Abstract:
An overstress protection apparatus includes a switch detector. The switch is arranged in a grounding path of a load system. The detector detects the current, voltage or temperature of the load system to determine a signal for controlling the switch, to thereby protect the load system working in normal conditions.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related generally to an overstress protection apparatus and method. 
       BACKGROUND OF THE INVENTION 
       [0002]    The various chips on a circuit board operate with different voltages and are therefore designed according to their respective voltage tolerance levels. In normal operating conditions, circuits with different operating voltages are separated from each other. Nonetheless, in practice, it is possible for a short circuit being established between the pins of circuits with different operating voltages, for example, because of accumulation of dust, or intrusion of an electrically conductive substance such as water or metal. Given an ordinary design framework without any protection apparatus, a short circuit between the pins of circuits with different operating voltages is likely to subject a chip to overcurrent and hence excessive power consumption. As a result, the overloaded chip heats up quickly and may burn out or even catch fire, thereby posing a safety issue. 
         [0003]    U.S. Pat. No. 6,829,129 connects each of alternating current (AC) power supplies with a fuse in series thereto, and each two of the power supplies with a metal oxide varistor therebetween. The metal oxide varistor or the fuse will burn out under abnormal circuit conditions to break and thereby protect the circuit. In practice, however, the metal oxide varistor and the fuse are not very reliable, sometimes burnout resistant, and therefore may not be effective in protecting a circuit. 
         [0004]    U.S. Pat. No. 7,274,543 connects an overvoltage protection circuit to an I/O pin of a chip to identify whether or not the voltage at the I/O pin is within a normal operating range and accordingly, to control a high-breakdown-voltage MOS transistor to disconnect the chip from the power supply of unduly high voltage. However, as a short circuit may occur at each of the I/O pins of a chip, it is necessary to provide each of the I/O pins with an overvoltage protection circuit, and the overvoltage protection circuits will take up much space. 
         [0005]    U.S. Pat. No. 7,253,505 connects a layer of variable-resistance material between a ground terminal and a ground layer of a chip. When a surge pulse occurs, the energy of the surge pulse will flow through the variable-resistance material. Due to the nature of the variable-resistance material, the energy of the surge pulse will be released evenly to the ground lines, and the chip is thus protected from damage. This solution works only with a specific manufacturing process and therefore does not apply to all types of chips. More badly, with the layer of variable-resistance material disposed on the ground layer, an increase in current is always accompanied a reduction in voltage, and hence it is not applicable to chips which operate with high current. 
         [0006]    Therefore, it is desired a simple-structure, widely applicable, and small-size overstress protection apparatus. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide an overstress protection apparatus and method. 
         [0008]    Another object of the present invention is to provide a small-size overstress protection apparatus. 
         [0009]    According to the present invention, an overstress protection apparatus includes a switch and a detector. The switch is in a grounding path of a load system, and the detector detects the current, voltage or temperature of the load system to determine a signal for controlling the switch. 
         [0010]    According to the present invention, an overstress protection method includes detecting the current, voltage or temperature of a load system to determine a signal, and switching a switch between the load system and a ground terminal by the signal. 
         [0011]    Preferably, a resistor is further included to establish a current path between the load system and the ground terminal during the switch is off. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a circuit diagram of a first embodiment according to the present invention; 
           [0014]      FIG. 2  is a circuit diagram of a second embodiment according to the present invention; 
           [0015]      FIG. 3  is a circuit diagram of a third embodiment according to the present invention; 
           [0016]      FIG. 4  is a circuit diagram of a fourth embodiment according to the present invention; 
           [0017]      FIG. 5  is a circuit diagram of a fifth embodiment according to the present invention; 
           [0018]      FIG. 6  is a circuit diagram of a sixth embodiment according to the present invention; 
           [0019]      FIG. 7  is a circuit diagram of a seventh embodiment according to the present invention; 
           [0020]      FIG. 8  is a circuit diagram of an eighth embodiment according to the present invention; 
           [0021]      FIG. 9  is a circuit diagram of a ninth embodiment according to the present invention; and 
           [0022]      FIG. 10  is a circuit diagram of a tenth embodiment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  is a circuit diagram of a first embodiment according to the present invention, in which load systems  10  and  12  are circuit systems operating with an input voltage LV, and an overstress protection apparatus  20  is operative to protect the load systems  10  and  12 . The overstress protection apparatus  20  includes switches SW 1  and SW 2  and an overcurrent detector  22 . The switches SW 1  and SW 2  are connected between a ground terminal GND and load terminals A_GND and B_GND, respectively. The overcurrent detector  22  detects the voltage at the load terminals A_GND and B_GND to detect the current flowing through the switches SW 1  and SW 2 , and thereby determines an overcurrent signal Socp for controlling the switches SW 1  and SW 2 . In normal operation, the voltage at the power supply terminal LV is a low voltage and detected by the overcurrent detector  22 , the currents flowing through the load terminals A_GND and B_GND will be within preset ranges. Therefore, the overcurrent signal Socp will turn on the switches SW 1  and SW 2  and thus allows the currents flowing through the switches SW 1  and SW 2 . However, if a short circuit happens between the power supply terminal LV and any other power supply terminal receiving a higher voltage so that the overcurrent detector  22  detects the currents flowing through the load terminals A_GND and B_GND over its preset range, the overcurrent signal Socp will be changed to turn off the switches SW 1  and SW 2 . In consequence, the grounding paths of the load systems  10  and  12  are cut off to stop the load systems  10  and  12  from operation. 
         [0024]      FIG. 2  is a circuit diagram of a second embodiment according to the present invention, in which an overstress protection apparatus  24  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  24 , MOSes Q 1  and Q 2  are connected between the ground terminal GND and the load terminals A_GND and B_GND, respectively, and are connected with resistors R 1  and R 2  in parallel, respectively, and an overcurrent detector  26  includes an output terminal  28  for providing an overcurrent signal Socp to control the MOSes Q 1  and Q 2 , a resistor R 3  connected between the power supply terminal LV and the output terminal  28 , and a MOS Qc connected between the output terminal  28  and the ground terminal GND to be controlled by the voltages at the load terminals A_GND and B_GND. In normal operation, the voltage at the power supply terminal LV is a low voltage, and thus the currents flowing through the load terminals A_GND and B_GND are both low. As a result, the voltages of the MOSes Q 1  and Q 2  are lower, and the voltages at the load terminals A_GND and B_GND are insufficient to turn on the MOS Qc. Hence, the overcurrent signal Socp is high and turns on the MOSes Q 1  and Q 2 . However, if a short circuit happens between the, power supply terminal LV and any other power supply terminal receiving a higher voltage, the currents flowing through the load terminals A_GND and B_GND will increase, and so will the voltages of the MOSes Q 1  and Q 2 . As a result, the voltages at the load terminals A_GND and B_GND rise, thereby turning on the MOS Qc, while the overcurrent signal Socp becomes low, thereby turning off the MOSes Q 1  and Q 2 . The currents of the load systems  10  and  12  will flow to the ground terminal GND through the resistors R 1  and R 2 , respectively, and thereby establish a great voltage drop to pull high the electrical potential of the load systems  10  and  12 , as well as to increase the resistance between the power supply terminal LV and the ground terminal GND to result in a reduced total current. Ultimately, the voltage across the load systems  10  and  12  is maintained within a normal range to protect the load systems  10  and  12 . 
         [0025]      FIG. 3  is a circuit diagram of a third embodiment according to the present invention, in which an overstress protection apparatus  30  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  30 , MOSes Q 1 , Q 2  and resistors R 1 , R 2  are all the same as that of the embodiment shown in  FIG. 2 . However, an overcurrent detector  32  includes a resistor R 3  and a capacitor C 1  serially connected between a power supply terminal LV and a ground terminal GND, a MOS Qc connected with the capacitor C 1  in parallel, a switch SW 3  and a resistor R 4  connected between the power supply terminal LV and the ground terminal GND, an inverter  36  connected between the capacitor C 1  and the switch SW 3 , and an output terminal  34  for providing an overcurrent signal Socp to control the MOSes Q 1  and Q 2 . In normal operation, the voltage at the power supply terminal LV is a low voltage, and the currents flowing through the load terminals A_GND and B_GND are both low. As a result, the voltages of the MOSes Q 1  and Q 2  are lower, and the voltages at the load terminals A_GND and B_GND are insufficient to turn on the MOS Qc. Hence, the capacitor C 1  is charged by a current IR 3  flowing through the resistor R 3  such that a low-level signal Si is generated to turn on the switch SW 3 , and the overcurrent signal Socp is high and thus turns on the MOSes Q 1  and Q 2 . If a short circuit happens between the power supply terminal LV and any other power supply terminal receiving a higher voltage, the currents flowing through the load terminals A_GND and B_GND will increase, and so will the voltages of the MOSes Q 1  and Q 2 . As a result, the voltages at the load terminals A_GND and B_GND turn on the MOS Qc, and the capacitor C 1  is discharged such that a high-level signal Si is generated to turn off the switch SW 3 . Consequently, the overcurrent signal Socp becomes low and thus turns off the MOSes Q 1  and Q 2 . The currents of the load systems  10  and  12  will flow to the ground terminal GND through the resistors R 1  and R 2 , respectively, thereby pulling high the voltages at the load terminals A_GND and B_GND to protect the load systems  10  and  12 . 
         [0026]    Replacing the MOSes Q 1  and Q 2  shown in  FIG. 3  by bipolar junction transistors (BJTs) Q 3  and Q 4  turns the third embodiment into a fourth embodiment as shown in  FIG. 4 , in which an overstress protection apparatus  38  operates in the same way as the overstress protection apparatus  30  shown in  FIG. 3 . 
         [0027]      FIG. 5  is a circuit diagram of a fifth embodiment according to the present invention, in which an overstress protection apparatus  40  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  40 , switches SW 1  and SW 2  are connected between load terminals  44  and  46  and a ground terminal GND, respectively, and an overvoltage detector  42  is connected to a power supply terminal LV to detect the voltage thereof to determine an overvoltage signal Sovp for controlling the switches SW 1  and SW 2 . In normal operation, the voltage at the power supply terminal LV is a low voltage and is identified within a preset range by the overvoltage detector  42 , and the overvoltage signal Sovp turns on the switches SW 1  and SW 2 . However, if a short circuit happens between the power supply terminal LV and any other power supply terminal receiving a higher voltage such that the voltage at the power supply terminal LV is detected over the preset range by the overvoltage detector  42 , the overvoltage signal Sovp will turn off the switches SW 1  and SW 2 . In consequence, the grounding paths of the load systems  10  and  12  are cut off to stop the load systems  10  and  12  from operation. 
         [0028]      FIG. 6  is a circuit diagram of a sixth embodiment according to the present invention, in which an overstress protection apparatus  48  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  48 , MOSes Q 1  and Q 2  are connected between the load terminals  44 ,  46  and a ground terminal GND, respectively, and connected with resistors R 1 , R 2  in parallel, respectively, and an overvoltage detector  42  is connected to the power supply terminal LV to provide an overvoltage signal Sovp for controlling the MOSes Q 1  and Q 2 . If the overvoltage detector  42  detects the voltage at the power supply terminal LV within a preset range, the overvoltage signal Sovp will turn on the MOSes Q 1  and Q 2 . If a short circuit happens between the power supply terminal LV and any other power supply terminal receiving a higher voltage such that the overvoltage detector  42  detects the voltage at the power supply terminal LV over the preset range, the overvoltage signal Sovp will turn off the MOSes Q 1  and Q 2 . The currents of the load systems  10  and  12  will flow to the resistors R 1  and R 2 , respectively, to pull high the voltages at the load terminals  44  and  46  to protect the load systems  10  and  12 . 
         [0029]    Replacing the MOSes Q 1  and Q 2  shown in  FIG. 6  by BJTs Q 3  and Q 4  turns the sixth embodiment into a seventh embodiment as shown in  FIG. 7 , in which an overstress protection apparatus  50  operates in the same way as the overstress protection apparatus  48  shown in  FIG. 6 . 
         [0030]      FIG. 8  is a circuit diagram of an eighth embodiment according to the present invention, in which an overstress protection apparatus  52  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  52 , switches SW 1 , SW 2  are connected between load terminals  56 ,  58  and the ground terminal GND, respectively, an overtemperature detector  54  detects the temperatures of the load systems  10  and  12  to determine an overtemperature signal Sotp for controlling the switches SW 1  and SW 2 . If a short circuit happens between a power supply terminal LV and any other power supply terminal receiving a higher voltage, a large current will be generated to cause the temperatures of the load systems  10  and  12  to rise. Once the overtemperature detector  54  detects an abnormal temperature of the load systems  10  and  12 , the overtemperature signal Sotp will turn off the switches SW 1  and SW 2 . As a result, the grounding paths of the load systems  10  and  12  are cut off to stop the load systems  10 ,  12  from operation. 
         [0031]      FIG. 9  is a circuit diagram of a ninth embodiment according to the present invention, in which an overstress protection apparatus  60  is operative to protect load systems  10  and  12 . In the overstress protection apparatus  60 , MOSes Q 1  and Q 2  are connected between the ground terminal GND and load terminals  56 ,  58 , respectively, and connected with resistors R 1 , R 2  in parallel, respectively. The overtemperature detector  54  detects the temperature of the load systems  10  and  12  to determine an overtemperature signal Sotp applied to the gates of the MOSes Q 1  and Q 2 . When the load systems  10  and  12  operate at normal temperature, the overtemperature signal Sotp turns on the MOSes Q 1  and Q 2 . If a short circuit happens between the power supply terminal LV and any other power supply terminal receiving a higher voltage, the load systems  10  and  12  will be overheated due to overloaded. Once the temperature of the load systems  10  and  12  are detected over a preset range, the overtemperature signal Sotp will turn off the MOSes Q 1  and Q 2 . The currents of the load systems  10  and  12  will flow to the ground terminal GND through the resistors R 1  and R 2 , respectively, thereby pulling high the voltages at the load terminals  56  and  58  to protect the load systems  10  and  12 . 
         [0032]    Replacing the MOSes Q 1  and Q 2  shown in  FIG. 9  by BJTs Q 3  and Q 4  turns the ninth embodiment into a tenth embodiment as shown in  FIG. 10 , in which an overstress protection apparatus  62  operates in the same way as the overstress protection apparatus  60  shown in  FIG. 9 . 
         [0033]    While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims. cm What is claimed is: