Abstract:
Disclosed is a mobile device comprising a voltage supervisor and reset (VSAR) module configured to detect an input voltage, start a timer set to a predetermined time period responsive to detecting the input voltage, and output a low signal responsive to detecting the input voltage. The mobile device also comprises a battery charger module configured to receive the input voltage, receive the low signal, output a power signal, and charge a battery. The mobile device also comprises a processing module configured to receive the power signal, and attempt enumeration responsive to receiving the power signal, wherein the VSAR module is further configured to output a high signal to the battery charger module when the timer expires and enumeration has not been completed.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to mobile electronic devices and more specifically to a method and apparatus for setting of a charging state in a mobile electronic device. 
     BACKGROUND OF THE INVENTION 
     Portable systems, such as mobile electronic devices, which are powered by rechargeable batteries have a problem supporting both USB (Universal Serial Bus) charging and suspend functions. 
     In operation, USB specifications require that any devices which are connected to a USB host initiate enumeration within ˜150 msec of a USB cable being attached, hereon referred to as “VBUS detection”. Enumeration is the process whereby devices attached to the USB host request permission to access the host. In the present invention, the enumeration request is directed to a request to draw power from the USB host in order to power up the mobile electronic device which has a dead or non-present battery. 
     When the rechargeable battery is dead or not present, the mobile electronic device can not operate since it does not have any power. In most cases, it is desired that a battery charger within the mobile electronic device turn on once it receives power from the USB VBUS power line upon VBUS detection. This causes the charger to be enabled so that power is supplied from the USB host 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 charger turns on and acts as the battery to power the CPU along with charging the battery. In this case, all the signals to the battery charger are in a low state. 
     Another common state for the mobile electronic device is a device suspend state. USB specifications require that a total USB supply current to the mobile electronic device not exceed 500 μA in the device suspend state. With many mobile electronic devices, 500 μA is not enough current for the CPU of the mobile electronic device to operate and therefore the device should be powered down. Powering down of the CPU causes all the control signals to default to a low logic level state, which would then keep the charger on. This state of the charger is not desirable for the system, during a device suspend state. In some prior art devices, two separate signals to control the device charging state and the device suspend state are used. 
     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 by the mobile electronic device even though it is required under the USB specifications. 
     Therefore, there is provided a method and apparatus for handling a charging state in a mobile electronic device. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides a method of handling a device charging state for a Universal Serial Bus (USB) connected mobile electronic device comprising the steps of sensing presence of a bus voltage, sensing an enumeration acknowledgement signal between said device and a USB host, and transmitting a signal to instruct said device to enter said device charging state. 
     In another aspect of the invention, there is provided a method of entering a device charging state for a mobile electronic device connected to a USB host, comprising the steps of sensing an input voltage from said USB host, transmitting a time dependent enable signal to a battery charger, requesting enumeration from said USB host, receiving enumeration acknowledgement from said USB host, verifying that said time dependent enable signal has not elapsed, and transmitting an enumeration acknowledged enable signal to said battery charger overriding said time-dependent enable signal if said time dependent enable signal has not elapsed. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1  is a block diagram of a mobile electronic device connected to a Universal Serial Bus (USB) host. 
         FIG. 2  is a flow diagram outlining a method of handling a device charging state for a mobile electronic device. 
         FIG. 3  is a block diagram of prior art apparatus for handling a charging state in a mobile electronic device. 
         FIG. 4  is a block diagram of apparatus for handling a device charging state for a mobile electronic device. 
     
    
    
     DETAILED DESCRIPTION 
     Turning to  FIG. 1 , a block diagram of a mobile electronic device connected to a Universal Serial Bus (USB) host is shown. The mobile electronic device  10  comprises a central processing unit (CPU)  12  connected to a charger interface  14  which, in turn, is connected 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 . 
     During operation of the mobile electronic device  10 , when a user determines that the rechargeable battery  16  is dead or not present, the user connect the mobile electronic device  10  to the USB host  22  via a USB cable  24 . Within the USB cable  24  are four separate cables: 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 , preferably a mobile electronic device interface, is connected to the USB host port  26  for transmitting data and current to and receiving data from the mobile electronic device  10 . The USB host  22  further comprises a power source  30  and a CPU  32  which are both connected to the device interface  28 . 
     Turning to  FIG. 2 , a method of switching between a device suspend state and a device charging state for the Universal Serial Bus (USB) connected 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  and therefore no power for operating the device  10 . As will be understood, the device may be turned off, the rechargeable battery  16  is dead or not present or the user may have placed the device in the device suspend mode. Therefore, after sensing that the inputs to the charger interface have been set at a low state, the status and level of a bus voltage (supplied by the power source  30  in the USB host) is sensed (step  34 ). The bus voltage is provided when the USB cable is connected between the USB host and the mobile electronic device. If the bus voltage is not sensed, a voltage supervisor continues to monitor for the presence of the bus voltage. 
     If the bus voltage is sensed, the battery charger is then enabled (step  36 ). After enabling the battery charger, a timer is then enabled (step  38 ), and set to a pre-determined time period, preferably at least 100 msec. Once the timer is set, it begins to count down. A check is then performed to verify that the timer has not expired (step  40 ), i.e., that the predetermined time period has not elapsed. If the timer has expired, the battery charger is then disabled (step  42 ) and the device returns to the step of sensing the bus voltage (step  34 ). If the timer has not expired, a check is performed to determine if enumeration between the CPU and the USB host has been acknowledged (step  44 ). In other words, a check is performed to verify whether or not the CPU has transmitted a signal requesting the battery charger to remain enabled. If enumeration has not been acknowledged, verification that the timer has not elapsed is once again performed (step  40 ), and the battery is disabled (step  42 ) where the timer has elapsed. 
     However, if enumeration has been acknowledged within the predetermined time period from the sending of the status and level of the bus voltage, the CPU sets the device into the device charging state (step  46 ) and both powers the CPU and charges the battery using the bus voltage provided by the power source. 
     Turning to  FIG. 3 , prior art apparatus for handling a device charging or device suspend state is shown. The apparatus  50  comprises a battery charger  52  connected via its Vcc gate  54  to the VBUS power line from the USB host  22 . A BAT gate  56  is connected to the CPU  12  along with the rechargeable battery  16 . The CPU  12  is also connected to a CE_bar gate  58  of the battery charger  52 . 
     When the battery is dead or not present, the mobile electronic device  10  is connected to the USB host  22  ( FIG. 1 ), via the USB cable, to supply the VBUS voltage via the power line. It will be understood that the rechargeable battery is preferably decoupled from the mobile electronic device  10  in order to start the CPU  12  and that recoupling may occur at any time without affecting the operation of the device as long as power is provided by the VBUS power line. 
     A system control signal  60  (seen as CHRG_EN_bar) from the CPU  12  is transmitted to the battery charger  52  to enable the charger when the VBUS is applied. This signal is typically a low state signal. The prior art apparatus does not wait for an enumeration acknowledgement and automatically enters the device charging state. In general, this goes against USB specifications. Therefore, when the rechargeable battery  16  is dead or not present and the CPU  12  has no power, the CHRG_EN_bar signal  60  is low and since the charger requires an active low state signal to enable the charging function, the battery charger  52  enables and provides power (in the form of current received from the VBUS power line) to the CPU  12 . When the USB host transmits a device suspend state request, the prior art circuit is unable to handle this request is the battery is dead or not present. 
     Turning to  FIG. 4 , a block diagram of an embodiment of the charger interface in  FIG. 1  is shown. The charger interface  14  comprises an input  100  from the VBUS power line which is connected to a Vcc gate  102  of a Voltage Supervisor and Reset module  104 . In the preferred embodiment, the voltage supervisor and reset module  104  is a TPS3103 chip manufactured by Texas Instruments. The voltage supervisor and reset module  104  also comprises a MR_bar gate  106  and a RST_bar gate  108 . The VBUS input  100  is also connected to a Vcc gate  110  of a battery charger  112 . The RST_bar gate  108  is connected to a CE_bar gate  114  of the battery charger  112  while a BAT gate  116  of the battery charger  112  is connected to the rechargeable battery  16  via the CPU  12 . The CPU  12  is also connected to the MR_bar gate  106  of the voltage supervisor and reset module  104  via a NOT gate (or inverter)  118 . It will be understood that the signals being received at the MR_bar gate  106 , the RST_bar gate  108 , the CE_bar gate  114  and the NOT gate  118  are binary inputs so that the signal is either a low state (0) or a high state (1) signal. 
     In operation, when the rechargeable battery is dead or not present, in order to provide power for operation of the mobile electronic device  10  ( FIG. 1 ), the USB cable  24  is connected to the USB port  20  of the mobile electronic device  10 . Once connected, the voltage supervisor and reset module  104  checks the status and level of the input  100  from the VBUS power line. The check is performed by the Vcc gate  102  of the voltage supervisor and reset module  104 . After sensing the presence of the input  100 , a timer  103  within the voltage supervisor and reset module  104  is started to determine when a predetermined time period, as described above, has elapsed. The timer  103  may be implemented in a number of ways, digitally or by analog means (with an RC circuit, for example). This predetermined time period is used to determine whether the mobile electronic device  10  has received an enumeration acknowledgement from the USB host  22  to draw power from the USB host via the VBUS input power line. A continuous check is performed by the voltage supervisor and reset module  104  to determine if the timer has expired. 
     During this predetermined time period, the CPU  12  is powered from the power source  30  in the USB host  22 . This allows the charging process to begin before the enumeration is completed. Within the predetermined time period, the CPU  12  is required to enumerate with the USB host  22  to continue drawing current to power the device  10  and charge the battery. 
     After sensing the presence of the input  100 , the voltage supervisor and reset module  104  transmits a low state (0) signal from its RST_bar gate  108  to the CE_bar gate  114  of the battery charger  112  to enable the battery charger  112 . The battery charger  112  then transmits a voltage (current) to the CPU  12  and the rechargeable battery  16  using the current received in its Vcc gate  110  from the input  100 . Once the CPU  12  receives the current, the CPU  12  requests enumeration from the USB CPU  32  in the USB host  22 . Once it receives an enumeration acknowledgement, the CPU  12  transmits a high state CHRG_EN signal to the inverter  118  which inverts the signal to a low state signal before transmitting it to the MR_bar gate  106 . If the low state signal is not received by the MR_bar gate  106  prior to the end of the predetermined time period, the voltage supervisor and reset module  104  transmits a high signal from its RST_bar gate  108  to the CE_bar gate  114  to disable the battery charger  112 . In order to verify whether the timer is expired, resulting in the disabling of the battery charger, the initial low state signal transmitted from the voltage supervisor and reset module  104  to the battery charger, is set for the predetermined time period and once the time period expires, the low state signal is switched to a high state signal which disables the battery charger. 
     However, if the enumeration is acknowledged before the expiration of the timer, the voltage supervisor and reset module  104  transmits a low state signal to the CE_bar gate  114  and the battery charger  112  remains enabled so as to receive the input  100  and supply the necessary current for powering the mobile electronic device  10  and for charging the battery  16 . 
     The enablement of the battery charger  112  continues until the USB cable is disconnected from the USB port  20  or if a device suspend signal is transmitted along the data lines of the USB cable  24  from the USB CPU  32  to the CPU  12  of the mobile electronic device  10 , indicating that the USB host  22  requests that the mobile electronic device  10  enter the device suspend state. After receiving the request, in order to comply with USB specifications, the CPU  12  transmits a low state CHRG_EN signal to the inverter  118  which inverts the low state signal to a high state signal. The high state signal is then transmitted to the MR_bar gate  106  which causes the RST_bar gate  108  to transmit a high signal to the CE_bar gate  114  of the battery charger thus disabling the battery charger as requested by the USB host  22 . 
     When the high state signal is received by the MR_bar gate  106 , the signal is not immediately propagated. The timer  103  counts down for a second predetermined time period, such as 150 msec, so that if a subsequent low state signal is received by the MR_bar gate within the second time period, the high state signal is ignored. This allows the CPU  12  to reset without losing power to the battery charger  112 . In general, when the CPU resets, all signals go to a low state. In this manner, a reset event does not cause the charger to be disabled since a reset event is not a device suspend state event. 
     An advantage of the present invention is that if the CPU  12  fails to receive enumeration acknowledgement to enable the battery charger  112  prior to the predetermined time period timer elapsing, the battery charger is automatically disabled. Therefore, the mobile electronic device  10  does not continue to draw power from the power source  30  in the USB host  22 . This provides an added function so that the CPU  12  of the mobile electronic device does not inadvertently draw current without proper enumeration. 
     Another advantage of the present invention is that when the CPU  12  in the mobile electronic device  10  is instructed by the CPU  32  in the USB host  22  to enter the device suspend state, the CPU  12  disables the battery charger  112  by transmitting the low state signal to the inverter  118  and which is subsequently transmitted as a high state signal to the MR_bar gate of the voltage supervisor and reset. If the timer  103  has expired, and there is no change of the input from the VBUS power line, the battery charger is disabled even though VBUS is still present as required by USB specifications. When the battery charger is disabled, and the rechargeable battery  16  is not fully recharged, there is no power transmitted to the CPU  12  and although all of the state signals are active in the low state, the signals do not cause the battery charger to become enabled as was the situation with the initial USB cable connection. 
     Furthermore, another advantage of the present invention is that only one signal is required to switch the mobile electronic device from the device charging state to the device suspend state. 
     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.