Abstract:
A battery protection IC applied to a battery charging system is provided, where the battery charging system includes a charger and a switch, the switch is coupled between the charger and a battery when the battery is put into the battery charging system, and the battery protection IC includes a voltage divider, a comparator and a controller. The voltage divider is coupled to a first node of the switch, and is utilized for dividing a voltage of the first node to generate a divided voltage, whereat least one resistor of the voltage divider is formed by two different types of fuses. The comparator is utilized for comparing the voltage with a reference voltage to generate a comparison result. The controller is utilized for generating a control signal according to the comparison result, where the control signal is utilized for switching on or switching off the switch.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery protection integrated circuit, and more particularly, to a battery protection integrated circuit that can precisely detect a voltage of a battery and protect the battery from being overcharged or over-discharged. 
     2. Description of the Prior Art 
     When a battery is charged or discharged, a battery protection integrated circuit (IC) is used to detect a voltage of the battery and to prevent the battery from being overcharged or over-discharged. In detail, the battery protection IC has a voltage divider and a comparator, the voltage divider divides a current voltage of the battery to generate a divided voltage, and the comparator compares the divided voltage with a predetermined voltage to generate a comparison result, where the comparison result is used to indicate whether the battery approaches an overcharge or over-discharge threshold. When the comparison result indicates that the battery approaches the overcharge or over-discharge threshold, the battery protection IC stops charging or discharging the battery to prevent the battery from being damaged. 
     However, when the voltage divider is not accurate (i.e., resistances of the resistors of the voltage divider may have error), the divided voltage and the comparison result may not represent the state (voltage) of the battery correctly. Therefore, the battery may be overcharged or over-discharged due to the inaccurate voltage divider, causing the battery damaged. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide a battery protection IC, which has an accurate voltage divider, to solve the above-mentioned problem. 
     According to one embodiment of the present invention, a battery protection integrated circuit applied to a battery charging system is provided, wherein the battery charging system comprises a charger and a switch, the switch is coupled between the charger and a battery when the battery is put into the battery charging system, the switch is utilized for selectively coupling the charger to the battery, and the battery protection integrated circuit comprises a voltage divider, a comparator and a controller. The voltage divider is coupled to a first node of the switch, and is utilized for dividing a voltage of the first node of the switch to generate a divided voltage, where a resistor of the voltage divider are formed by at least a first fuse resistor and a second fuse resistor, the first fuse resistor is one of a laser fuse, an electrical fuse and an anti-fuse, and the second fuse resistor is another one of the laser fuse, electrical fuse and anti-fuse. The comparator is coupled to the voltage divider, and is utilized for comparing the voltage of the first node of the switch with a reference voltage to generate a comparison result. The controller is coupled to the comparator, and is utilized for generating a control signal according to the comparison result, where the control signal is utilized for switching on or switching off the switch. 
     According to another embodiment of the present invention, a battery protection integrated circuit applied to a battery discharging system is provided, where the battery discharging system comprises a load and a switch, the load is connected to a battery when the battery is put into the battery discharging system, the switch is utilized for selectively allowing the battery to discharge, and the battery protection integrated circuit comprises a voltage divider, a comparator and a controller. The voltage divider is coupled to a first node of the switch, and is utilized for dividing a voltage of the first node of the switch to generate a divided voltage, wherein a resistor of the voltage divider are formed by at least a first fuse resistor and a second fuse resistor, the first fuse resistor is one of a laser fuse, an electrical fuse and an anti-fuse, and the second fuse resistor is another one of the laser fuse, electrical fuse and anti-fuse. The comparator is coupled to the voltage divider, and is utilized for comparing the voltage of the first node of the switch with a reference voltage to generate a comparison result. The controller is coupled to the comparator, and is utilized for generating a control signal according to the comparison result, where the control signal is utilized for switching on or switching off the switch. 
     According to another embodiment of the present invention, a method for determining resistances of a voltage divider of a battery protection integrated circuit comprises: performing a first fuse trimming operation upon the resistors of the voltage divider; determining whether the resistances of the resistors of the voltage divider satisfy a rule; and when the resistances of the voltage divider do not satisfy the rule, performing a second fuse trimming operation upon the resistors of the voltage divider, where the first fuse trimming operation is one of a laser fuse trimming operation, an electrical fuse trimming operation and a anti-fuse trimming operation, and the second fuse trimming operation is another one of the laser fuse trimming operation, electrical fuse trimming operation and anti-fuse trimming operation. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a battery charging system according to one embodiment of the present invention. 
         FIG. 2  is a diagram showing that the resistor is formed by the electrical fuse and the laser fuse. 
         FIG. 3  is a flowchart of a method for determining resistances of resistors of a voltage divider of a battery protection IC according to one embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a battery discharging system according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. The terms “couple” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     Please refer to  FIG. 1 , which illustrates a battery charging system  100  according to one embodiment of the present invention. Referring to  FIG. 1 , the battery charging system  100  includes a battery protection IC  110 , a charger  120 , a switch  130 , where the battery protection IC  110  includes a voltage divider  112  including two resistors R 1  and R 2 , a comparator  114  and a controller  116 . In this embodiment, at least one of the resistors R 1  and R 2  is formed by at least a first fuse resistor and a second fuse resistor, where the first fuse resistor is one of a laser fuse, an electrical fuse and an anti-fuse, and the second fuse resistor is another one of the laser fuse, electrical fuse and anti-fuse. 
       FIG. 2  is a diagram showing that the resistor R 1  or R 1  is formed by the laser fuse and the electrical fuse. As shown in  FIG. 2 , the resistance of the resistor R 1  or R 2  is determined by the laser fuse  206  and the electrical fuse  204 . The laser fuse  206  means that one or more fuses are cut by a laser trimming operation to have a required resistance, and the electrical fuse  204  means that one or more fuses are cut by inputting an over-current from the internal pads  202  to have a required resistance. Because the functions of the laser fuse  206  and the electrical fuse  204  should be known by a person skilled in this art, further descriptions are therefore omitted here. 
     Please refer to  FIGS. 1-3  together,  FIG. 3  is a flowchart of a method for determining resistances of the resistors R 1  and R 2  of the voltage divider  112  of the battery protection IC  110  according to one embodiment of the present invention. Referring to  FIG. 3 , the flow is described as follows: 
     In Step  300 , the flow starts. In Step  302 , a laser fuse trimming operation is performed upon the resistors R 1  and R 2  of the voltage divider  112 . In Step  304 , it is determined whether the resistances of the resistors R 1  and R 2  of the voltage divider  112  satisfy a rule (i.e., determining whether the resistances of the resistors R 1  and R 2  are accurate). For example, assuming that the charge threshold of the battery is 4.2V, an engineer can input a test voltage (4.2V±20 mV) into the voltage divider  112  to determine whether the switch  130  is switched off or not. If the switch  130  is switched off, it is meant that the resistances of the resistors R 1  and R 2  are accurate; and if the switch  130  is still switched on, it is meant that the resistances of the resistors R 1  and R 2  are not accurate. In this embodiment, if the switch  130  is still switched on when the engineer inputs the test voltage (4.2V±20 mV), the engineer can input other test voltages into the voltage divider  112  to determine a minimum test voltage higher than (4.2V+20 mV) or a maximum test voltage lower than (4.2V-20 mV) that can make the switch  130  switched off. 
     When it is determined that the resistors R 1  and R 2  of the voltage divider  112  satisfy the rule, the flow enters Step  308  to finish the flow; and when it is determined that the resistors R 1  and R 2  of the voltage divider  112  do not satisfy the rule, the flow enters Step  306 . In Step  306 , an electrical fuse trimming operation is performed upon the resistors R 1  and R 2  of the voltage divider  112  by referring to a look-up table to adjust the resistances of the resistors R 1  and R 2 , where the look-up table here records minimum/maximum test voltages that can switch off the switch  130  and their corresponding electrical fuse trimming operations. Then, the flow enters Step  308  to finish the flow. 
     It is noted that although the embodiment shown in  FIG. 2  and  FIG. 3  shows the resistors R 1  and R 2  are formed by the laser fuse and the electrical fuse, it is not meant to be a limitation of the present invention. In other embodiments of the present invention, the resistors R 1  and R 2  can be formed by any two of the laser fuse, electrical fuse and anti-fuse. These alternative designs should fall within the scope of the present invention. 
     After the resistances of the resistors of the voltage divider  112  is precisely adjusted, the battery charging system  100  can be operated correctly. In the operations of the battery charging system  100 , at the beginning, the switch  130  is switched on, a battery  140  is put into the battery charging system  100 , and the charger  120  starts to charge the battery  140 . Then, the voltage divider  112  divides the current voltage V bat  of the battery  140  to generate a divided voltage V div , and the comparator  114  compares the divided voltage V div  with a reference voltage V ref  to generate a comparison result V cr , where the comparison result V cr  is used to indicate whether the battery  140  approaches an overcharge threshold. Then, the controller  116  receives the comparison result V cr , and generates a control signal V SW  according to the comparison result V cr , where the control signal V SW  is used to switch on or switch off the switch  130 . In detail, when the divided voltage V div  is greater than the reference voltage V ref , it is meant that the voltage V bat  approaches the overcharge threshold (in this embodiment, “approach the overcharge threshold” can be determined by detect whether the voltage V bat  is greater than 4.2 volts), and the controller  116  generates the control signal V SW  to switch off the switch  130  to prevent the battery  140  from being charged by the charger  120 . On the other hand, when the divided voltage V div  is not greater than the reference voltage V ref , it is meant that the voltage V bat  does not approach the overcharge threshold (in the safe region), and switch  130  is switched on to make the charger  120  continue charging the battery  140 . 
     Please refer to  FIG. 4 , which illustrates a battery discharging system  400  according to one embodiment of the present invention. Referring to  FIG. 4 , the battery discharging system  4100  includes a battery protection IC  410 , a load  420 , a switch  430 , where the battery protection IC  410  includes a voltage divider  412  including two resistors R 1  and R 2 , a comparator  414  and a controller  416 . In this embodiment, at least one of the resistors R 1  and R 2  is formed by at least a first fuse resistor and a second fuse resistor, where the first fuse resistor is one of a laser fuse, an electrical fuse and an anti-fuse, and the second fuse resistor is another one of the laser fuse, electrical fuse and anti-fuse. 
     Furthermore, the determination of the resistances of the resistors R 1  and R 2  of the voltage divider  412  is the same as the determination of that of the voltage divider  112  shown in  FIG. 1 . That is, the determination of the resistances of the resistors R 1  and R 2  of the voltage divider  412  can refer to  FIG. 2  and  FIG. 3  and above-mentioned disclosure. 
     In the operations of the battery discharging system  400 , at the beginning, the switch  430  is switched on, a battery  440  is put into the battery discharging system  400 , and battery  440  begins to be discharged. Then, the voltage divider  412  divides the current voltage V bat  of the battery  440  to generate a divided voltage V div , and the comparator  414  compares the divided voltage V div  with a reference voltage V ref  to generate a comparison result V cr , where the comparison result V cr  is used to indicate whether the battery  440  approaches an over-discharge threshold. Then, the controller  416  receives the comparison result V cr , and generates a control signal V SW  according to the comparison result V cr , where the control signal V SW  is used to switch on or switch off the switch  430 . In detail, when the divided voltage V div  is greater than the reference voltage V ref , it is meant that the voltage V bat  does not approach the over-discharge threshold (in this embodiment, “approach the over-discharge threshold” can be determined by detect whether the voltage V bat  is lower than 3.8 volts), and the controller  416  generates the control signal V SW  to switch on the switch  430  to continue discharge the battery  440 . On the other hand, when the divided voltage V div  is not greater than the reference voltage V ref , it is meant that the voltage V bat  approaches the over-discharge threshold, and the controller  416  generates the control signal V SW  to switch off the switch  430  to prevent the battery from being over-discharged. 
     Briefly summarized, in the battery protection IC of the present invention, at least one of the resistors of the voltage divider is formed by two different types of fuses. Therefore, the resistances of the resistors of the voltage divider can be determined accurately, and the battery protection IC can function well. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.