Abstract:
The purpose of the present invention is to provide an electronic control device including an integratable protection circuit that is capable of protecting an internal circuit, a sensor, etc., against both of surge voltage application and battery connection abnormality. The electronic control device includes an input terminal connectable to an external sensor and switch, and a power supply wiring and a GND wiring that are utilized to supply power to the internal circuit, wherein protection elements each including a PN junction are connected between the input terminal and the power supply wiring or the GND wiring, and protection resistor are further connected in series between the protection elements and the power supply wiring or the GND wiring.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electronic control device which controls an engine or the like of an automobile, and in particular, to an electronic control device provided with the protection means for protecting an internal circuit, the sensors or the like from a surge or battery connection abnormality, with regard to a path of a signal inputted into the electronic control device from various kinds of sensors or operation switches (hereinafter referred to as sensor(s) or the like) mounted on a controlled object. 
       BACKGROUND ART 
       [0002]    In recent years, high performance of an automobile is remarkable, and accordingly the number of electronic control devices mounted on a vehicle is increasing. Meanwhile, the space which can be allotted to an electronic control device is decreasing for improving fuel economy by a weight reduction, and securing the interior space. The demand for reducing the size of the electronic control device has become strong. 
         [0003]    For methods of miniaturizing the electronic control device, one effective way is to integrate elements mounted on a printed circuit board as individual elements into an integrated circuit (IC). Since, in particular, a protection circuit with above-mentioned resistors and capacitors has tens of input terminals and each of the terminals is to be mounted on the circuit, a considerable printed circuit board area is needed for the mounting. Thus, the miniaturization effect by integrating the circuit is large. 
         [0004]    However, in cases where this protection circuit is integrated, there is the problem that integration of capacitors is difficult due to the following reasons. That is, the capacitors used for the above-mentioned conventional protection circuit need a capacitance value (for example, several dozens of nF to several hundreds of nF) that is equal to or larger than a certain value in order to absorb surge energy. However, in order to achieve such a capacitor of large capacity within an IC, a very large chip area is needed, and the large capacitor is not well suited in cost as compared with the merit of the miniaturization by integration. 
         [0005]    A known protection circuit coping with this problem is, for example, a protection circuit which has a diode between an input terminal and a power supply/GND as shown in the FIG. 8 of PTL 1. Use of the diode in the protection circuit allows the circuit itself not to absorb surge energy, but allows the surge energy to be released to a power supply/GND, and surge energy withstand needed for the diode itself can be suppressed. Since the surge energy withstand of an element is generally proportional to the area of a chip, the chip area needed for a protection circuit can be suppressed, and thus cost can be suppressed. 
         [0006]    As a similar configuration, the method of using a ggMOS (grounded gate metal oxide semiconductor transistor) or a thyristor structure instead of the diode is also generally used. Common for a protection circuit using these elements including diodes is that the protection circuit operates such that normally, the PN junction in each element is reversely biased, and when a surge is applied, the PN junction is forward biased, or the MOS structure or the thyristor structure is turned on and thus the surge is released to a power supply or GND, or is absorbed. 
         [0007]    Although these protection circuit methods are effective against a surge application, they cannot cope with the negative voltage application due to battery connection abnormality. That is, if a Vb power supply with reversed polarity is applied to an input terminal through the sensors or the like, it is not possible to prevent large current from flowing into the input terminal from the GND. 
       CITATION LIST 
     Patent Literature 
       [0008]    PTL 1: JP 2013-3072076 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    The object of the present invention is to provide an electronic control device including a protection circuit that can be integrated and is capable of protecting an internal circuit, and sensors or the like against both surge application and battery connection abnormality. 
       Solution to Problem 
       [0010]    An electronic control device includes: an input terminal connectable with an external sensor or an external switch; and a power supply wiring and a GND wiring used for supplying power to an internal circuit, wherein a protection element including a PN junction is connected between the input terminal and the power supply wiring or the GND wiring, and a protection resistor is further connected in series between the protection element and the power supply wiring or the GND wiring. 
       Advantageous Effects of Invention 
       [0011]    According to the present invention, an electronic control device including a protection circuit that can be integrated and is capable of protecting an internal circuit, and the sensors or the like against both surge application and battery connection abnormality can be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a circuit block diagram showing a general circuit configuration of an electronic control device, and sensors or the like. 
           [0013]      FIG. 2  is a diagram showing influence when a surge is applied to the electronic control device shown in  FIG. 1 . 
           [0014]      FIG. 3  is a diagram showing influence of battery connection abnormality occurring in the electronic control device shown in  FIG. 1 . 
           [0015]      FIG. 4  is a circuit block diagram showing an example of a configuration of a protection circuit used in a conventional electronic control device. 
           [0016]      FIG. 5  is a circuit block diagram showing a configuration when a conventional integrated protection circuit is applied to an electronic control device. 
           [0017]      FIG. 6  is a circuit block diagram showing a configuration of an electronic control device  1  according to a first embodiment. 
           [0018]      FIG. 7  is a diagram showing an example of surge application conditions due to static electricity. 
           [0019]      FIG. 8  is a view showing a section structure of an integrated protection circuit  41  in a mounting method in the first embodiment. 
           [0020]      FIG. 9  is a view showing a section structure of an integrated protection circuit  41  in a mounting method in the first embodiment. 
           [0021]      FIG. 10  is a circuit block diagram showing a configuration of the electronic control device  1  according to a second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    [Outline of Electronic Control Device] 
         [0023]    Conventionally, as means to highly control an engine of a car or the like, an electronic control device is used which achieves a desired control of a state of a controlled object such as engine or the like from various sensors or the like connected to the controlled object, such that an operation by a drive is inputted from an operation switch, and an actuator and the like which are mounted in the controlled object are operated according to calculated results by calculating means such as internal microcomputers and the like. 
         [0024]    Such an electronic control device is provided with an input terminal, and the above mentioned sensors or the like are connected to this input terminal, and a predetermined signal is inputted. A general connection configuration of an electronic control device and the sensors or the like is shown in  FIG. 1 . Although  FIG. 1  shows only one of the sensors or the like, and one corresponding input terminal due to space limitation, combinations of tens of sensors or the like and input terminals are practically mounted. 
         [0025]    Generally, an electronic control device is configured such that a wiring (hereinafter referred to as Vb power supply) connected to positive potential of a battery (in many cases, lead battery of nominally 12 V) as the power supply and a wiring (hereinafter referred to as GND) connected to negative potential are connected, and an internal circuit operates by an low voltage internal power supply generated through an internal power supply circuit. While some of the sensors or the like operate by the internal power supply of the electronic control device (not shown), others, as illustrated in  FIG. 1 , are connected to the Vb power supply without using the electronic control device, and operate. 
         [0026]    [Abnormal Input Applied to Electronic Control Device] 
         [0027]    The above is an outline about the electronic control device. Not only the predetermined signal but also an abnormal input is sometimes applied to this input terminal. Although various cases can be considered as this abnormal input, surge application ( FIG. 2 ) and battery connection abnormality ( FIG. 3 ) are mainly listed. 
         [0028]    [Surge Application and its Influence] 
         [0029]    Surge application is an application of static electricity received from a human body and the like at the time of a vehicle assembly, maintenance and the like, impulse surge received from a nearby apparatus or the like through electromagnetic coupling and/or capacitive coupling at the time of operation and the like. Hereinafter, these are collectively referred to as “surge.” 
         [0030]    Meanwhile, inside an electronic control device, a circuit (hereinafter referred to as internal circuit) which is manufactured by micro processing technology and is not highly resistant to a surge as well as a microcomputer are used. If such an internal circuit is connected with the input terminal of the electronic control device directly, the internal circuit may be destroyed by the surge and a correct operation may not be possible. 
         [0031]    [Surge Protection by Protection Circuit] 
         [0032]    In order to prevent this, it is common to have a protection circuit between the input/output terminal and the internal circuit. Even if the surge is applied to the input/output terminal, the protection circuit can prevent the internal circuit from being influenced, since, as shown in  FIG. 2 , the protection circuit allows the surge to be released to a power supply or GND or absorbs the surge. 
         [0033]    [Battery Connection Abnormality and its Influence] 
         [0034]    Battery connection abnormality refers to a connection abnormality in which, for example, the battery used for a Vb power supply is connected reversely with respect to polarity at the time of maintenance and the like. In cases where such a connection abnormality arises, the Vb power supply serves as reversed polarity (negative voltage) relative to GND, and an unusual current tends to flow toward the Vb power supply from GND. 
         [0035]    Various paths can be conceived for the path of this unusual current, as shown in  FIG. 3 . Generally, the unusual current in the path which passes through a power supply circuit is coped with so that it may be cut off within a power supply circuit, but it is necessary to take separate measures for the unusual current in the path which passes via an input terminal. In cases where the unusual current of the path which passes via the input terminal is not cut off, there is a possibility that the sensors or the like connected may be destroyed by large current. Even if the sensors or the like are not destroyed, when the protection circuit itself has been destroyed by burning or the like, protection will not be possible against the surge to be applied in another occasion. 
         [0036]    [Battery Connection Abnormality Protection by Protection Circuit] 
         [0037]    In order to prevent battery connection abnormality, the above-mentioned protection circuit is generally provided with a function which cuts off the unusual current which passes via this input terminal. That is, even if the Vb power supply with reversed polarity is applied to an input/output terminal, since the protection circuit cuts off large current, influence on the sensors or the like connected can be prevented. 
         [0038]    [Conventional Protection Circuit] 
         [0039]    The above protection circuit is achievable by various methods. Conventionally, for example, the protection circuit using a resistor and two capacitors as shown in  FIG. 4  has been used. This protection circuit absorbs the energy of surge by capacitors C 1  and C 2  when a surge is applied, and in the case of battery connection abnormality, R 1  has a function which cuts off the unusual current from an internal circuit to an input terminal, and thus, the internal circuit, and the sensor or the like can be protected from a surge or battery connection abnormality by this protection circuit. Generally, these resistors and capacitors are mounted on a printed circuit board as individual elements.  FIG. 5  is a circuit block diagram showing a configuration when a conventional integrated protection circuit is applied to an electronic control device. Hereinafter, embodiments according to the present invention are described with reference to drawings. 
       First Embodiment 
       [0040]    Hereinafter, an electronic control device according to the first embodiment of the present invention will be described with reference to  FIG. 6 .  FIG. 6  is a circuit block diagram showing a configuration of an electronic control device  1  according to the first embodiment. 
         [0041]    [Configuration of Electronic Control Device  1 ] 
         [0042]    In the electronic control device  1 , a sensor or the like  2  is connected to an input terminal  81  through an input wiring  91 , a positive electrode of a battery  3  is connected to a Vb power supply terminal  82  through a Vb power supply wiring  92 , and a negative electrode of the battery  3  is connected to a GND terminal  83  through a GND wiring  93 . The electronic control device  1  includes a protection circuit  4 , an internal circuit  5 , a power supply circuit  6 , and an output circuit (not shown). The sensor or the like is connected to the Vb power supply wiring  92 , the GND wiring  93 , and the input wiring  91 . 
         [0043]    Protection circuit  4  includes diodes D 1  and D 2 , protection resistors R 1  and R 2 , and capacitors C 1  and C 2 . The diode D 1  and the protection resistor R 1  are disposed in series between the input terminal  81  and an internal power supply  94 . The diode D 2  and the protection resistor R 2  are disposed in series between the input terminal  81  and the GND wiring  93 . A capacitor C 1  is provided between a wiring  95  disposed between the diode D 1  and the protection resistor R 1 , and the GND wiring  93 . A capacitor C 2  is provided between a wiring  96  disposed between the diode D 2  and the protection resistor R 2 , and the GND wiring  93 . The part surrounded by a broken line  49  is a part integrated in the integrated circuit (described later). 
         [0044]    The internal circuit  5  includes a microcomputer and the like, and is connected to the input terminal  91 , the internal power supply  94 , the GND wiring  93 , and an output circuit (not shown) . The power supply circuit  6  is connected to the Vb power supply wiring  92 , the GND wiring  93 , and the internal power supply  94 . The output circuit (not shown) is connected to an actuator (not shown) through the output terminal (not shown). 
         [0045]    [Operation at the Time of Normal Operation] 
         [0046]    First, the operation of the electronic control device  1  and the protection circuit  4  at the time of normal operation is described. As described in the “Background Art”, the role of the electronic control device  1  is to perform control calculation according to the state of the controlled object (not shown), and the input from a driver, and to achieve desired control through the actuator (not shown). In order to achieve this, the electronic control device  1  and the like performs the following operations. 
         [0047]    The sensor or the like  2  outputs the signal according to the input from the state of a controlled object and a driver to the input wiring  91 . The internal circuit  5  reads the signal from the input wiring  91  through the input terminal  81 , carries out control calculation with an internal microcomputer or the like, drives the actuator through the output circuit (not shown), and performs desired control. In addition, the power supply circuit  6  generates, from the Vb power supply of the comparatively high voltage (around 14 [V]) obtained from Vb power supply wiring  92 , the internal power supply of voltage (5 [V], 3.3 [V], etc.) suitable for operation of the internal circuit, and supplies electric power to the internal power supply wiring  94 . 
         [0048]    Here, protection circuit  4  does not perform a positive operation, but passes the signal from the input terminal  81 , and transmits it to the internal circuit S. This is because the protection circuit  4  does not interfere in the input signal in the normal state, and it is required to operate only in the case of abnormality to be described later to perform the protection operation. 
         [0049]    Specifically, since the potential Vin of the input wiring  91  is between a GND potential and a potential Vcc of the internal power supply, the diodes D 1  and D 2  are reversely biased, and current does not flow during the normal operation. At the time of power turn-on, the capacitor C 1  is charged/discharged to a potential Vcc of the internal power supply through the protection resistor R 1 , and the capacitor C 2  is charged/discharged to a GND potential through the protection resistor R 2 . After the charge and discharge are completed, the state is stabilized, and current does not flow. 
         [0050]    [Surge Applied to Electronic Control Device] 
         [0051]    As described in the “Background Art”, the applied surge includes static electricity received from a human body and the like, and impulse surge received from a nearby apparatus or the like through electromagnetic coupling and/or capacitive coupling, and has features in that although it is high voltage, but the duration is short, and the impedance of a surge source is comparatively high. 
         [0052]    For example, in ISO 10605, which is an electrostatic test standard for automotive equipment, one of the static-electricity-application conditions which onboard equipment should bear is that the electric charge of a storage capacitor Cs with a capacity of 330 [pF] charged at ±8 [kV] is applied to the input wiring  91  or the input terminal  81  through discharging resistance Rs of resistance 2 [kΩ].  FIG. 7  shows the relationship between the surge source  7  and the electronic control device  1 . 
         [0053]    In cases where such a surge is applied, the protection circuit  4  in the electronic control device  1  protects the internal circuit  5  by releasing the surge to the internal power supply wiring  94  or the GND wiring  93 . Since the operation at this time differs between when a surge of a positive voltage is applied and when a surge of a negative voltage is applied, each of them will be described below. 
         [0054]    [Operation of Protection Circuit  4  when Positive Voltage Surge is Applied] 
         [0055]    When the surge of a positive voltage is applied to the input terminal  81 , a potential Vin of the input wiring  91  becomes nigher than a potential Vcc of the internal power supply, the diode D 1  is biased in the forward direction, surge current flows in the forward direction, and this surge current flows into the capacitor C 1 . 
         [0056]    At this time, the potential Vin of the input wiring  91  is limited to the voltage obtained by adding the forward voltage Vf 1  of the diode D 1  to the voltage Vc 1  of the capacitor C 1 . Since forward voltage Vf 1  of the diode D 1  can be generally kept less than several tens of volts, and the voltage of Vc 1  of the capacitor C 1  can also be suppressed by sufficiently increasing a capacity of the capacitor C 1 , it is possible to suppress the voltage Vin of the input wiring  91  to a voltage lower than the charge voltages of the storagae capacitor Cs of the surge source  7 , and the internal circuit  5  can be protected. 
         [0057]    Since the surge is not always applied only once, it is necessary to promptly discharge the charge of the capacitor C 1  charged by the surge. This is achieved by being discharged to the wiring  94  of the internal power supply through the protection resistor R 1 . 
         [0058]    [Operation of Protection Circuit  4  when Negative Voltages Surge is Applied] 
         [0059]    In cases where the surge of negative voltage is applied to the input terminal  81 , a potential Vin of the input wiring  91  becomes lower than a GND potential, the diode D 2  is biased in the forward direction, surge current flows in the forward direction, and this surge current flows out of the capacitor C 2 . 
         [0060]    At this time, the potential Vin of the input wiring  91  is limited to the voltage obtained by adding the forward voltage Vf 2  of the diode D 2  to the voltage Vc 2  of the capacitor C 2 . As a result, as with the application of the positive voltage surge, it is possible to suppress the voltage Vin of the input wiring  91  to a voltage lower than the charge voltage of storage capacitor Cs of the surge source  7 , and the internal circuit  5  can be protected. The electric charge of the capacitor C 2  charged by the surge is discharged by the GND wiring  93  through the protection resistor R 2 . 
         [0061]    The above is the operation of the protection circuit  4  at time of the surge application. 
         [0062]    [Constraint on Capacity of Capacitors C 1  and C 2 ] 
         [0063]    In the above description, it is stated that the capacity of the capacitors C 1  and C 2  needs to be large enough. The constraint on this capacitance value will be described. 
         [0064]    With regard to the capacitance values of the capacitors C 1  and C 2 , when the maximum charge amount of a surae that is supposed to be applied to the electronic control device is Qs [C], and out of the withstand voltages of the internal circuit, and the input terminal for the sensor or the like, and the withstand voltages of the diode D 1  and D 2 , the lower one is Vmax, a capacity Cs of the capacitors needs to satisfy a inequality [Cs≧Qs/Vmax]. 
         [0065]    The inequality should apply due to the following reason. The capacitor C 1  or C 2  is charged by the surge application. If the charge voltages become large, the voltage of the input terminal  81  will also increase accordingly, and if either one of the withstand voltages of the internal circuit, and the input terminal  81  for the sensor or the like, and the withstand voltage of the reversely biased diode (D 2  at the time of application of a positive voltage surge or D 1  at the time of applying a negative voltage surge) is exceeded, they may be destroyed. 
         [0066]    To give a specific numerical value, the charge amount Qs of the surge is about 2.64 [nC], which is the product of the capacitance value (330 pF) of the storage capacitor Cs and the charge voltage (8 kV) under the application condition of static electricity as shown in  FIG. 7 . The withstand voltages of the internal circuit, and the input terminal for the sensor or the like, and the withstand voltage of the PN junction depend on a sensor and an internal circuit to be used, components used for the protection circuit, or a semiconductor process. Since a special process is needed for securing a withstand voltage larger than 100 V and the cost is high particularly in a semiconductor, Vmax is 100 [V] in this example. 
         [0067]    At this time, it can be understood that the capacitance value Cs of the capacitors C 1  and C 2  needs to be 0.264 [μF] or more from the following calculation formula. 
         [0000]        [Cs≧Qs/V max=2.64  [nC]/ 100[V]=0.0264 [μF]]
 
         [0068]    [Operation of Protection Circuit  4  at the Time of Battery Connection Abnormality] 
         [0069]    Next, the operation of the protection circuit  4  will be described when the battery  3  is reversely connected in polarity as battery connection abnormality. When the battery  3  is reversely connected in polarity, a Vb power supply serves as reversed polarity (negative voltage) relative to a GND potential, and unusual current tends to flow toward the Vb power supply wiring  92  from the OND wiring  93 . Thus, it is necessary to suppress it to a sufficiently small value. 
         [0070]    Here, unusual current in a path which passes through the power supply circuit  6  can be cut off within the power supply circuit  6 . With regard to a path from the GND wiring  93  to the input terminal  81  through the internal circuit  5 , since the internal circuit  5  has generally high impedance at its input, unusual current can be cut off here. 
         [0071]    The remaining paths lead to the input terminal  81  through the protection circuit  4  from the GND wiring  93 , and one of the remaining paths is a path  1  which passes through the capacitor C 2  and the diode D 2 , and the other is a path  2  which passes through the protection resistor R 2  and the diode D 2 . Here, with regard to the path  1 , since the capacitor C 2  does not pass direct current, unusual current can be cut off. With regard to the path  2 , unusual current can be suppressed to a low value by setting a resistance value Rp of the protection resistor R 2  to a sufficiently high value. 
         [0072]    From the above, it is possible to suppress unusual current due to battery connection abnormality in all possible paths to a sufficiently small value, and to protect the sensor or the like  2  and the protection circuit  4  itself. 
         [0073]    [Constraint on Resistance Value of Protection Resistor R 2 ] 
         [0074]    In the above description, it is stated that the resistance value Rp of the protection resistor R 2  needs to be large enough. The constraint on this resistance value will be described. 
         [0075]    A resistance value Rp of the protection resistor R 2  needs to satisfy the inequality, [Rp≧Vb×Vb/P], where battery voltage is Vb and an allowable dissipation of a package including the protection resistor R 2  is P. This is because when the resistance value Rp is small, unusual current flowing through the protection resistor R 2  increases and when the allowable dissipation P of the package is exceeded, the protection resistor R 2  is damaged due to burning or others, and thus the protection ability against a surge to be applied in another occasion may be lost. 
         [0076]    To give a specific numerical value, battery voltage Vb turns into a comparatively high voltage, when battery  3  is charged by an alternator, and the voltage Vb is generally around 14 [V] s. Although an allowable dissipation P of a package including the protection resistor R 2  depends on a package to be used, when the allowable dissipation P greatly exceeds 1 [W], generally special heat dissipation structure is needed, and the cost is high. Thus, the allowable dissipation P is set to 1 [W] in this example. 
         [0077]    At this time, it can be understood that a resistance value Rp of the protection resistor R 2  needs to be 196[Ω] or more from the following calculation formula. 
         [0000]        [Rp≧Vb×Vb/P= 14 [V]×14 [V]/1 [W]=196[Ω]]
 
         [0078]    [Other Constraint on Resistance Value of Protection Resistor R 2 ] 
         [0079]    Incidentally, the protection resistor R 2  has constraints with regard to a resistance value other than the above constraint. For example, there is an important constraint on a resistance value of the protection resistor R 2  is such that unusual current can be suppressed to a value smaller than the current value which is allowed to flow into the sensor or the like  2  from the input wiring  91 . However, this constraint largely depends on the specification of the sensor or the like  2  to be selected. Thus, it is difficult to define he value in general, and the values will not be calculated here. 
         [0080]    The above is an operation of the protection circuit  4  at the time of surge application and battery connection abnormality in the electronic control device  1  in this embodiment. 
         [0081]    [Mounting Method of Protection Circuit  4  on Integrated Circuit (Bulk Silicon)] 
         [0082]    Next, for the miniaturization of the electronic control device  1 , a mounting method for integrating a part of the protection circuit  4  into a bulk silicon chip will be described. The integration is made for elements shown inside of the broken line indicated by  41  in  FIG. 6 , i.e., the diodes D 1  and D 2 , and the protection resistors R 1  and R 2 . Hereinafter, the protection circuit in the dashed line of  41  is referred to as an integrated protection circuit  41 . Since C 1  and C 2  are not suitable for mounting on an integrated circuit as described in the “Problem to be Solved by the Invention”, they are not included as the object of integrated protection circuit  41  here. 
         [0083]    First, a section structure of the integrated protection circuit  41  in this mounting method will be described with reference to  FIG. 8 .  FIG. 8  is a view showing the section structure of the integrated protection circuit  41  in this mounting method. 
         [0084]    The integrated protection circuit  41  is roughly divided into a device layer  42  on which a semiconductor device is formed, and a wiring layer  43 , and the diodes D 1  and D 2  are formed in the device layer  42 , and the protection resistors R 1  and R 2 , and the wiring which connects elements inside and outside of the integrated protection circuit  41  are formed in the wiring layer  43 . 
         [0085]    The structure of the device layer  42  will be described in detail. First, the entire device layer  42  includes a p-sub (p-type substrate) region  421  of a p-type semiconductor as a base. An n type region  422  is formed in the p-sub region  421 , a p type region  423  is further formed in the n type region  422 , and the diode D 1  is constituted by a PN junction at the interface of the n type region  422 , and the p type region  423 . An n type region  424  is formed in another part, and a p type region  425  is further formed in the region  424 , and an n type region  426  is formed in the region  425 , and a PN junction at the interface of the p type region  425  and the n type region  426  constitutes diode D 2 . 
         [0086]    In the wiring layer  43 , the protection resistors R 1  and R 2  are formed using in polysilicon wiring, and a terminal  431  for connecting with the outside of the integrated protection circuit  41  is formed. 
         [0087]    [Separation of GND Wiring and Protection Element by Separation Layer Using PN Junction] 
         [0088]    These elements are connected in the wiring layer  43  in the basically same manner as the circuit block diagram of  FIG. 6 , and there are two additional connections. The first additional connection is that the p-sub region  421  is connected to the GND wiring  93  at the wiring layer. This is because if the p-sub region  421  is connected with no potential, this may have a bad influence through a stray capacitance or a parasite diode between the surrounding element or wiring, and it is necessary to fix the potential. 
         [0089]    The second additional connection is that the n type region  424  is connected to a wiring  95 . Accordingly, the n type region  424  is biased to an internal power supply potential Vcc through the protection resistor R 1 . Both PN junction  4251  between the n type region  424  and the p-sub region  421 , and PN junction  4252  between the n type region  424  and the p type region  425  are reversely biased, and this configuration thus functions as a separation layer which separates the p-sub region  421  and the diode D 2 . 
         [0090]    In cases where this separation layer does not exist, the p type region  425  which is an anode of the diode D 2  is electrically connected with the GND wiring  93  through the p-sub region  421 , and thus, unusual current cannot be suppressed by the protection resistor R 2  at the time of battery connection abnormality. With this separation layer, the insulation between the diode D 2  and the GNB wiring  93  can be secured, and the protection resistor R 2  can serve effectively. 
         [0091]    The above is a mounting method for integrating the integrated protection circuit  41  onto a bulk silicon chip. 
         [0092]    [Another Mounting Method of Protection Circuit  4  on Integrated Circuit (SOI)] 
         [0093]    Next, as an alternative method of integration of the integrated protection circuit  41 , a mounting method for integration on a chip of SOI (silicon on insulator) will be described. 
         [0094]    First, a section structure of the integrated protection circuit  41  in this mounting method will be described with reference to  FIG. 9 .  FIG. 9  is a view showing the section structure of the integrated protection circuit  41  in this mounting method. 
         [0095]    The integrated protection circuit  41  is roughly divided into a substrate layer  44 , a BOX layer  45 , a SOI layer  46 , and a wiring layer  43 . Diodes D 1  and D 2  are formed in the SOI layer  46 , and the wiring which connects the protection resistors R 1  and R 2  and elements inside and outside of the integrated protection circuit  41  are formed in the wiring layer  43 . 
         [0096]    While the substrate layer  44  is made of silicon and serves as a base for upper layers, neither a circuit element nor wiring is formed in this circuit. The BOX layer  45  is also called as an oxide film layer, and made of silicon oxide film. This layer has the role of electrically insulating the substrate layer  42  and the SOI layer  46 , which is disposed above the substrate layer  42 , and the presence of this BOX layer  45  is a feature of the SOI chip. The SOI layer  46  is made of silicon, corresponds to the device layer  42  at the time of mounting with bulk silicon, and is a layer on which a semiconductor device is formed. The wiring layer  43  has the same configuration as the wiring layer  43  at the time of mounting with the bulk silicon. 
         [0097]    The structure of the SOI layer  46  will be described in detail. First, the entire SOI layer  46  is based on a p type semiconductor region  461 . An n type region  462 , which is sandwiched by grooved oxide  469 , is formed on the region  461 , a p type region  463  is further formed in the region  462 , and a diode D 1  is constituted by a PN junction at the interface of the p type region  463  and the n type region  462 . Similarly in another part, a p type region  465 , which is sandwiched by grooved oxide  469 , is formed on the region  461 , a n type region  466  is further formed in the region  465 , and a diode D 2  is constituted by a PN junction at the interface between the p type region  465  and the n type region  466 . 
         [0098]    These elements are connected in basically the same manner as the circuit block diagram of  FIG. 6  within the wiring layer  43 . However, as an additional connection, the p type semiconductor region  461  and the substrate layer  42  are connected to the GND wiring  93  for fixation of potential. 
         [0099]    [Separation of GND Wiring and Protection Element by BOX Layer  45  and Grooved Oxide  469 ] 
         [0100]    In this mounting method, the insulation between the diode D 2  and the GND wiring  93  is achieved by the BOX layer  45  and the grooved oxide  469 . Compared with the insulation method with the reversely biased PN junction at the time of mounting with bulk silicon, this mounting method can ensure higher insulation performance such as smaller parasitic capacitance and less possibility of adverse effect by the parasitic element. 
         [0101]    The above is the mounting method for integrating the integrated protection circuit  41  onto a SOI chip. 
       Second Embodiment 
       [0102]    Next, the electronic control device according to the second embodiment of the present invention is described from the aspect of difference from the configuration in the first embodiment.  FIG. 10  is a circuit block diagram showing a configuration of an electronic control device  1  according to this embodiment. 
         [0103]    Although an electronic control device  1  in this embodiment has basically the same configuration as the electronic control device  1  in the first embodiment, an additional circuit is formed in a protection circuit  4 , in particular in an integrated protection circuit  41 . That is, a protection resistor R 3  and diodes D 3  and  04  are formed backward of diodes the D 1  and D 2  and the protection resistors R 1  and R 2 . 
         [0104]    [Operation of Protection Circuit  4  at the Time of Normal Operation] 
         [0105]    First, operation of protection circuit  4  at the time of normal operation will be described. The operation in the normal operation in the present embodiment is basically the same as that in the first embodiment. That is, the protection circuit  4  does not perform positive operation, but passes a signal from the input terminal  81 , and transmits it to the internal circuit  5 . Specifically, since a potential Vin of the input wiring  91  is between a GND potential and a potential Vcc of the internal power supply, the diodes D 3  and D 4  in addition to the diodes D 1  and D 2  are reversely biased, current does not flow during normal operation and an input signal is not interfered. 
         [0106]    [Operation of Protection Circuit  4  when Surge is Applied] 
         [0107]    Even when a surae is applied, components common to those in the first embodiment, i.e., the diodes D 1  and D 2 , the protection resistors R 1  and R 2 , and the capacitors C 1  and C 2  perform the same operation as those in the first embodiment. Difference is that the protection resistor R 3 , and the diodes D 3  and D 4 , which are added, perform an additional protection function. 
         [0108]    That is, as described in the first embodiment, the potential Vin of the input wiring  91  when the surge is applied can be suppressed to several tens of volts or less by the diode D 1  or D 2 , but according to an operation described below in this embodiment, a potential of an input wiring  97  of the internal circuit  5  can be suppressed to a further lower voltage. 
         [0109]    That is, when a surge of a positive voltage is applied, the diode D 3  is biased in the forward direction, and surge current flows into an internal power supply wiring  94  through the protection resistor R 3 . At this time, voltage can drop in the protection resistor R 3 , and the potential of the input wiring  97  can be lowered as compared with the potential of the input wiring  91 . 
         [0110]    When a surge of a negative voltage is applied, the diode D 4  is biased in the forward direction, and surge current flows from the GND wiring  93  through the protection resistor R 3 . At this time, voltage can drop in the protection resistor R 3 , and a potential of the input wiring  97  can be raised (the difference from the GND potential can be reduced) as compared with the potential of the input wiring  91 . 
         [0111]    The above is an operation of the protection circuit  4  in this embodiment, and the internal circuit  5  can be more effectively protected by this operation. 
         [0112]    Although the protection circuit  4  in the first and second embodiments describes the case where the number of the input terminals  81  is one for simplicity of description, the case where the number of the input terminals is two or more can also apply. In this case, the capacitors C 1  and C 2  and the protection resistors R 1  and R 2  may be shared for each input terminal. 
         [0113]    Various kinds of modifications as described above may be applied independently, or in any combination. 
       REFERENCE SIGNS LIST 
       [0114]      1 : electronic control device,  2 : sensor(s) or the like,  3 : battery,  4 : protection circuit,  5 : internal circuit,  6 : power supply circuit,  7 : surge source  41 : intearated protection circuit,  42 : device layer,  43 : wiring layer,  44 : substrate layer,  45 : box layer,  46 : SOI layer D 1 , D 2 , D 3 , D 4 : diode, R 1 , R 2 , R 3 : protection resistor, C 1 , C 2 : capacitor  81 : input terminal,  91 : input wiring,  92 : Vb power supply wiring,  93 : GND wiring,  94 : internal power supply wiring