  80 . The values of the resistor  78  and the capacitor  80  may be selected so that they form a 100 ms timer  82 , in accordance with the time allotted by the USB specifications for drawing power from a USB host without receiving an enumeration acknowledgement signal from the USB host. This timer represents the time period within which an acknowledgement of enumeration is expected from the USB host CPU  32  by the system  12 . 
         [0022]    The BAT port  70  of the battery charger  52  is connected to the CPU  12  and the rechargeable battery  16  to provide the necessary current/voltage from the VBUS input for both powering the mobile electronic device  10  and for recharging the battery  16 . In the case the battery is not present, there is only current/voltage transmitted to the CPU  12 . 
         [0023]    An output  84  from the CPU  12  is connected to the R port  58  of the RS flip flop  50  via the FET  54 . The output  84  is generally a signal which allows the system to enable or disable the battery charger  52  and to switch between the device charging state and the device suspend state. 
         [0024]      FIG. 2   b  is a block diagram of a second example apparatus for handling the charging state/device suspend state in a mobile electronic device. This example is similar to the example shown in  FIG. 2   a , except that the inverting circuit is an inverter logic gate  90 . 
         [0025]      FIG. 2   c  is a block diagram of a third example apparatus for handling the charging state and/or device suspend state in a mobile electronic device. This example is similar to the examples of  FIGS. 2   a  and  2   c , except that the inverting circuit is a bipolar transistor  92 . 
         [0026]    Turning to  FIG. 3 , a flow diagram showing an example method of handling a device charging state in a mobile electronic device is shown. In order to determine if the mobile electronic device has entered the device charging state, a check is performed to sense if inputs to the charger interface  14  are in a low state. When the inputs are in a low state, the indication is that there is no power being transferred to the CPU  12  indicating that the battery  16  is dead or not present. The output  84  from the CPU  12  is transmitted as a low state signal and there is no voltage at the input  74 . 
         [0027]    After sensing that the inputs to the charger interface  14  are at a low state, the rising edge of the VBUS input  74  (supplied by the power source  30  in the USB host  22 ) is sensed (step  100 ) by the Vcc port  60  of the RS flip flop  50 . This step is repeated until the rising edge of the VBUS input  74  is sensed (e.g., when the USB cable is connected between the mobile electronic device  10  and the USB host  22 .) 
         [0028]    Once the USB cable  24  is connected between the mobile electronic device  10  and the USB host  22 , power from the USB VBUS input  74 , in the form of a current/voltage, is transmitted from the power source  30  via the USB cable  24  to the mobile electronic device  10 . When the power is applied at the input  74 , the VBUS input  74  input may be seen as a high state signal. 
         [0029]    Once applied, the input  74  is sensed by the Vcc port  60  of the RS flip flop  50  which causes the RS flip flop  50  to be initially powered. The USB VBUS input  74  also transmits the high signal to the S port  56  of the RS flip flop  50  after passing through the delay  76 . The delay allows the RS flip flop  50  to be enabled by the input  74  without interruption by inputs at the S or R port  56  and  58 . The high state signal received by the port  56  causes the Q_bar port  64  to transmit a low state signal to the CE_bar port  66  enabling the battery charger  70  (step  102 ). The battery charger  70  then transmits power, in the form of a current, via the BAT port  70  to the system to power up the mobile electronic device  10  and to the battery  16  to recharge the battery. 
         [0030]    Once the CPU  12  receives this current, the CPU  12  responds to an enumeration request from the USB host CPU  32  via the data lines in the USB cable  24 . 
         [0031]    While the battery charger  52  is being enabled, the timer  82  is also enabled (step  104 ) by the VBUS input  74 . The timer  82  is set to a pre-determined time period (determined by the selection of the resistor and capacitor values), such as 100 ms. A check is then performed to verify that the timer  82  has not expired (step  106 ). 
         [0032]    When the VBUS input  74  is transmitted from the power source  30  to the mobile electronic device  10 , the capacitor  80  charges due to the capacitor being in the series with the resistor  78 . The value of the resistor  78  and the capacitor  80  in the timer  82  are selected so that the capacitor becomes charged (reaches a high state threshold) after the predetermined time period (e.g., 100 ms.) 
         [0033]    If the timer  82  has expired (i.e. has not been disabled before the period of 100 ms has elapsed), the high state threshold from the voltage on the capacitor causes the input at the R port  58  to be high which, in turn causes the Q_bar port  64  to transmit a high signal to the CE_bar port  66  to disable the battery charger  52  (step  108 ). This performs the function of a watchdog timer which verifies that enumeration between the system and the USB host has been acknowledged during the predetermined time period. The device then returns to the step of sensing the rising edge of the VBUS input (step  100 ). 
         [0034]    If the timer  82  has not expired, whereby the high state threshold on port R  58  has not been met, a check is performed to determine if enumeration between the system  12  and the USB host CPU  30  has been acknowledged (step  110 ). That is, a check is performed to verify whether or not the CPU  12  has received acknowledgement from the USB host to draw current from the power source  30 . If enumeration has not been acknowledged, verification that the timer has not elapsed is once again performed (step  106 ). 
         [0035]    If the enumeration request has been acknowledged, the system (e.g., CPU)  12  transmits a high state signal  84  to the inverting means, seen as the FET  54  in the preferred embodiment, which then sends a low state signal to the R port  58  of the RS flip flop  50  causing the battery charger  52  to remain enabled and the mobile electronic device  10  to enter the device charging state (step  112 ). This output  84  also overrides the charging of the capacitor  80  by short circuiting the capacitor so that the battery charger  52  is not erroneously disabled after the predetermined time period. 
         [0036]    When the system (e.g., CPU)  12  of the mobile electronic device receives a suspend state request from the CPU  32  in the USB host  22 , the output  84  from the system (e.g., CPU)  12  is driven to a low state signal which turns off FET  54  allowing resistor  78  to charge capacitor  80 , both inside timer circuit  82 . When capacitor  80  reaches the high state threshold of port R  58 , this causes the RS flip-flop to reset and transmit a high state signal from the Q_bar port  64  to the CE_bar port  66  disabling the battery charger  52 . Since the battery charger  52  is providing power to the system  12  when the battery  16  is dead or not present, the system (e.g., CPU)  12  is powered down and the VBUS current from the VBUS input drops below 500 μA as required by USB suspend state specifications. 
         [0037]    This written description uses examples to disclose the invention, including the best mode, and also to enable a person skilled in the art to make and use the invention. The patentable scope of the invention may include other examples that occur to those skilled in the art.