Abstract:
A system and method for using a universal serial bus (USB) interface in a mobile device is provided that includes providing a battery charger operable to receive a voltage provided at the USB interface, the battery charger operable for charging a battery in the mobile device, and, a voltage regulator operable to receive a voltage provided at the USB interface, the voltage regulator used in powering the mobile device. The method also includes, detecting a USB bus voltage at the USB interface, measuring passage of a predetermined amount of time upon detecting the USB bus voltage, and disabling at least one of the voltage regulator and the battery charger if the predetermined amount of time expires before an enumeration acknowledgement signal is received at the USB interface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This continuation application claims priority from U.S. patent application Ser. No. 11/026,590, 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-PAT-4214-00702) and U.S. Provisional Application No. 60/545,433, 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 technology described in this patent document relates generally to mobile electronic devices. More particularly, the patent document 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, USB specifications require that the device initiate enumeration within 100 msec, hereon referred to as “VBUS detection”. 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 further operable to receive an enumeration acknowledgement signal from the USB host via the USB interface. A rechargeable battery may be used for powering the processing device. A voltage regulator may be coupled to the USB interface and operable to receive a USB bus voltage from the USB interface and use the USB bus voltage to power the processing device. A timing circuitry may be used to disable the voltage regulator from powering the processing device after a pre-determined amount of time has expired, the timing circuitry being operable to measure the passage of the pre-determined amount of time upon detecting the USB bus voltage. A battery charger may be used to receive the 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 processing device may enable the battery charger to power the processing device and to charge the rechargeable battery when the enumeration acknowledgement signal is received from the USB host. 
     
    
     
       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  is a schematic diagram of an example apparatus for handling a charging state in a mobile electronic device; 
           [0013]      FIG. 3  is a flow diagram of an example method of handling a charging state in a mobile electronic device; and 
           [0014]      FIG. 4  is a flow diagram of another example method of handling a charging state in a mobile device. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      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 . 
         [0016]    The USB interface  18  interacts with the USB port  20  to receive data and power from and transmit data to the USB host  22 . 
         [0017]    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. 
         [0018]    Turning to  FIG. 2 , a schematic diagram of an example apparatus for handling a device charging state, in the form of the charger interface, is shown. The charger interface  14 , which receives a USB VBUS input  48 , includes a low dropout (LDO) regulator  50 , a battery charger  52  and a DIODE OR  54 . The LDO regulator  50  is connected to the DIODE OR  54  via a P field effect transistor (PFET)  56  with a corresponding pull-up resistor  57 . The interface  14  further includes a capacitor  58  which is connected to ground  60  via two separate paths. One path to ground is via an N field effect transistor (FET)  62  and a second path to ground is via a resistor  64 . The PFET  56  is also connected to ground  60  via the NFET  62 . The battery charger  52 , including a Vcc port  66 , a charger enable (CE) port  68  and a battery (BAT) port  70  connected to the rechargeable battery  16  and the DIODE OR  54 . An output  72  of the DIODE OR  54  is connected to the system (e.g. the CPU)  12 . A first output  74  from the CPU  12  is connected to the CE port  68  of the battery charger  52  for enabling and disabling the charger  52  while a second output  76  from the CPU  12  is connected to ground  60  via the resistor  64  along with the LDO regulator  50  via the capacitor  58 . It should be understood that although the ports of the battery charger have been given specific labels, these labels are not meant to narrow the scope of the invention but to provide description as to the function of each port. 
         [0019]    In operation, when the USB cable  24  is connected between the USB port  20  of the mobile electronic device  10  and the USB host port  26  of the USB host  22 , the power source  30  transmits a current via the power line of the USB cable  24  to the charger interface  14  which is seen in  FIG. 2  as the USB VBUS input  48 . A continuous check is performed by the mobile electronic device until the rising edge of the input  48  is sensed. 
         [0020]    After the rising edge of the input  48  has been sensed, the input  48  is transmitted to the Vcc port  66  of the battery charger  52 , to the NFET  62  via the capacitor  58 , and to the LDO regulator  50  in order to enable a battery charger power path and a LDO regulator power path (step  102 ). The capacitor  58  passes the rising edge of the VBUS input  48  to the gate of the NFET  62 , which drives the NFET  62  to close the PFET  56  allowing the VBUS input  48  to through the LDO regulator  50  and the PFET  56  to the DIODE OR  54 . 
         [0021]    After receiving the VBUS input  48  at its Vcc port  66 , the battery charger  52  may remain disabled until it receives instructions from the CPU  12  to enable. Transmission of the input  48  to ground  60  via the capacitor  58  and the resistor  64  enables a timer. The values of the capacitor  58  and the resistor  64  are selected so that they form a 100 msec timer as required by USB specifications. 
         [0022]    A check is then performed to verify whether or not the timer has expired. If the timer has expired, the battery charger and LDO regulator power paths are disabled. Therefore, if the second output  76 , seen as a high state signal, is not transmitted from the system  12  to the NFET  62  before the expiry of the 100 ms timer, the resister  60  drains the gate of the NFET  62  which causes the PFET  56  to close which, in turn, disables the power path provided by the LDO regulator  50  since the current from the PDO regulator flows through the pull-up resistor  57  to ground  60  instead of the PFET  56 . 
         [0023]    While the resistor  64  drains the port of the NFET  62 , the CPU  12  transmits the first output  74 , in the form of a low state signal, to the CE port  68  of the battery charger  52  to disable the power path provided by the battery charger  52 . 
         [0024]    However, if the timer has not expired (there is still current for the system of the mobile electronic device to operate), the DIODE OR  54  selects a power path and transmits the power supplied by this path to continually power the system  12 . 
         [0025]    The DIODE OR  54  acts as a switch to select whether the system  12  receives its power from the LDO regulator  50  power path or the battery charger  52  power path. The DIODE OR  54  simply selects the higher of the two inputs as the power path. In one example, the LDO regulator is a 3.3V LDO regulator  50  so the DIODE OR  54  selects power from the LDO regulator  50  until the output voltage from the BAT port  70  reaches a level of 3.3 V. The output voltage from the BAT port  70  may be boosted by a voltage booster to increase the output of the BAT port  70  in order for the battery charger power path to be selected as the power path in a faster time period. The voltage from the battery charger  52  may be selected as the power path for the system  12 , however, until the output voltage from the BAT port  70  of the battery charger  52  reaches a pre-determined level, the power path provided by the LDO regulator  50  allows the system to power up with little or no delay after USB cable  24  is connected between the USB host  22  and the mobile electronic device  10 . 
         [0026]    Upon receipt of power from the DIODE OR  54 , the system  12  powers up and responds to an enumeration request from the USB host CPU  32  within the USB host  22  via the data lines in the USB cable. 
         [0027]    After responding to the enumeration request and sending a reply, a check is preformed to see if enumeration has been acknowledged by the USB host CPU  32 . 
         [0028]    If enumeration has not been acknowledged, a check is then performed to see if the timer has expired and the step of selecting the power path by the DIODE OR is repeated. If enumeration is acknowledged, the mobile electronic device  10  enters the device charging state. Once the enumeration acknowledgement is received by the system  12 , the system transmits the first output  74 , in the form of a high state signal, to the CE port  68  instructing the battery charger  52  to remain enabled. The second output  76  is also set to a level high after enumeration. 
         [0029]    When a device suspend state request is received by the system  12 , the first output  74  is transmitted, in the form of a low state signal, from the system  12  to the CE port  68  of the battery charger  52  to disable the battery charger which, in turn, stops the BAT port  70  from both recharging the battery  16  and providing a power path for the system  12 . The system  12  also transmits the second output  76 , in the form of a low state signal, to the resistor  64  and the NFET  62  causing the NFET to drain, closing the PFET  56  and disabling the power path between the LDO regulator  50  and the DIODE OR  54 . In this manner, there are no power paths entering the DIODE OR  54  and thus, no power provided to either recharge the battery or power up the device allowing the device to enter the device suspend state. 
         [0030]    It should be understood that although an LDO regulator has been used as one of the paths for providing power, a switched mode power supply (SMPS) could also be used. Furthermore, this path may also include other current limiting features. 
         [0031]    Also, although a DIODE OR has been shown as the switching mechanism, other types of switches could also be used; for example circuits based on FETS or other transistors. 
         [0032]    It should be understood that the NFET  62  and the PFET  56  are only one example for implementing a voltage controlled switch and other implementations are contemplated and possible. 
         [0033]    Furthermore, the capacitor and the NFET may be replaced by a voltage detector integrated circuit so that the alternate power path is enabled on the rising edge of the VBUS input for a time period of approximately 100 msec and so that the system can receive enumeration acknowledgement from the CPU  32  in the USB host  22  to complete the enumeration process. 
         [0034]      FIG. 3  is a flow diagram of an example method of handling a charging state in a mobile electronic device. At step  100  the mobile device monitors the USB VBUS input for a rising edge. When a rising edge is detected, the method proceeds to step  102  to enable the battery charger path and LDO regulator path. The timer is then enabled at step  104 . 
         [0035]    The method determines if the timer has expired at step  106 . If the timer has expired, then the battery charger and the LDO regulator paths are disabled at step  108 , and the method returns to step  100 . Else, if the timer has not expired, then the method proceeds to step  110  to select either the LDO or the battery charger as the power path for the mobile device. For example, the DIODE OR  54 , described above with reference to  FIG. 2 , may be used to select the power path with the highest voltage level. 
         [0036]    At step  112 , the method determines if a USB enumeration has been acknowledged. If not, then the method returns to step  106 . Else, if a USB enumeration has been acknowledged, then the device may enter a charging state. For example, with reference to  FIG. 2 , the BAT output of the battery charger  52  may be enabled causing the DIODE OR  54  to select the BAT output as the power path for the mobile device. 
         [0037]      FIG. 4  is a flow diagram of another example method of handling a charging state in a mobile electronic device. At step  200  the mobile device monitors the USB VBUS input for a rising edge. When a rising edge is detected, the method proceeds to step  202  to enable the LDO regulator. While enabled, the LDO regulator may be used to power the mobile device. A timer is then enabled at step  204 . 
         [0038]    At step  212 , the mobile device monitors the USB host for an enumeration acknowledgement. If the timer expires (step  206 ) before an enumeration acknowledgement has been received form the USB host, then the LDO regulator is disabled at step  208  causing the mobile device to stop drawing power from the USB VBUS, and the method returns to step  200 . If enumeration is acknowledged before the timer expires, however, then the method proceeds to step  214  to enable the battery charger, disable the LDO regulator and enter a device charging state. 
         [0039]    At step  216 , the mobile device monitors the USB host for a device suspend request. If a device suspend request is received, then the charger is disabled at step  218  and the method returns to step  200 . 
         [0040]    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.