Abstract:
A method to detect the presence of battery protection circuits in any battery powered product. The major advantage of the method is to make the battery voltage very smooth during the charging process. The proposed circuit can give a good prediction of protection switching turn on time. This can provide the battery powered system work smoothly by avoiding any battery voltage discontinuity. The proposed invention addresses the issue of deep discharge and provides a solution through a discharge test procedure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is directed to detection of battery protection circuits in an electronic device. More specifically it is directed towards outputting a smooth battery voltage to a load during the process of charging an electronic device, including mobile devices. 
         [0003]    2. Related Art 
         [0004]    The current battery charging technology does not detect the level of charge already present in a battery, before the charging process begins. Thus, due to an unknown level difference between the actual battery voltage and the assumed battery voltage level which is initially supplied to the battery, there is often a high probability of the battery output voltage suffering a discontinuity. This can result in improper functioning of the load device. For example, in case of a cellular phone, such a voltage discontinuity at the output of a battery due to sudden surge in charge voltage can lead to dropped calls or a discontinuity in communication. 
         [0005]    The conventional battery charger circuits also do not provide a solution for what is known in the art as deep discharge of the battery. Thus, there is need for the battery charger to have an inbuilt test strategy to determine the level of battery charge. 
         [0006]    The battery chargers in the market cannot detect the protection circuits inside the battery very well. As a result, there is no decision possible with respect to whether a battery should be trickle charged or charged at full voltage. This may lead to overcharging or undercharging the battery. Both of these situations not only effect the battery life but may also be detrimental to the load life or the functions it performs. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The invention is directed towards a method and apparatus to detect the presence of battery protection circuits in a battery. The invention aims to substantially obviate one or more of the problems and disadvantages of the related art. 
         [0008]    In one embodiment, there is provided a protector Integrated Circuit (IC) inside the battery which controls the turning on and off of two transistors which control the current flow to the battery. In a realistic scenario, the battery can discharge to a level which is very low as compared to the under voltage ratio defined for the battery. This is known as the Deep Discharge Scenario. If the battery is in the deep discharge zone and a charger is then connected to it, it will start charging at a high voltage level. As soon as the battery level crosses the under voltage level, there is a sudden drop in the output of the charger. The charger now drops to the battery voltage level, which is now equal to the under voltage level. This sudden drop in the voltage level causes discontinuities in the output of the battery. 
         [0009]    To avoid discontinuity in the output of the battery, or to at least minimize it, the battery charger must determine the battery charge prior to the commencement of the charging process. To help the charger determine the correct battery voltage to be supplied, the invention tests when the battery protection circuit is enabled. In another embodiment, this test procedure is in-built in the Power Management Unit (PMU) of which the battery protection circuit may be a part of. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
         [0010]    The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements and in which: 
           [0011]      FIG. 1  illustrates a battery protector circuit. 
           [0012]      FIG. 2A  illustrates a charging mode of the battery protection circuit. 
           [0013]      FIG. 2B  illustrates a discharging mode of the Battery Protection Circuit. 
           [0014]      FIG. 3  illustrates the voltage drops with respect to time in a Deep Discharge Scenario. 
           [0015]      FIG. 4  illustrates a test flow chart to determine the charging technique to use. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  illustrates a battery protection circuit  100 , according to one embodiment of the invention. Battery protection circuit  100  shows a battery pack  102  with a peak voltage output V PP    110  and a low voltage output V PN    112 . The battery pack  102  includes, among other elements, a protector IC  104  connected to a charge current path CC  106  and a discharge current path DC  108 . The charge current path CC  106  is connected to the gate of a first transistor  114 . The discharge current path DC  108  is connected to the gate of a second transistor  116 . 
         [0017]    The drain of the first transistor  114  is connected to the peak voltage output V PP    110  and the source of the first transistor  114  is connected to the drain of the second transistor  116 . Between the drain and the source of the first transistor  114 , a first diode  122  is connected such that the cathode of the first diode  122  is connected to the drain of the first transistor  114  and the anode of the first diode  122  is connected to the source of the first transistor  114 . 
         [0018]    As follows from what is described immediately above, the drain of the second transistor  116  is connected to the source of the first transistor  114 . The source of the second transistor  116  is connected to the positive terminal of a battery  118  at node  126 . Between the collector and the source of the second transistor  116 , a second diode  120  is connected such that the cathode of the second diode  120  is connected to the source of the second transistor  116  and the anode of the second diode  120  is connected to the drain of the second transistor  116 . 
         [0019]    Negative terminal of the battery  118  is connected to the low voltage output V PN    112 . The Battery Protection Circuit  100  functions according to a voltage V MBAT    124  across the positive and the negative terminals of the battery  118 . The first transistor  114  and the second transistor  116  provide protection to the battery  118  from overcharging or going into a deep discharge mode, depending upon the voltage V MBAT    124  of the battery  118 . The protector IC  104  provides the logic to control the turn ON and turn OFF of the first transistor  114  and the second transistor  116 . 
         [0020]    The Battery Protection circuit  100  serves as a communication port between the battery  118  and a mobile device (not shown in any figure), of which the battery  118  and the Battery Protection Circuit  100  is a part and to which the battery  118  supplies power. 
         [0021]      FIG. 2A  illustrates a charging mode of Battery Protector Circuit  100  of  FIG. 1  (and thus how an overcharge mode is avoided). An overcharge mode is defined as the condition when the voltage V MBAT    124  across the terminals of the battery  118  is greater than an over-voltage threshold V OV . Overcharging should be avoided since it can produce hydrogen in the battery, which can be very dangerous. According to one embodiment, the over-voltage threshold V OV  is set equal to 4.242 Volts, but other voltages are contemplated. In such a condition if the peak value of the voltage V MBAT    124  is below V OV , the protector IC  104  (not shown in  FIG. 2A ) will turn ON the first transistor  114  by means of the charge current path CC  106 . As a result, a current i oC  will flow along the path  202 , as shown in  FIG. 2A , thus charging the battery. Since the protector IC  104  does not assert any signal on the discharge current path DC  108 , the second transistor  116  is turned OFF. The current i oC  flows through the second diode  120 , which is forward biased. When V MBAT    124  goes above V OV  the battery is at full capacity and first transistor  114  will be turned off to prevent further charging. 
         [0022]      FIG. 2B  shows illustrates a discharging mode of Battery Protector Circuit  100  of  FIG. 1  (and thus how a deep discharge mode is avoided). The protector IC  104  of  FIG. 1  will turn ON the second transistor  116  by means of the discharge current path  108 . As a result, a current i dis  will flow along the path  204 , as shown in  FIG. 2B . Since the protector IC does not assert any signal on the charge current path CC  106 , the first transistor  114  is turned OFF. The current i dis  flows through the first diode  122 , which is forward biased. Thus, the battery can discharge when the second transistor is ON. 
         [0023]    A deep discharge mode is defined as the condition when the voltage V MBAT    124  across the terminals of the battery  118  is less than an under-voltage threshold V UV . The value of the under-voltage threshold V UV  is usually set to a very low value. When the voltage V MBAT    124  falls below the under-voltage threshold V UV , the battery  118  is in a deep discharge zone. The battery must be recharged when the battery enters the deep discharge zone. In such a circumstance, second transistor  116  must be turned OFF to prevent further discharging. 
         [0024]      FIGS. 2A and 2B  illustrate the charging and discharging operations of the battery  118 . For example, if the protector IC  104  of  FIG. 1  detects that the voltage V MBAT    124  is too low, it disables the second transistor  116  thereby enabling the path  202  of the circuit, so that the battery  118  can charge. Similarly, if the protector IC  104  of  FIG. 1  detects that the voltage V MBAT    124  is too high, it disables the first transistor  114  thereby enabling the path  204  so that the battery  118  can discharge. 
         [0025]      FIG. 3  shows a voltage versus time plot  300  for the battery  118  of  FIG. 1 . The Voltage V  302  is shown to vary with respect to Time  304  in a manner shown by curve  326 , curve  324  and curve  322 . Before the battery  118  of  FIG. 1  is set to charging, the exact value of the voltage of the battery  118  is unknown. It could be anywhere from 0 volts to V UVHL    332 . The region of the voltage versus time plot  300  between the abscissa and the line  320  is known as the deep discharge zone. In the deep discharge zone, the transistor  116  of  FIG. 1  is OFF as shown by QD off  316 . In such a situation, the battery  118  will start charging to the peak voltage output V PP    110 . 
         [0026]    The value of the peak voltage output V PP    110  is higher than a trickle charge voltage threshold V TR    328  shown as a line  312  in the voltage versus time plot  300 . Between a voltage V UVLH    330  and the trickle charge voltage threshold V TR    328 , the battery  118  charges in a trickle charge TR mode  310 . As is known in the art, a trickle charge process usually occurs at a fraction of the total charge value of the battery  118 , to compensate for losses due to phenomena like self-discharge. 
         [0027]    As soon as the battery  118  attains a voltage corresponding to a charge value that is higher than the trickle charge voltage threshold V TR    328 , at a time t  306 , the second transistor  116  turns ON resulting in a sharp voltage drop shown by the curve  324 . The voltage drop shown by the curve  324  leads to disruptions in the output power of the device connected to the battery  118 . For example, due to the sudden turn ON of the second transistor  116 , in a cell phone device, there might be a sudden drop in the audio output from the cell phone speaker/ear-piece. After the voltage drop shown by the curve  324 , the battery  118  starts recharging back to a value higher than the trickle charge voltage threshold V TR    328  as shown by the curve  322 . Extending the curve  322  below the value V UVLH    330  shown by line  314  in the voltage versus time plot  300  shows that curve  322  originates from a value of the voltage V MBAT    124  corresponding to the actual voltage value the battery  118  was at before the charging process was initiated. 
         [0028]    To avoid the above mentioned discontinuity in the output power of the device due to a sudden change in the battery voltage level, a discharge test is performed. This test procedure is built in a power management unit, external to the Battery Protection Circuit  100 , that is a part of the mobile device to which the battery  118  of  FIG. 1  is supplying power to. There is provided a provision for communication between the external power management unit and the Battery Protection Circuit  100  of  FIG. 1 . 
         [0029]      FIG. 4  shows a flowchart  400  that performs a discharge test. In step  402  a trickle charge timer T TR  is set to an expire time, usually 1 hour (but other expiration times are contemplated). As a preliminary step, the external power management unit checks if a battery  118  is present or not, in the first place, by detecting a thermal resistance. If a battery  118  is detected, the external power management unit checks for the value of the peak voltage output V PP    110 . Only if the value of the peak voltage output V PP    110  is less than a discharge test threshold voltage V DTTH , does a charge controller perform a discharge test, as shown in step  404 . According to one embodiment of the present invention, the value of the discharge test threshold voltage V DTTH  is set in the range of 2.0 volts to 2.5 volts. It is to be noted that depending upon the type of application and the type of the battery  118  of  FIG. 1 , other values of the discharge test threshold voltage V DTTH  can also be selected. 
         [0030]    In step  404 , a discharge step is performed by the external power management unit. It involves the following steps: 
         [0031]    (a) turning off the Battery Pack  102  and then discharging the battery  118  of  FIG. 1 . 
         [0032]    (b) if the second transistor  116  is OFF, the peak voltage output V PP    110  will be 0 volts when the battery  118  is being discharged. 
         [0033]    (c) if the second transistor  116  is ON, the peak voltage output V PP    110  will be the real battery voltage equal to V MBAT    124  of  FIG. 1 . In this case a discharge path is closed, as can also be seen from  FIG. 2A . 
         [0034]    In step  406 , if the discharge path is closed, a normal charging procedure is followed according to step  408 . If the discharge path is not closed, a discharge test period T P(DISCH)  is set equal to 5 minutes and the battery  118  is trickle charged for that duration of time, according to step  410  of the flowchart  400 . After the T P(DISCH)  time period expires, control moves back to step  404  where the conditions set forth in the steps  404  and  406  are repeated till the discharge path, as mentioned in step (c) of step  404 , is closed, such that control passes to step  408 . 
         [0035]    By means of the test procedure described in flowchart  400 , the discontinuities in the output of the mobile device due to charging of the battery  118  are avoided. 
         [0036]    It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.