Patent Publication Number: US-7592778-B2

Title: Battery protection IC chip

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery protection IC chip, and particularly relates to a battery protection IC chip that constitutes a battery pack protection circuit capable of preventing a lithium-ion battery used as a power source for a mobile device from overcharge, overdischarge, and overcurrent. 
     2. Description of the Related Art 
     Many mobile devices employ lithium-ion batteries in their battery packs. Lithium-ion batteries are likely to have troubles in the event of overcharge, overdischarge, and overcurrent. Therefore, battery packs for lithium-ion batteries are provided with battery protection modules including battery protection circuits that prevent lithium-ion batteries from overcharge, overdischarge, and overcurrent. Such a battery protection circuit has a FET chip serving as an electronic switch that opens in response to overcharge, overdischarge, and overcurrent. The battery protection module includes a COB (Chip On Board) structure in which chips and wires are encapsulated by a synthetic resin part, and a discrete module structure in which a packaged element is installed. The battery packs are repeatedly rechargeable by an associated recharger. 
     [Patent Document 1] Japanese Patent Laid-Open Publication No. 2004-6524 
     There is a high risk of trouble if an overcurrent is applied to a lithium-ion battery from a recharger during charging, or if an overcurrent is applied to a mobile device from a lithium-ion battery during use of the mobile device. It is therefore preferable from a safety standpoint to take some measures against these events. For example, because a FET chip generates heat in the case of overcurrent, detecting the temperature of the FET chip and turning off the FET chip when the temperature of the FET chip rises to a predetermined temperature may be one of the measures. It is desirable to provide such a measure with no increase in production costs of battery protection modules, no additional parts, and a high detection accuracy. 
     SUMMARY OF THE INVENTION 
     In view of the forgoing, it is an object of the present invention to provide a battery IC chip. 
     The present invention provides a battery protection IC chip that comprises a protection section for protecting a battery during charging and discharging, and a temperature detector for detecting an ambient temperature, wherein the protection section is configured to turn off a charge control FET chip and a discharge control FET chip in response to a detection by the temperature detector of the ambient temperature reaching a predetermined temperature. 
     According to the present invention, the battery protection IC chip is mounted on the charge control FET chip and the discharge control FET chip. As the battery protection IC chip is adjacent to the charge control FET chip and the discharge control FET chip, the temperature detector can accurately detect the temperature of the charge control FET chip and the discharge control FET chip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a battery protection device comprising a battery protection module according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view illustrating the battery protection device of  FIG. 1 ; 
         FIG. 3  is a front cross-sectional view illustrating the battery protection module according to the first embodiment of the present invention; 
         FIGS. 4A and 4B  are enlarged views each illustrating a control IC chip mounted on first and second FET-SW chips; 
         FIG. 5  is a block circuit diagram of a control IC chip; 
         FIG. 6  is a circuit diagram of a temperature detector of  FIG. 5 ; 
         FIGS. 7A-7C  are graphs for illustrating operations of the temperature detector of  FIG. 6 ; 
         FIG. 8  is a perspective view illustrating a battery pack including the battery protection device of  FIG. 1 ; 
         FIG. 9  is an enlarged view illustrating the battery protection device of the battery pack of  FIG. 8 ; 
         FIG. 10  is a circuit diagram of the battery protection device of  FIG. 1 ; 
         FIG. 11  is an enlarged perspective view illustrating a control IC chip module according to a second embodiment of the present invention; 
         FIG. 12  is a perspective view illustrating the control IC chip module of  FIG. 11 ; and 
         FIG. 13  is a cross-sectional view illustrating the battery protection module of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description provides exemplary embodiments of the present invention with reference to the accompanying drawings. 
     First Embodiment 
       FIGS. 1 and 2  illustrate a battery protection device  100  according to a first embodiment of the present invention.  FIG. 3  illustrates a COB type battery protection module  110 .  FIG. 8  and  FIG. 9  illustrate a battery pack  200  in which the battery protection device  100  connected to a lithium-ion battery  201  is installed. In  FIGS. 8 and 9 , Z 1  indicates an inner side of the battery pack  200 , and Z 2  indicates a front side of the battery pack  200 . X 1 -X 2  indicates a length direction of the battery protection device  100 ; Y 1 -Y 2  indicates a width direction thereof; and Z 1 -Z 2  indicates a thickness direction thereof. The Z 1  side of the battery protection device  100  is the upper side, and the Z 2  side thereof is the lower side.  FIG. 10  is a circuit diagram of the battery protection device  100 . 
     Referring to  FIGS. 1 and 2 , the battery protection device  100  comprises a battery protection module  110 , a base printed board  150 , and a connector member  160 . The battery protection module  110  and the connector member  160  are mounted on the base printed board  150 . The circuit diagram of the battery protection device  100  illustrated in  FIG. 10  shows a circuit section of the battery protection module  110  and a circuit section of the base printed board  150  in separate dashed-line boxes. 
     Taking a look at terminals, the battery protection device  100  includes a battery negative terminal  101  connected to the lithium-ion battery  201 , a battery positive terminal  102  also connected to the lithium-ion battery  201 , a battery pack negative output terminal  103 , and a battery pack positive output terminal  104 . The terminals  101  through  104  are connected to terminals of the battery protection module  110  via wiring and terminals, which are described in greater detail below. 
     [Battery Protection Module  110 ] 
     Referring to  FIGS. 2 and 3 , in the battery protection module  110 , a control IC chip  120  serving as a battery protection IC chip, a first FET-SW chip  121 , a second FET-SW chip  122 , a resistance chip  123 , and capacitor chip  124  are disposed on a Z 1 -side face of a COB-compatible printed board  111  having a double-sided structure. 
     Referring to  FIGS. 4A and 4B , the first and second FET-SW chips  121  and  122  have gate terminals  121 G and  122 G and source terminals  121 S and  122 S disposed on upper faces, and have drain terminals (not shown) disposed on the entire surfaces of lower faces, respectively. The first and second FET-SW chips  121  and  122  are mounted side-by-side on a die pad  112 . The drain terminals are silver-pasted onto the die pad  112  formed on the printed board  111 . The control IC chip  120  is secured onto the adjacent first and second FET-SW chips  121  and  122  with a double-sided adhesive tape  128  so as to extend across the first and second FET-SW chips  121  and  122 . Because the area of the control IC chip  120  is smaller than the total area of the adjacent first and second FET-SW chips  121  and  122 , the gate terminals  121 G and  122 G and the source terminals  121 S and  122 S are exposed outside the control IC chip  120 . An Au wire  126 - 1  extends between the control IC chip  120  and the first FET-SW chip  121 . An end of the Au wire  126 - 1  is bonded to a terminal disposed on an upper face of the control IC chip  120 , while the other end is bonded to the gate terminal  121 G of the first FET-SW chip  121 . Likewise, an Au wire  126 - 2  extends between the control IC chip  120  and the second FET-SW chip  122 . An end of the Au wire  126 - 2  is bonded to a terminal disposed on the upper face of the control IC chip  120 , while the other end is bonded to the gate terminal  122 G of the second FET-SW chip  122 . Plural Au wires  126 - 3  are bonded at one end to the source terminal  121 S of the first FET-SW chip  121  and at the other end to a pad  113  on the printed board  111 . Likewise, plural Au wires  126 - 4  are bonded at one end to the source terminal  122 S of the second FET-SW chip  122  and at the other end to a pad  114  on the printed board  111 . An Au wire  126 - 5  is bonded at one end to another terminal disposed on the upper face of the control IC chip  120  and at the other end to a pad on the printed board  111 . 
     Referring to  FIG. 3 , the control IC chip  120 , the first and second FET-SW chips  121  and  122 , the resistance chip  123  (hidden from view in  FIG. 3 ), and the capacitor chip  124  disposed on the Z 1 -side face of the printed board  111  are encapsulated by a synthetic resin part  127 . Together with the control IC chip  120  arranged on the first and second FET-SW chips  121  and  122 , the Au wires  126 - 1  through  126 - 5  are encapsulated by the synthetic resin part  127 . 
     The control IC chip  120 , the first and second FET-SW chips  121  and  122 , the resistance chip  123 , and the capacitor chip  124  are connected to form a lithium-ion protection circuit shown in  FIG. 10 . 
     [Control IC Chip  120 ] 
     Referring to  FIG. 10 , the control IC chip  120  provides an overcharge detection function to turn off the first FET-SW chip  121  when an overvoltage is applied to the lithium-ion battery  201  due to some failure during charging, an overdischarge detection function to turn off the second FET-SW chip  122  when the voltage of the lithium-ion battery  201  drops to or below a predetermined voltage, an overcurrent detection function to turn off the first FET-SW chip  121  when a large current is applied due to a short circuit, and a temperature detection function to detect whether a temperature, such as ambient temperature or the temperature of one or more of the first and second FET-SW chips  121  and  122 , rises to a predetermined temperature. 
     For providing these functions, as shown in  FIG. 5 , the control IC chip  120  includes a first logic circuit  141 , a second logic circuit  142 , an overcharge detector VD 1 , an overdischarge detector VD 2 , a discharge overcurrent detector VD 3 , charge overcurrent detector VD 4 , a level shift circuit  143 , a delay circuit  144 , a short circuit detector  145 , an oscillator  146 , a counter  147 , and a temperature detector  148  which constitutes a part of the present invention. The control IC chip  120  further includes a charge control terminal COUT, a discharge control terminal DOUT, a VDD terminal, a VSS terminal, a DS terminal, and a V negative terminal V−. The temperature detector  148  is connected to the first logic circuit  141  and the second logic circuit  142 . The first logic circuit  141  and the second logic circuit  142  are connected to the charge control terminal COUT and the discharge control terminal DOUT, respectively. 
     The temperature detector  148  is configured to utilize a negative temperature characteristic of a diode D 1  illustrated in  FIG. 7A . As shown in  FIG. 6 , the temperature detector  148  includes an inverter  149 , resistance elements R 1  and R 2 , and the diode D 1 . The resistance elements R 1  and R 2  and the diode D 1  are disposed at the input side of the inverter  149 . The inverter  149  has a threshold SH. The threshold SH is set based on a temperature T 1  to be detected and the temperature characteristic of the diode D 1 . The inverter  149  is connected to the first logic circuit  141  and the second logic circuit  142 . 
     When the temperature of the diode D 1  is lower than the predetermined temperature T 1 , an input voltage of the inverter  149  is high, and an output of the inverter  149  is “L”. Outputs of the first logic circuit  141  and the second logic circuit  142  are “H”, and potentials of the charge control terminal COUT and the discharge control terminal DOUT are “H”. 
     As the temperature of the diode D 1  rises, a forward current of the diode D 1  lowers as shown in  FIG. 7A . Accordingly, the input voltage of the inverter  149  lowers as shown in  FIG. 7B . When the temperature exceeds the predetermined temperature T 1 , the input voltage of the inverter  149  falls below the threshold SH. In response, the output of the inverter  149  is inverted into “H”. When the output of the inverter  149  is inverted into “H”, the outputs of the first logic circuit and the second logic circuit  142  are switched to “L”, and the potentials of the charge control terminal COUT and the discharge control terminal DOUT are switched to “L”. Thus, both the first and second FET-SW chips  121  and  122  are turned off. 
     [Battery Protection Device  100 ] 
     Referring back to  FIG. 1 , the battery protection module  110  is mounted on a battery protection module mount section  151  ( FIG. 2 ) of the base printed board  150 . The terminals  101 - 1 ,  102 - 1 ,  103 - 1 , and  105 - 1  disposed at the corners of the battery protection module  110  are soldered to the corresponding terminals  101 - 2 ,  102 - 2 ,  103 - 2 , and  105 - 2  of the base printed board  150 . The connector member  160  is bonded to a connector member mount section  152  ( FIG. 2 ). An end  103   a  of the battery pack negative output terminal  103  and an end  104   a  of the battery pack positive output terminal  104  are connected to the corresponding terminals  103 - 3  and  104 - 1  ( FIG. 2 ). 
     Referring to  FIG. 8 , terminal strips  210  and  211  are connected to the terminals  101  and  102  of the battery protection device  100 , respectively. Referring then to  FIG. 9 , outer ends of the terminal strips  210  and  211  are connected to corresponding electrodes of the lithium-ion battery  201 , so the battery protection device  100  is attached on a side face of the lithium-ion battery  201 . The lithium-ion battery  201  with the battery protection device  100  attached is assembled in cases  212   a  and  212   b . Thus, the battery pack  200  is completed. 
     [Overcurrent of Battery Pack  200 ] 
     When the battery pack  200  of  FIG. 8  is used, the battery pack  200  is attached to a mobile device to be electrically connected to the mobile device through the battery pack negative output terminal  103  and the battery pack positive output terminal  104 . If a voltage of the lithium-ion battery  201  drops to or below a predetermined voltage and therefore the lithium-ion battery  201  is overdischarged, the second FET-SW chip  122  is turned off. If a large current is applied due to some failure such as a short circuit, the first FET-SW chip  122  is turned off. 
     When the battery pack  200  of  FIG. 8  is charged, the battery pack  200  is placed on a recharger to be electrically connected to the recharger through the battery pack negative output terminal  103  and the battery pack positive output terminal  104 . If a large current is applied to the lithium-ion battery  201  due to some failure during charging and therefore the lithium-ion battery  201  is overcharged, the first FET-SW chip  121  is turned off to protect the lithium-ion battery  201 . 
     If a large current is applied between the terminal  101  and the terminal  103  shown in  FIG. 10  and results in an overcurrent, the following operations are also performed. 
     When a large current is applied from the terminal  103  to the terminal  101  during charging, the first and second FET-SW chips  121  and  122  generate heat. The heat of the first and second FET-SW chips  121  and  122  is transferred to the control IC chip  120 . When the temperature detected by the temperature detector  148  exceeds the predetermined temperature, the input voltage of the inverter  149  exceeds the threshold. In response, the output of the inverter  149  is inverted into “H”. The outputs of the first logic circuit and the second logic circuit  142  are switched to “L”, and the potentials of the charge control terminal COUT and the discharge control terminal DOUT are switched to “L”. Thus, both the first and second FET-SW chips  121  and  122  are turned off. A path between the terminal  103  and the terminal  101  is cut in this way, thereby protecting the lithium-ion battery  201  and preventing overheating of the battery protection device  100 . If a large current is applied from the terminal  103  to the terminal  101  during discharging, the same operations are performed to turn off both the first and second FET-SW chips  121  and  122 . This protects the mobile device and prevents overheating of the battery protection device  100 , especially overheating of the first and second FET-SW chips  121  and  122 . 
     Second Embodiment 
     In a second embodiment, the control IC chip  120  and the first and second FET-SW chips  121  and  122  of the first embodiment are integrated into one module. 
       FIG. 11  shows a control IC chip module  300  serving as a battery IC chip module. In the control IC chip module  300 , first and second FET-SW chips  121  and  122  are mounted side-by-side on a board  301  having terminals  302 . A control IC chip  120  is secured onto the adjacent first and second FET-SW chips  121  and  122  with a double-sided adhesive tape so as to extend across the first and second FET-SW chips  121  and  122 . Au wires  126 - 1  through  126 - 5  are provided with their ends bonded. The control IC chip  120 , the first and second FET-SW chips  121  and  122 , and the Au wires  126 - 1  through  126 - 5  are encapsulated by a synthetic resin part  310 . 
     Referring to  FIGS. 12 and 13 , the control IC chip module  300  is mounted on a COB-compatible printed board  111 A together with a resistance chip  123  and a capacitor chip  124 . The resistance chip  123  and the capacitor chip  124  are encapsulated by a synthetic resin part  127 A. In this way, a battery protection module  110 A is formed. 
     In place of the independent first and second FET-SW chips  121  and  122 , a part integrally comprising the first and second FET-SW chips  121  and  122  arranged side-by-side may be used. 
     The present application is based on Japanese Priority Application No. 2005-020213 filed on Jan. 27, 2005, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.