Abstract:
A semiconductor device includes a current supply section configured to control a current flowing through a load circuit; an overcurrent detecting section configured to detect based on the current, that an overcurrent flows through the load circuit, to output an overcurrent signal; and an overheat detecting circuit configured to detect that a peripheral temperature exceeds a detected temperature, in response to the overcurrent signal, and output an overheat detection signal. The overheat detecting circuit has a hysteresis to the detection temperature, and the detection temperature contains an overheat detection temperature used to detect an overheat state and a recovery temperature used to detect to have escaped from the overheat state. The semiconductor device further includes a drive control circuit configured to output the current control signal which indicates the quantity of the current flowing through the load circuit based on the overcurrent signal and the overheat detection signal in the electric current supply section.

Description:
INCORPORATION BY REFERENCE 
     This patent application claims a priority on convention based on Japanese Patent Application No. 2009-209105 filed on Sep. 9, 2009. The disclosure thereof is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a semiconductor device, and especially relates to a semiconductor device and a circuit protecting method for detecting an overheat state to protect a circuit. 
     BACKGROUND ART 
     Conventionally, a relay is often used to control a large current and a high voltage. However, in an engine control unit (ECU) for automobile electric components, an IPD (Intelligent Power Device) has been increasingly used instead of the relay in these years. The IPD is provided with a circuit having a protection function around a power MOS transistor, and has a built-in self-diagnosis function. The IPD is able to transmit a self-diagnosis result to a control microprocessor. 
     For example, as disclosed in Patent Literature 1 (JP 2000-299631A), a power supply control apparatus is known which corrects a detection result of a current detecting circuit on the basis of a detection result of a temperature detecting circuit. The power supply control apparatus includes a semiconductor switch, a temperature detecting circuit, a current detecting circuit, and a control circuit. The semiconductor switch is switched in accordance with a control signal supplied to a control signal input terminal, and controls a power supply from a power supply to a load. The temperature detecting circuit detects a temperature of the semiconductor switch. The current detecting circuit detects a current flowing through the semiconductor switch on the basis of a voltage generated due to an on resistance of the semiconductor switch. The control circuit corrects a detection result by the current detecting circuit on the basis of the detection result of the temperature detecting circuit, and controls the supply of the control signal on the basis of the corrected detection current. 
     In addition, in Patent Literature 2 (JP 2001-257573A), a technique related to an electric load driving IC used as a driving circuit in en electric control apparatus is disclosed. When an abnormal state is detected by an abnormal state detecting circuit, a power disconnection signal for forcibly fixing a control signal to a logic level on a disconnection side is generated continuously, and the signal is outputted from a signal output terminal to outside of the electric load driving IC. 
     In Patent Literature 3 (JP 2003-297929A), a circuit device having a plurality of overheat detecting circuits is disclosed. In a driver IC of the circuit device, the plurality of overheat detecting circuits are arranged in adjacent to each other. Each of the overheat detecting circuits includes a temperature detecting section, a reference voltage generating circuit, a comparator, and a switch circuit. The reference voltage generating circuit generates a reference voltage by using the resistance division of the plurality of resistances. The comparator compares an output voltage of the temperature detecting section with the reference voltage. The switch circuit is connected to at least one of the plurality of resistances in parallel, and is turned on and off on the basis of the control signal. When the temperature is rapidly increased by a short-circuited load, the switch circuit is turned off on the basis of the control signal from an overcurrent detecting circuit. When the switch circuit is turned off, the reference voltage rises to lower an overheat detection temperature. In this manner, the circuit device changes the reference voltage generated through resistance division of the plurality of resistances on the basis of the control signal of the overcurrent detecting circuit to lower the overheat detection temperature, and thereby prevents malfunction due to the heat transfer from an detection target of the overheat detecting circuit. 
     In addition, Patent Literature 4 (JP-A-Heisei 11-34765) discloses a circuit protection device for vehicle that two types of threshold values are set for overheat detection. The circuit protection device includes an output, circuit, a control circuit, an instructing circuit, and a setting circuit. The output circuit supplies electric power to drive a load driving device provided in a vehicle. The control circuit controls an amount of the power to be supplied from the output circuit. The instructing circuit detects a temperature, and outputs a change signal to change the power supply amount controlled by the control circuit when the detection temperature exceeds a predetermined threshold value. The setting circuit replaces the threshold value with a new threshold value of a different value when the amount of power supply exceeds a predetermined value. In this manner, the circuit protection device for vehicle sets two types of threshold values of the overheat detection. 
     The above-mentioned circuit detects an abnormal overheated state caused by a rapidly-increasing overcurrent and, prevents device destruction caused by the current surge. Accordingly, the threshold value in an overcurrent state is set to a value between a normal threshold value in a detection temperature (for example, 175° C.) and a normal threshold value in a recovery temperature (for example, 150° C.). Therefore, in a case of being in the overcurrent state for a long time due to a short-circuit of a load, the circuit is maintained in a high temperature state of the normal recovery temperature (for example, 150° C.) or more or of a rated operation temperature range (for example, 150° C.) or more, and accordingly a long-term reliability cannot be assured for a resin and a bonding wire. 
     It is said that an Au—Al bonding deterioration is an important defect mode in a power device and this is because a cower device operates under severe surrounding environment and large power in a common specification and becomes a high temperature. In an automobile field, an assurance requirement of the junction temperature of up to 170° C. is general for a elastic package. In this case, the solution of the Au—Al bonding deterioration problem becomes a key to assure the reliability. 
     CITATION LIST 
     
         
         [Patent Literature 1]: JP 2000-299631A 
         [Patent Literature 2]: JP 2001-257573A 
         [Patent Literature 3]: JP 2003-297929A 
         [Patent Literature 4]: JP-A-Heisei 11-34765 
       
    
     SUMMARY OF THE INVENTION 
     In an aspect of the present invention, semiconductor device includes a current supply section configured to control a current flowing through a load circuit; an overcurrent detecting circuit configured to detect based on the current, that an overcurrent flows through the load circuit, to output an overcurrent signal; and an overheat detecting circuit configured to detect that a peripheral temperature exceeds a detected temperature, in response to the overcurrent signal, and output an overheat detection signal. The overheat detecting circuit has a hysteresis to the detection temperature, and the detection temperature contains an overheat detection temperature used to detect an overheat state and a recovery temperature used to detect to have escaped from the overheat state. The semiconductor device further includes a drive control circuit configured to output the current control signal which indicates the quantity of the current flowing through the load circuit based on the overcurrent signal and the overheat detection signal in the electric current supply section. 
     In another aspect of the present invention, a circuit protection method is achieved by detecting an overcurrent flowing through a load circuit; by detecting an overheat state in which a peripheral temperature exceeds a detection target temperature; by changing the detection target temperature from a first detection temperature to a second detection temperature which is lower than the first detection temperature, for a predetermined time period after the detection of the overcurrent; and controlling a quantity of the current flowing through the load circuit based on the detection of the overheating state and the detection of the overcurrent. When it is detected that the peripheral temperature exceeds the detection target temperature, the first detection temperature is set to a first recovery temperature and the second detection temperature is set to a second recovery temperature. When it is detected that the peripheral temperature falls lower than the detection target temperature, the first detection temperature is set to a first overheat temperature which is higher than the first recovery temperature and the second detection temperature is set to a second overheat temperature which is higher than the second recovery temperature. 
     According to the present invention, a semiconductor device and a circuit protection method for preventing a continuation of an abnormal high temperature state and realizing an assurance of a long-term reliability can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram showing a configuration of an ECU as a semiconductor device according to a first embodiment of the present invention; 
         FIG. 2  is a diagram showing a configuration example of an overcurrent detecting circuit of the present invention; 
         FIG. 3  is a diagram showing a configuration of an overheat detecting circuit of the present invention; 
         FIG. 4  is a diagram showing an overheat detection operation of the ECU according to the first embodiment of the present invention; 
         FIG. 5  is a diagram showing a configuration of an ECU according to a second embodiment of the present invention; 
         FIG. 6  is a diagram explaining an overheat detection operation of the ECU according to the second embodiment of the present invention; 
         FIG. 7  is a diagram explaining another overheat detection operation of the present invention; and 
         FIG. 8  is a diagram showing a configuration example of another overheat detecting circuit of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a block diagram of a semiconductor device according to a first embodiment of the present invention. As the semiconductor device, an engine control unit (ECU) for an automobile electric component is exemplified. An engine control unit  10  includes a control circuit  12  having a memory  35 , and a load driving circuit  11 , and controls an electric current flowing through a load circuit  15 . 
     The load driving circuit  11  includes an output transistor  21 , an overcurrent detecting circuit  23 , a detection period setting circuit  24 , an overheat detecting circuit  27 , a drive control circuit  31 , and an abnormal state notifying circuit  33 . The output transistor  21  controls a current flowing through the load circuit  15  in response to a control signal s outputted from the drive control circuit  31 . A drain voltage Vd of the output transistor  21  is supplied to the overcurrent detecting circuit  23 . 
     As shown in  FIG. 2 , the overcurrent detecting circuit  23  includes a comparator  50  and resistance elements  61  and  62 . The comparator  50  compares a reference voltage VREF 1  with the drain voltage Vd of the output transistor  21 , and outputs an overcurrent detection signal a (corresponding to a signal a 1  of the load driving circuit  11 ). The reference voltage VREF 1  is generated by dividing a stable power supply voltage VCC by the resistance elements  61  and  62 . When resistance values of the resistance elements  61  and  62  are R 1  and R 2 , the reference voltage VREF 1  is
 
 V REF1 =VCC×R 2/( R 1+ R 2).
 
     During a normal operation in the load circuit  15 , the drive control circuit  31  applies a bias to the output transistor  21  so that the drain voltage Vd cannot influence the operation of the load circuit  15 . When an abnormal current flows due to a short-circuit in the load circuit  15 , the drain voltage Vd rapidly rises. When the drain voltage Vd rises to be higher than the reference voltage VREF 1 , the comparator  50  sets the overcurrent detection signal a active (a high level). 
     When a current supplied to the load circuit  15  is blocked off, the drain voltage of the output transistor  21  becomes high, and thus, the overcurrent detecting circuit  23  sets the overcurrent detection signal a 1  active in the same manner as that of the detection of overcurrent. Accordingly, the detection period setting circuit  24  processes the overcurrent detection signal a 1  so as to represent that a normal current has been supplied to the load circuit  15  and that the overcurrent has been detected in a period during which the overcurrent has to be detected. Here, the detection period setting circuit  24  includes an AND Circuit. While a reset signal r 1  outputted from the drive control circuit  31  is in a high level, the detection period setting circuit  24  outputs a signal outputted from the drive control circuit  31  as an overcurrent signal b 1 . Accordingly, when the output transistor  21  blocks the current supplied to the load circuit  15 , a detection error of overcurrent can be prevented by setting the reset signal to a low level. In addition, when an overcurrent flows through the load circuit  15  and the current is blocked, a detected state of the overcurrent can be maintained by setting the reset signal r 1  to the high level. The detection of the overcurrent is notified to the drive control circuit  31  and the abnormal state notifying circuit  33  by the overcurrent signal b 1 . 
     As shown in  FIG. 3 , the overheat detecting circuit  27  includes a comparator  51 , resistance elements  63  to  65 , switch circuits  57  and  58 , diodes  52  and  53 , and a constant current source  55 . The diodes  52  of the predetermined number are connected in series. In an example shown in  FIG. 3 , three diodes are connected in series. The constant current source  55  and the diodes  52  and  53  are connected in series, and a voltage Va at a connection node between the constant current source  55  and the diodes  52  is given to one of inputs of the comparator  51 . A forward voltage when a constant current is supplied to the diodes  52  and  53  varies depending on a junction temperature. When the junction temperature is increased, the forward voltage is lowered, and when the junction temperature is reduced, the forward voltage rises. That is, the diodes  52  and  53  serve as temperature sensors, and the voltage Va varies depending on the junction temperature. The overheat detecting circuit  27  detects an overheat state by using a temperature characteristic of the forward voltage Va of the diodes  52  and  53 . 
     The switch circuit  57  is connected to the diode  53  in parallel and is controlled by an overcurrent signal b (equivalent to an overcurrent signal b 1  outputted from the detection period setting circuit  24  in the present embodiment). When the overcurrent signal b is inactive (low level) and the switch circuit  57  is in an open state, the forward current flows through the diodes  52  and  53 , a summation of the forward voltages (the voltages of the four diodes in  FIG. 3 ) becomes the voltage Va. When the overcurrent signal b becomes active (high level) and the switch circuit  57  is in a close state, the diode  53  is bypassed by the switch circuit  57 . Thus, the voltage Va represents the forward voltages of the diodes  52 . That is, the voltage Va is controlled by the overcurrent signal b, and an overheat detection temperature can be changed depending on the overcurrent signal b. 
     The voltage Va of the temperature sensor is obtained as follows. It is assumed that a forward voltage of a diode when a peripheral temperature Ta is equal to 25° C. is VF and the number of temperature sensor diodes is N. In this case, the voltage Va when the peripheral temperature is 25° C. is:
 
 Va=VF×N  
 
Since the forward voltage of the diode has a negative correlation to the temperature, it is assumed that a temperature coefficient thereof is θ. In this case, the voltage Va of the temperature sensor in the peripheral temperature Ta is
 
 Va =( VF −θ×( Ta− 25))× N  
 
For example, as shown in  FIG. 3 , it is assumed that the number N of diodes for the temperature sensor is four and that the comparator  51  is configured so as to detect the overheat state of 175° C. Since the voltage Va for the temperature sensor to be compared are same, the temperature Ta at which the overheat state is detected when the number N of diodes is switched to three is obtained from:
 
( VF −θ×(175−25))×4=( VF −θ×( Ta− 25))×3
 
When the diode forward voltage VF in the peripheral temperature of 25° C. is 0.7V and the temperature coefficient θ is equal to 0.002 V/° C., it is obtained that Ta is nearly equal to 108° C. That is, the overheat detection temperature when the number of diodes for the temperature sensor is switched to be three is reduced to 108° C.
 
     The voltage Va of this temperature sensor is compared with a reference voltage VREF 2  generated by the resistance elements  63  to  65 . The overheat detection temperature is set by adequately setting the resistance elements  63  to  55 . The resistance elements  63  to  65  are connected in series and the reference voltage VREF 2  is generated by dividing the stable power supply voltage VCC by the resistance elements. A desired overheat detection temperature can be obtained by adequately setting: the forward voltages of the diodes  52  and  53 , and the reference voltage VREF 2 . 
     In addition, the switch circuit  58  is connected to the resistance element  63  in parallel and controlled by an output of the comparator  51 . Accordingly, the reference voltage VREF 2  varies depending on the output of the comparator  51 . 
     When the normal operation is carried out and the junction temperature is low, the voltage Va is higher than the reference voltage VREF 2 , and an overheat detection signal c that is the output of the comparator  51  is inactive (low level). In this case, the switch circuit  58  is in an open state. When the resistance values of the resistance elements  63  to  65  are R 3  to R 5 , respectively, the reference voltage VREF 2  (or a voltage VREF 21 ) is:
 
 V REF21 =VCC×R 5/( R 3+ R 4+ R 5)
 
     When the junction temperature is high, the voltage Va becomes lower than the reference voltage VREF 2 . Accordingly, the overheat detection signal c becomes active (high level), and the switch circuit  58  is turned into a close state. The switch circuit  58  bypasses the resistance element  63 , and at this time, the reference voltage VREF 2  (or a voltage VREF 22 ) is
 
 V REF22 =VCC×R 5/( R 4+ R 5)
 
Since the reference voltage VREF 21  is less than the reference voltage VREF 22 , the overheat detection signal c does not become inactive (low level) if the overheat detection signal c does not become a higher voltage than that at which the overheat detection signal c becomes active (high level), that is, the junction temperature does not become lower. Due to the switch circuit  58 , the overheat detecting circuit  27  has hysteresis as a result. A width of the hysteresis can be adjusted by the resistance elements  63  to  65 . For example, resistance values R 3  to R 5  of the resistance elements  63  to  65  can be set so that the overheat detection temperature can be 175° C. and the recovery temperature can be 150° C. In this case, when the number of diodes for the temperature sensor is switched from four to three to lower the overheat detection temperature to 108° C., the recovery temperature is also lowered to 83° C.
 
     The overheat detection signal c generated in this manner is outputted to the drive control circuit  31  and the abnormal state notifying circuit  33 . In response to a control instruction signal t outputted from the control circuit  12 , the drive control circuit  31  controls the output transistor  21  to supply a current to the load circuit  15  and to stop the supply. During the supply of current to the load circuit  15 , the drive control circuit  31  restricts the current supplied to the load circuit  15  in response to the overcurrent signal b 1 , and blocks off the current supplied to the load circuit  15  in response to the overheat detection signal c. It can be prevented to unnecessarily apply a large current and to be high temperature by restricting and blocking off the supply current. 
     In addition, the drive control circuit  31  outputs a reset signal r 1  to the detection period setting circuit  24  to set a detection period of the overcurrent. This reset signal r 1  will be in a high level at a time of start of the current supply shown by the control instruction signal t outputted from the control circuit  12 , and validates the detection of overcurrent. The reset signal r 1  will be in a low level while the control instruction signal t instructs the stop of the current supply, and invalidates the detection of overcurrent. 
     In response to the overcurrent signal b 1 , the abnormal state notifying circuit  33  recognizes occurrence of an abnormal state that the overcurrent has flowed through the load circuit  15 . In addition, the abnormal state notifying circuit  33  recognizes in response to the overhear detection signal c, that the abnormal state that the temperature around the overheat detecting circuit  27  has become high has occurred. Upon the detection of these abnormal states, the abnormal state notifying circuit  33  outputs an abnormal state warning signal e to notify the occurrence of the abnormal state to the control circuit  12 . 
     The control circuit  12  stores data representing the notified abnormal state in the memory  35 , and outputs a diag code d including data of these abnormal states from a DIAG terminal  37  in response to a request from the outside. In addition, in response to an instruction signal u from the outside, the control circuit  12  outputs the control instruction signal t to the drive control circuit  31  to instruct the drive control circuit  31  to start and stop the driving of the output transistor  21 . 
     Referring to  FIG. 4 , an operation of the engine control unit  10  will be described. The engine control unit  10  receives the instruction to drive the load circuit  15 . When receiving an instruction signal u instructing to start the current supply, the control circuit  12  sets the control instruction signal t to be active (high level) ((a) of  FIG. 4 ). The drive control circuit  31  sufficiently increases the current control signal s supplied to a gate of the output transistor  21 , and sets the output transistor  21  to be in an on state ((c) of  FIG. 4 ). In addition, the drive control circuit  31  sets the reset signal r 1  supplied to the detection period setting circuit  24  to be in a high level, and validate the overcurrent detection ((b) of  FIG. 4 ). An on-resistance of the output transistor  21  is set to be sufficiently small so as not to influence the operation of the load circuit  15 . That is, the gate voltage of the output transistor  21  at this time is set to be relatively high. 
     When the output transistor  21  is in the on state, a current flows through the load circuit  15  and also flows through the output transistor  21  connected in series as the drain current Id ((d) of  FIG. 4 ). In this case, the current the normal operation flows, and the drain voltage Vd becomes lower than a detection level ((e) of  FIG. 4 ). The overcurrent detecting circuit  23  does not detect the overcurrent, and accordingly sets the overcurrent detection signal a 1  to be inactive (low level) ((f) of  FIG. 4 ). The overcurrent signal b 1  outputted from the detection period setting circuit  24  is set to be inactive (low level) to indicate the normal operation state ( FIG. 4(   g )). Accordingly, the switch  57  of the overheat detecting circuit  27  is opened, and the overheat detecting circuit  27  compares a voltage Va representing a voltage drop of the diodes  52  and diode  53  connected in series with the reference voltage VREF 2  (the voltage VREF 21 ). 
     Here, when the load circuit  15  is short-circuited due to a certain cause, an abnormal current flows. When the drain voltage Vd of the output transistor  21  exceeds a predetermined detection level (a dashed line in (e) of  FIG. 4 ) due to the abnormal current, the overcurrent detecting circuit  23  sets the overcurrent detection signal a 1  to be active (high level) as shown in  FIG. 4(   f ). When the overcurrent detection signal a 1  becomes active, the reset signal r 1  is in a high level, and accordingly the detection period setting circuit  24  sets the overcurrent signal b 1  to be in the high level to notify the overcurrent ((g) of  FIG. 4) . When the detection of overcurrent is notified, the drive control circuit  31  lowers the current control signal s to restrict the current flowing through the load circuit  15  ((c) and (d) of  FIG. 4 ). Meanwhile, when the overcurrent signal b 1  becomes active, the overheat detecting circuit  27  closes the switch  57  to switch the detection temperature setting. In the present embodiment, the overheat detection temperature is switched from 175° C. to 108° C., and the recovery temperature is switched from 150° C. to 83° C., for example ((h) of  FIG. 4 ). 
     When the temperature rises and the junction temperature of the temperature sensor exceeds the overheat detection temperature (108° C. here) ((b) of  FIG. 4 ), the overheat detecting circuit  27  sets the overheat detection signal c to be active (high level) ((i) of  FIG. 4 ). When the overheat detection signal c becomes active, the drive control circuit  31  controls the current control signal s so as to block off the supply current ( FIG. 4(C) ). Accordingly, the current flowing through the output transistor  21  is blocked off ((d) of  FIG. 4 ). In this case, as shown in (e) of  FIG. 4 , the voltage Vd exceeds the detection level. Thus, as shown in (f) of  FIG. 4 , the output (the overcurrent detection signal a 1 ) of the overcurrent detecting circuit  23  is maintained in the active (high level) state. In addition, when the overheat detection signal c becomes active, the switch  58  bypasses the resistance element  63 . In this manner, if the peripheral temperature of the temperature sensor does not fall lower than the recovery temperature (83° C. here), the comparator  51  does not set the overheat detection signal c to be inactive (low level) ((h) and (i) of  FIG. 4 ). 
     When the supply current stops and the peripheral temperature of the temperature sensor has dropped due to stop of the heat generation of the load circuit  15 , the forward voltage of the diodes of temperature sensor rises. When the peripheral temperature becomes lower than the recovery temperature (83° C. in this example), the overheat detection signal c is cancelled and becomes inactive (low level) ((i) of  FIG. 4 ). That is, after the voltage Va sufficiently raised, the overheat detection signal c becomes inactive. The switch  58  is opened, the resistance element  64  is connected to the power supply voltage VCS: via the resistance element  63 , and thus the reference voltage VREF 2  drops. When the overheat detection signal c becomes inactive, the drive control circuit  31  raises the current control signal s connected to the gate of the output transistor  21  to restart the current supply to the load circuit  15  ((c) of  FIG. 4 ). In this case, if the cause by which the load circuit  15  is short-circuited is eliminated, the load circuit  15  is driven in a normal current value. However, as shown in  FIG. 4 , the overcurrent is detected and accordingly the supply current is restricted when the short-circuited state continues. When the heat-generation further continues, the overheat state is detected and the supply current is blocked. This operation is repeated while the instruction to drive the load circuit  15  continues. This repetition period for which the overheat detection is repeated is called a thermal toggle period. 
     When the control instruction signal t is set to be in the off state ((a) of  FIG. 4 ), the drive control circuit  31  stops the current supply to the load circuit  15 . In this case, the drive control circuit  31  sets the reset signal r 1  to be in the low level and outputs the signal to the detection period setting circuit  24 , and the overcurrent signal b 1  becomes inactive after the overcurrent detection ends ( FIG. 4(   g )). When the overcurrent signal b 1  becomes inactive, the overheat detecting circuit  27  opens the switch  57 , and resets the overheat detection temperature and the recovery temperature to be the preset temperatures (175° C. and 150° C. here) ((h) of  FIG. 4) . 
     The overcurrent signal b 1  and the overheat detection signal c are both supplied to the abnormal state notifying circuit  33 . The abnormal state notifying circuit  33  notifies to the control circuit  12  that the overcurrent has flowed and that the overheat state has detected, and the control circuit  12  stores the notice in the built-in memory  35 . When receiving the instruction signal u for data output, the control circuit  12  outputs the data of these abnormal states as a diag code d via the DIAG terminal  37 . 
     As described above, in a simple circuit configuration, it is able to lower the overheat detection temperature when detecting the overcurrent and thus to control current supply so that the overheat state is not continued for a long period. Accordingly, the operation can be carried out for the long period without exceeding a rated operation temperature range, and thus a long-term reliability can be assured. In addition, since data representing the abnormal state is stored and can be outputted arbitrarily, only the load device  15  in the abnormal state can be replaced. Moreover, when receiving the notice of the abnormal state occurrence, the control circuit  12  may notify the abnormal state occurrence to outside without an instruction from the outside. 
     Since the occurrence of an abnormal state is notified to the control circuit  12  and the supply current is blocked, the ECU itself can be protected and repairing is sufficient by replacing only the load device  15 . When the ECU recognizes the abnormal state occurrence, an engine check lamp is lit so as to warn a driver. In this case, a data indicative of a portion in the abnormal state is stored in the ECU and is not erased only by turning off a power supply. An operation to read the stored data is the read of the diag code. When an abnormal state code is read, a recovery operation can be carried out efficiently by checking and repairing the portion preferentially. 
       FIG. 5  shows a block diagram of a semiconductor device according to a second embodiment of the present invention. Compared to the first embodiment, in the second embodiment, the output transistor  21  is replaced by a multi-source output transistor  22 , and the detecting method of the overcurrent is changed. As the semiconductor device, the engine control unit (ECU) for an automobile electric component is exemplified. The engine control unit  10  includes the control circuit  12  having the memory  35 , and the load driving circuit  11 , and controls and drives a current flowing through the load circuit  15 . 
     The load driving circuit  11  includes the output transistor  22 , the overcurrent detecting circuit  23 , a latch circuit  25 , the overheat detecting circuit  27 , the drive control circuit  31 , and the abnormal state notifying circuit  33 . The output transistor  22  controls the current flowing through the load circuit  15  in response to the control signal s outputted from the drive control circuit  31 . The drain current Id of the output transistor  22  flows via a plurality of sources. Most of the sources is for the load current, and other sources are for supplying a current proportional to the load current to a resistance element  28  such that a voltage Vs generated in the resistance element  28  is outputted to the overcurrent detecting circuit  23 . 
     The overcurrent detecting circuit  23  is the same as the circuit shown in  FIG. 2  which has been described in the first embodiment, and accordingly the detailed description is omitted. The overcurrent detecting circuit  23  indirectly measures the drain current Id by using the voltage Vs generated by the resistance element  28 . During the normal operation of the load circuit  15 , the drive control circuit  31  applies a bias to a gate of the output transistor  22  so that the drain voltage Vd cannot influence the operation of the load circuit  15 . When an abnormal current flows due to a short-circuit defect of the load circuit  15 , the voltage Vs rapidly rises. When the voltage Vs rises to be higher than the reference voltage VREF 1 , the comparator  50  sets the overcurrent detection signal a (shown as the signal a 2  in  FIG. 5 ) to be active (the high level). 
     The overcurrent detecting circuit  23  notifies the detection of overcurrent to the drive control circuit  31  and the abnormal state notifying circuit  33  by the overcurrent detection signal a 2 . In addition, the overcurrent detection signal a 2  is also supplied to the latch circuit  25 . The latch circuit  25  includes a flip-flop (not shown) and holds the state of the overcurrent detection and outputs the overcurrent signal b 2  to the overheat detecting circuit  27 . The latch circuit  25  resets the overcurrent detection state in response to the reset signal r 2  outputted by the drive control circuit  31 . 
     The overheat detecting circuit  27  is the same as the circuit shown in  FIG. 3 , which has been described in the first embodiment, and accordingly the detailed description is omitted. However, the circuit has hysteresis and can change the overheat detection temperature in accordance with the overcurrent signal b 2 . The overheat detection signal c generated by the overheat detecting circuit  27  is supplied to the drive control circuit  31  and the abnormal state notifying circuit  33 . In response to the control instruction signal t outputted from the Control circuit  12 , the drive control circuit  31  controls the output transistor  22  to supply a current to the load circuit  15  and to stop the supply. During the supply of current to the load circuit  15 , the drive control circuit  31  restricts the current supplied to the load circuit  15  in response to the overcurrent detection signal a 2 , and blocks off the current supplied to the load circuit  15  in response to the overheat detection signal c. By restricting and blocking the supply current, it is possible to prevent the supply of unnecessarily-large current and rise to a high temperature. 
     In addition, the drive control circuit  31  outputs the reset signal r 2  to reset the latch circuit  25  for holding the overcurrent detection state. It is preferable that the reset signal r 2  is set active to reset the latch circuit  25 , when the control instruction signal t outputted from the control circuit  12  shows the start of current supply. The reset signal r 2  may be active during a period during which the control instruction signal t instructs the stop of current supply. 
     In response to the overcurrent detection signal a 2 , the abnormal state notifying circuit  33  recognizes occurrence of the abnormal state that the overcurrent flows through the load circuit  15 . Or, the abnormal state due to the overcurrent may be recognized by the overcurrent signal b 2 . In addition, the abnormal state notifying circuit  33  recognizes in response to the overheat detection signal c, that the abnormal state that the peripheral temperature of the overheat detecting circuit  27  becomes high has occurred. The abnormal state notifying circuit  33  outputs an abnormal state warning signal e to notify occurrence of these abnormal states to the control circuit  12 . 
     The control circuit  12  stores data indicating the notified abnormal states in the memory  35 , and outputs the diag code d including the data indicative of these abnormal states from the DIAG terminal  37  in response to a request from the outside. In addition, in response to the instruction signal u from the outside, the control circuit  12  outputs the control instruction signal t to instruct the drive control circuit  31  to start and stop the driving of the output transistor  22 . 
     Referring to  FIG. 6 , the operation of the engine control unit  10  will be explained. 
     The engine control unit  10  receives an instruction to drive the load circuit  15 . When receiving the instruction signal u instructing to start the current supply, the control circuit  12  sets the control instruction signal t to be active (high level) ((a) of  FIG. 6 ). The drive control circuit  31  sufficiently increases the current control signal s supplied to a gate of the output transistor  22  and sets the output transistor  22  to be in an on state ((c) of  FIG. 6 ). An on resistance of the output transistor  22  is set to be sufficiently small so as not to influence the operation of the load circuit  15 . That is, the gate voltage of the output transistor  22  at this time is set to be high. 
     When the output transistor  22  is in the on state, a current flows through the load circuit  15  and also flows through the output transistor  22  connected in series as the drain current Id ((d) of  FIG. 6 ). In this case, the current in the normal operation flows, the overcurrent detecting circuit  23  does not detect the overcurrent, and the overcurrent detection signal a 2  represents the inactive state (low level) ((f) of  FIG. 6 ). The latch circuit  25  shows the normal operation state and the overcurrent latch signal b 2  is set to be inactive (low level) ((g) of  FIG. 6 ). Accordingly, the switch  57  of the overheat detecting circuit  27  is opened, and the overheat detecting circuit  27  compares the voltage Va due to a voltage drop of the diodes  52  and diode  53  connected in series with the reference voltage VREF 2  (the voltage VREF 21 ). 
     Here, when the load circuit  15  is short-circuited due to a certain cause, an abnormal current flows and the drain voltage Vd of the output transistor  22  rises. When the voltage Vs of the resistance  28  exceeds a predetermined detection level (a dashed line in (d) of  FIG. 6 ) due to the abnormal current, the overcurrent detecting circuit  23  sets the overcurrent detection signal a 2  to be active (high level) as shown in (f) of  FIG. 6 . When the overcurrent detection signal a 2  is set to be active, the drive control circuit  31  decreases the level of the current control signal s to restrict the current flowing through the load circuit  15  ((c) and (d) of  FIG. 6 ). Meanwhile, the latch circuit  25  latches the overcurrent detection signal a 2  and raises the overcurrent signal b 2  (high level) as shown in (g) of  FIG. 6 . When the overcurrent latch signal b 2  is set to be active, the overheat detecting circuit  27  closes the switch  57  to switch the detection temperature setting. In the present embodiment, the overheat detection temperature is switched from 175° C. to 108° C., and the recovery temperature is switched from 150° C. to 83° C., for example ((h) of  FIG. 6 ). 
     When the temperature rises and the junction temperature of the temperature sensor exceeds the overheat detection temperature (108° C. here) ((h) of  FIG. 6 ), the overheat detecting circuit  27  sets the overheat detection signal c to be active (high level) ((i) of  FIG. 6 ). When the overheat detection signal c is set to be active, the drive control circuit  31  controls the current control signal s so as to block off the supply current ((c) of  FIG. 6 ). Accordingly, the current flowing through the output transistor  22  is blocked off ((d) of  FIG. 6 ). In addition, when the overheat detection signal c is set to be active ((i) of  FIG. 6 ), the switch  58  bypasses the resistance element  63 . In this manner, if the peripheral temperature of the temperature sensor does not falls lower than the recovery temperature (83° C. here), the comparator  51  does not set the overheat detection signal c to be inactive (low level). 
     When the current supply is stopped so that the peripheral temperature of the temperature sensor decreases, the forward voltage of the diodes as the temperature sensor rises. When the peripheral temperature becomes lower than the recovery temperature (83° C. here), the overheat detection signal c is set to be inactive (low level) ((h) and (i) of  FIG. 6 ). That is, after the voltage Va sufficiently raises, the overheat detection signal c is set to be inactive. The switch  58  is opened, the resistance element  64  is connected to the power supply voltage VCC via the resistance element  63 , and thus the reference voltage VREF 2  falls. When the overheat detection signal c is set to be inactive, the drive control circuit  31  raises the current control signal s ((c) of  FIG. 6 ) to restart the current supply to the load circuit  15  ((d) of  FIG. 6 ). In this case, if the cause of a state that the load circuit  15  is short-circuited is removed, the load circuit  15  is driven in a normal current value. However, as shown in  FIG. 6 , the overcurrent is detected while the short-circuited state continues, the current supply is restricted. Or, the current supply is maintained to be restricted while the overcurrent signal b 2  is in the active state (high level). 
     When the control instruction signal t is turned off ((a) of  FIG. 6 ), the drive control circuit  31  stops the current supply to the load circuit  15 . In this case, the drive control circuit  31  outputs the reset signal r 2  to the latch circuit  25  to reset the signal ((b) of  FIG. 6 ). Or, the latch circuit  25  is reset when the control instruction signal t instructs next start of the current supply. In the case of the resetting in response to the instruction of the start of the current supply, when the control instruction signal t is set to be active (high level), the drive control circuit  31  raises the current control signal s, and outputs the reset signal r to the latch circuit  25  to reset the overcurrent latch signal b. When the overcurrent signal b 2  is reset ((g) of  FIG. 6 ), the overheat detection temperature and the recovery temperature are reset to the normal preset temperatures (175° C. and 150° C. here) ((h) of  FIG. 6 ). 
     The overcurrent signal a and the overheat detection signal c are also supplied to the abnormal state notifying circuit  33 . The abnormal state notifying circuit  33  notifies to the control circuit  12  that the overcurrent flows and that the overheat state is detected, and the control circuit  12  stores the notices in the built-in memory  35 . When receiving the instruction signal u instructing to output data, the control circuit  12  outputs the data of these abnormal states as a diag code via the DIAG terminal  37 . 
     As described above, in the simple circuit configuration, it is able to lower the overheat detection temperature when detecting the overcurrent and to control the current supply so that the overheat state is not continued for a long period. Accordingly, the operation can be carried out for the long period without exceeding a rated operation temperature range, and thus a long-term reliability can be assured. In addition, since the data of the abnormal states are stored and can be outputted arbitrarily, the repairing can be performed only by replacing the load device  15 . Moreover, when receiving the notice of the abnormal state occurrence, the control circuit  12  may notify the abnormal state occurrence to an outside without any instruction from the outside. 
     Since the abnormal state occurrence is notified to the control circuit  12  and the supply current is blocked, the ECU itself can be protected and the abnormal state can be eliminated by replacing only the load device  15 . When the ECU recognizes the abnormal state occurrence, an engine check lamp is lit so as to warn a driver. In this case, data indicating the cause portion of the abnormal state is stored in the ECU and is not erased only by turning off the power supply. An operation to read the stored data is the read of the diag code. When a trouble code is read, a recovery operation can be carried out efficiently by checking and repairing the portion preferentially. 
     In the above description, the latch circuit  25  is exemplified as a circuit that is set in response to the overcurrent detection signal a 2  outputted from the overcurrent detecting circuit  23  and is reset in response to the reset signal r 2  outputted from the drive control circuit  31 . The circuit for holding the overcurrent signal b 2  is not limited to this example, and may be a circuit such as a retriggerable one-shot multivibrator for outputting a pulse having a longer time width than the thermal toggle period when the overcurrent detection signal a is given as a trigger. In this case, as shown in (g) of  FIG. 7 , the overcurrent latch signal b 2  is set to be active (high level) when there is a next rising edge in a period for which a predetermined time p has passed from the rising edge of the overcurrent detection signal a 2 , and is set to be inactive (low level) in when there is not the rising edge in the period for which the predetermined time has passed. In this case, it is required to adequately set the predetermined time. The operations of the other circuits are the same as those of the first embodiment, and accordingly the descriptions are omitted. 
     In addition, as shown in  FIG. 3 , the overheat detecting circuit  27  is exemplified as the circuit for determining the overheat state by the comparator  51  by using the forward voltage of the diodes as the temperature sensor. However, as shown in  FIG. 8 , the inverter circuit can be used. 
     In this case, the overheat detecting circuit  27  includes Schmitt trigger-type inverters  71  and  72 , a constant current source  74 , a diode  75 , and a switch  76 . The forward voltage Va of the diode  75  varies clue to the constant current outputted from the constant current circuit  74  in accordance with a peripheral temperature. A voltage level of the forward voltage Va is determined by the inverters  71  and  72 . The inverter  71  has hysteresis in which a rising threshold value is set to a normal overheat detection temperature (for example, 175° C.) and a falling threshold value is set to a normal recovery temperature (for example, 150° C.). The inverter  72  has hysteresis in which a rising threshold value is set to the overheat detection temperature in the overcurrent detection (for example, 108° C.) and a falling threshold value is set to the recovery temperature in the overcurrent detection (for example, 83° C.). One of the output of the inverter  71  and the output of the inverter  72  is selected by the switch  76 , and is outputted as the overheat detection signal c. The switch  76  selects the output of the inverter  71  or the output of the inverter  72  in response to the overcurrent signal b. 
     Accordingly, in the same manner as that of the above-mentioned overheat detecting circuit  27 , the overheat detecting circuit  27  having the inverter circuit can operate to switch the overheat detection temperature and the recovery temperature in the overheat detection operation having the hysteresis depending on the detection of overcurrent. 
     In the above-mentioned description, as a method for switching the detection temperature, a method of switching the number of diodes of the temperature sensor, and a method of switching of the reference voltage has been exemplified. However, the method may switch the bias current applied to the diodes of the temperature sensor. 
     As described above, according to the present invention, in the simple circuit configuration, it is able to lower the overheat detection temperature when detecting the overcurrent and to control the current supply so that the overheat state is not continued for a long period. Accordingly, a long-term reliability of a resin and a bonding wire can be attained from the overheat state. In addition, since data representing an abnormal state is stored and can be outputted arbitrarily, the abnormal state can be eliminated by replacing only the load device causing the abnormal state. 
     Although the present invention has been described above in connection with several embodiments thereof, it would be apparent to those skilled in the art that those embodiments are provided solely for illustrating the present invention, and should not be relied upon to construe the appended claims in a limiting sense.