JP2006261143A - Thermal protection circuit and semiconductor integrated circuit device provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal protection circuit capable of executing highly accurate thermal protection operation without depending on superposition of noises etc., and a semiconductor integrated circuit device provided with the same. <P>SOLUTION: In the thermal protection circuit 10, a first comparator 123 is driven based on an output signal of a second comparator 124, only when a temperature to be monitored is larger than a second threshold temperature defined by a second threshold voltage Vth2; a first DC voltage source 121 generates a first threshold voltage Vth1 of a voltage level equivalent to a first threshold temperature higher than a second threshold temperature after starting to drive the first comparator 123; and the voltage source 121 shifts the voltage level of the first threshold voltage Vth1 to a voltage level equivalent to a third threshold temperature lower than the second threshold temperature, on the basis of an output signal of the first comparator 123 when the temperature to be monitored reaches the first threshold temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor integrated circuit device provided with a thermal protection circuit, and more particularly to an improvement in accuracy of the thermal protection function.

  Conventionally, many of the semiconductor integrated circuit devices (hereinafter referred to as IC [Integrated Circuit]) for driving a power transistor such as a power supply device and a motor driving device are ICs (in particular, the power transistor) caused by an abnormal temperature rise of the IC. ) Is mounted (so-called thermal shutdown circuit) (see, for example, Patent Documents 1 and 2 by the applicant of the present application).

  Conventional thermal protection circuits generally use a characteristic that the forward drop voltage between the base and emitter of a bipolar transistor or the forward drop voltage of a diode varies depending on the ambient temperature, and generates a thermal protection signal. It was supposed to be generated.

Further, the conventional thermal protection circuit is generally an automatic return type having a hysteresis at a threshold temperature. At this time, as shown in FIG. 5, the conventional thermal protection circuit compares the first and second threshold voltages Vth1 and Vth2 with the heat generation detection voltage Va corresponding to the monitoring target temperature, and the first and second comparators A4. , A5, and a latch circuit A7 (such as an RS flip-flop) that is set / reset by the output signals thereof, and the output of the latch circuit A7 is set as the thermal protection signal Stsd, thereby providing hysteresis to the threshold temperature. It was supposed to have a configuration.
JP 2004-253936 A Japanese Patent Publication No. 6-16540

  Certainly, with the above-described conventional thermal protection circuit, it is possible to detect and shut off abnormal heat generation of the IC due to malfunction or overload, thereby preventing destruction of the IC.

  However, as described above, the conventional thermal protection circuit is configured to generate a thermal protection signal by latching the output signal of the comparator, and an unintended transition occurs in the output logic of the comparator due to superposition of noise or the like. There is a risk of latching the output logic transition. Therefore, in the conventional thermal protection circuit, when the overheat monitoring target is also a noise source, noise is superimposed on the thermal protection circuit (particularly the power supply voltage application end or output end of the heat generation detection unit) provided in the vicinity of the overheat monitoring target. However, there is a problem that an erroneous thermal protection signal is generated.

  In particular, in recent years, in switching power supply devices and motor drive devices, power transistors that serve as noise sources are often built into ICs, and in such ICs, pulse noise due to on / off of power transistors is superimposed. Therefore, the above-described problem is remarkable, and there is a problem that it is difficult to place the thermal protection circuit in the vicinity of the power transistor that is also an overheat monitoring target.

  In view of the above problems, the present invention provides a thermal protection circuit capable of performing a highly accurate thermal protection operation without depending on superposition of noise or the like, and a semiconductor integrated circuit device including the thermal protection circuit. With the goal.

  In order to achieve the above object, a thermal protection circuit according to the present invention includes a heat generation detection unit that generates a heat generation detection voltage whose voltage level varies according to a monitoring target temperature, and a first that generates a variable first threshold voltage. A DC voltage source; a second DC voltage source that generates a fixed second threshold voltage; a first comparator whose output logic changes according to the level of the heat generation detection voltage and the first threshold voltage; and the heat generation detection A second comparator whose output logic changes according to the level of the voltage and the second threshold voltage, and a thermal protection circuit that sends the output signal of the first comparator to the circuit to be protected as a thermal protection signal The first comparator is driven only when the monitoring target temperature is higher than the second threshold temperature determined by the second threshold voltage based on the output signal of the second comparator, and First straight The voltage source generates a first threshold voltage having a voltage level corresponding to a first threshold temperature higher than the second threshold temperature after the first comparator starts to be driven, and based on an output signal of the first comparator, the monitoring target When the temperature reaches the first threshold temperature, the voltage level of the first threshold voltage is changed to a voltage level corresponding to a third threshold temperature lower than the second threshold temperature (first configuration). . With such a configuration, it is possible to perform a highly accurate thermal protection operation without depending on superposition of noise or the like.

  The thermal protection circuit having the first configuration includes a constant current source that generates a constant current smaller than the drive current of the first comparator; and generates a drive current of the first comparator by mirror-amplifying the constant current. A current mirror circuit that is connected between an output terminal of the constant current source and a ground terminal, and is turned on based on an output signal of the second comparator until the monitored temperature reaches a second threshold temperature, And a switch element that is turned off when the monitored temperature reaches the second threshold temperature (second configuration). With such a configuration, it is possible to reduce power consumption when the first comparator is not driven as much as possible.

  The semiconductor integrated circuit device according to the present invention includes a power transistor that is controlled to be switched, and a thermal protection circuit that detects abnormal heat generation in the power transistor and notifies the protection target circuit of the abnormality. It is preferable that the semiconductor integrated circuit device has a configuration (third configuration) including the thermal protection circuit having the first or second configuration as the thermal protection circuit. With such a configuration, a highly accurate thermal protection operation can be performed without depending on superposition of noise or the like, and the reliability of the semiconductor integrated circuit device can be improved.

  In the semiconductor integrated circuit device having the third configuration, the power transistor may be a switching power supply circuit or a motor drive circuit.

  With the above-described thermal protection circuit according to the present invention, even when the thermal protection circuit is placed in the vicinity of an overheat monitoring target that is a noise generation source, high-precision thermal protection operation is performed without depending on superposition of noise or the like. As a result, it becomes possible to improve the reliability of the semiconductor integrated circuit device having the same.

  Hereinafter, a switching power supply IC will be exemplified and described in detail as a semiconductor integrated circuit device according to the present invention.

  FIG. 1 is a block diagram showing a schematic configuration of a switching power supply IC according to the present invention. As shown in the figure, the switching power supply IC1 includes a thermal protection circuit 10 and a switching power supply circuit 20.

  The thermal protection circuit 10 uses the power supply voltage Vcc supplied via the external terminal T1 as a driving voltage, and the forward drop voltage between the base and emitter of the bipolar transistor and the forward drop voltage of the diode vary depending on the ambient temperature. The thermal protection signal Stsd is generated by utilizing the characteristic of performing.

  The thermal protection signal Stsd is a signal for notifying the protection target circuit (internal circuit or switching power supply circuit 20 not shown) that the chip temperature is abnormal, and is used for shutdown control when the abnormal temperature of the IC rises. Used.

  More specifically, the thermal protection signal Stsd is a binary signal that is asserted (for example, low level transition) when abnormal heat generation occurs and negated (for example, high level transition) when abnormal heat generation does not occur. (See FIG. 4). That is, the protection target circuit that has received the input of the thermal protection signal Stsd from the thermal protection circuit 10 recognizes whether or not abnormal heat generation has occurred according to the assert / negate, and controls the prohibition / permission of the internal operation. Is possible.

  By providing such a thermal protection circuit 10, it is possible to prevent the destruction of the switching power supply IC1 (particularly, the destruction of the power transistor constituting the switching power supply circuit 20) due to abnormal heat generation.

  The thermal protection circuit 10 is provided in the vicinity of the switching power supply circuit 20 (particularly, the power transistor) that is an overheat monitoring target. With such a configuration, it is possible to directly detect the heat generation temperature of the power transistor serving as a heat generation source and to realize a highly accurate heat protection operation.

  The thermal protection circuit 10 is an automatic return type having a hysteresis in the threshold temperature. With such a configuration, when the chip temperature is lowered, it is possible to quickly and spontaneously restore the protection target circuit without waiting for an external return signal. In addition, if the threshold temperature has a hysteresis, the logic oscillation of the thermal protection signal Stsd can be suppressed.

  The internal configuration and operation of the thermal protection circuit 10 will be described in detail later.

  The switching power supply circuit 20 is DC conversion means that converts the power supply voltage Vcc supplied via the external terminal T1 into a desired output voltage Vo and supplies it to an internal circuit (not shown).

  Here, the power transistor constituting the switching power supply circuit 20 is also a noise source that generates switching noise (pulse noise) due to its on / off. For this reason, as described above, switching noise is superimposed on the thermal protection circuit 10 (particularly, high-impedance parts such as the power supply voltage application terminal and the output terminal of the heat generation detection unit) disposed in the vicinity of the switching power supply circuit 20. The situation is easy.

  Therefore, the thermal protection circuit 10 of the present embodiment differs from the conventional configuration of FIG. 5 in order to perform a highly accurate thermal protection operation that does not depend on such superposition of switching noise, and without using a latch circuit, It is set as the structure which produces | generates.

  First, the circuit configuration and operation of the thermal protection circuit 10 will be conceptually described with reference to FIG.

  FIG. 2 is a circuit diagram illustrating a conceptual configuration example of the thermal protection circuit 10. As shown in this figure, the thermal protection circuit 10 of the present embodiment includes a heat generation detection unit 11 that generates a heat generation detection voltage Va whose voltage level varies according to the monitored temperature, and a heat protection signal based on the heat generation detection voltage Va. And a thermal protection signal generation unit 12 for generating Stsd.

  The thermal protection signal generator 12 includes a first DC voltage source 121 that generates a variable first threshold voltage Vth1, a second DC voltage source 122 that generates a fixed second threshold voltage Vth2, a heat generation detection voltage Va, and a first A first comparator 123 whose output logic changes according to the level of the first threshold voltage Vth1, a second comparator 124 whose output logic changes according to the level of the heat generation detection voltage Va and the second threshold voltage Vth2, And is a means for sending the output signal of the first comparator 123 to the protection target circuit as the thermal protection signal Stsd.

  Here, the first comparator 123 is based on the output signal of the second comparator 124 only when the monitoring target temperature exceeds the second threshold temperature (for example, 150 [° C.]) determined by the second threshold voltage Vth2. The first DC voltage source 121 is driven and has a voltage level corresponding to a first threshold temperature (for example, 175 [° C.]) higher than the second threshold temperature after the first comparator 123 starts driving. While the first threshold voltage Vth1 is generated, the voltage level of the first threshold voltage Vth1 is lower than the second threshold temperature when the monitored temperature reaches the first threshold temperature based on the output signal of the first comparator 123. A transition is made to a voltage level corresponding to three threshold temperatures (for example, 125 [° C.]) (see FIG. 4).

  By adopting such a configuration, unlike the conventional configuration of FIG. 5, the threshold temperature can be provided with hysteresis without the need for a latch circuit. Therefore, for example, even when noise is superimposed on the heat generation detection voltage Va and an unintended temporary transition occurs in the output logic of the first comparator 123, the logic state of the thermal protection signal Stsd is not fixed thereby. Therefore, with the thermal protection circuit 10 of the present embodiment, it is possible to perform a highly accurate thermal protection operation without depending on superposition of noise or the like.

  Next, the circuit configuration and operation of the thermal protection circuit 10 will be described more specifically and in detail with reference to FIGS. 3 and 4.

  FIG. 3 is a circuit diagram showing an embodiment of the thermal protection circuit 10. As described above, the thermal protection circuit 10 includes the heat generation detection unit 11 and the thermal protection signal generation unit 12 as its circuit blocks. Further, the thermal protection signal generation unit 12 includes 1 and second DC voltage sources 121 and 122, and first and second comparators 123 and 124.

  The second DC voltage source 122 includes a constant current source I1 and a resistor R1. One end of the resistor R1 (corresponding to the positive terminal of the second DC voltage source 122 that extracts the second threshold voltage Vth2) is connected to the power supply voltage application terminal via the constant current source I1, while the second comparator 124 is inverted. It is also connected to the input terminal (-). The other end of the resistor R1 is grounded.

  The heat generation detection unit 11 includes a constant current source I2 and diodes D1 to D2. One end of the constant current source I2 is connected to the power supply voltage application end, and the other end is connected to the anode of the diode D1 (corresponding to the output end of the heat generation detection unit 11 that extracts the heat generation detection voltage Va). The cathode of the diode D1 is connected to the anode of the diode D2, and the cathode of the diode D2 is grounded. That is, the heat generation detection unit 11 utilizes a characteristic that the Vf (forward voltage drop) of the diodes D1 to D2 varies depending on the ambient temperature (a negative temperature characteristic of about −2 [mV / ° C.]). The heat generation detection voltage Va (voltage signal whose voltage level decreases as the monitoring target temperature increases) is extracted. The output terminal of the heat generation detector 11 is connected to the non-inverting input terminal (+) of the first and second comparators 123 and 124, respectively.

  The first comparator 123 includes resistors R2, R4 to R5, npn bipolar transistors N1 to N6, pnp bipolar transistors P1 to P8, P10, and P12, and a switch element SW1 (N-channel field effect transistor in the present embodiment). And comprising. On the other hand, the first DC voltage source 121 includes a resistor R3, an npn bipolar transistor N5, and pnp bipolar transistors P9 to P11. That is, the transistor N5 and the transistor P10 are both components of the first comparator 123 and are components of the first DC voltage source 121.

  The gate of the transistor SW is connected to the output terminal of the second comparator 124, and is also grounded through the resistor R2. The drain of the transistor SW is connected to the power supply voltage application terminal via the constant current source I3, and is also connected to the collector of the transistor N1. The source and back gate of the transistor SW are both grounded. The bases of the transistors N1 and N2 are connected to each other, and the connection node is connected to the collector of the transistor N1. The emitters of the transistors N1 and N2 are both grounded. The collector of the transistor N2 is connected to the collector of the transistor P1. The bases of the transistors P1 to P4 and the transistor P9 are connected to each other, and the connection node is connected to the collector of the transistor P1. The transistors P1 to P4 and the emitter of the transistor P9 are all connected to the power supply voltage application terminal.

  The collector of the transistor P2 is connected to the emitter of the transistor P5, and is also connected to the base of the transistor P6. The collector of the transistor P3 is connected to the emitters of the transistors P6 and P7. The collector of the transistor P4 is connected to the emitter of the transistor P8, and is also connected to the base of the transistor P7. The collector of the transistor P9 is connected to the base of the transistor P8 corresponding to the inverting input terminal (−) of the first comparator 123, and is also grounded through the resistor R3.

  The base of the transistor P <b> 5 is connected to the output terminal of the heat generation detection unit 11 as the non-inverting input terminal (+) of the first comparator 123. The collector of the transistor P5 is grounded. The collector of the transistor P6 is connected to the collector of the transistor N3. The emitter of the transistor N3 is grounded. The base of the transistor N3 is connected to the base of the transistor N5, and is also connected to its own collector. The collector of the transistor P7 is connected to the collector of the transistor N4. The base of the transistor N4 is connected to its own collector. The emitter of the transistor N4 is grounded. The collector of the transistor P8 is grounded.

  The collector of the transistor N5 is connected to the collector of the transistor P10. The emitter of the transistor N5 is grounded. The gates of the transistors P10 to P12 are connected to each other, and the connection node is connected to the collector of the transistor P10. The emitters of the transistors P10 to P12 are all connected to the power supply voltage application terminal. The collector of the transistor P11 is connected to the base of the transistor P8. The collector of the transistor P12 is connected to the base of the transistor N6, and is also grounded through the resistor R4. The collector of the transistor N6 is connected to the power supply voltage application terminal via the resistor R4, and is also connected to the internal circuit (not shown) and the thermal protection signal input terminal of the switching power supply circuit 20 as the output terminal of the first comparator 123. Yes. The emitter of the transistor N6 is grounded.

  The operation of the thermal protection circuit 10 having the above configuration will be described in detail with reference to FIGS. FIG. 4 is a diagram for explaining the operation of the thermal protection circuit 10.

  In the thermal protection circuit 10 having the above configuration, when the monitoring target temperature does not reach the second threshold temperature (for example, 150 [° C.]), the heat generation detection voltage Va is higher than the second threshold voltage Vth2. Accordingly, the output of the second comparator 124 becomes high level, and the switch element SW is turned on.

  As described above, the switch element SW is turned on until the heat generation detection voltage Va falls below the second threshold voltage Vth2, in other words, until the monitored temperature exceeds the second threshold temperature. In the meantime, the constant current generated by the constant current source I3 is drawn to the ground terminal, so that current mirror circuits (transistors N1 to N2, transistors P1 to P4 that generate drive currents for the first comparator 123 and the first DC voltage source). , And no current flows through the transistor P9).

  As a result, both the first DC voltage source 121 and the first comparator 123 are not driven, and the transistor N6 that constitutes the output stage of the first comparator 123 is turned off. Therefore, the logic of the thermal protection signal Stsd is at a high level (negate state).

  That is, the thermal protection circuit 10 notifies the protection target circuit that the chip temperature is normal by sending out the thermal protection signal Stsd of the logic. The protection target circuit that has received the input of the thermal protection signal Stsd from the thermal protection circuit 10 can detect that the logic is high level, recognize that no abnormal heat has occurred, and perform normal operation. It becomes.

  In the thermal protection circuit 10 of this embodiment, the constant current generated by the constant current source I3 is set to be smaller than the drive current of the first comparator 123, and the constant current is mirror-amplified by the current mirror circuit. Thus, the driving current of the first comparator 123 is generated. With such a configuration, it is possible to reduce power consumption when the first comparator 123 is not driven as much as possible.

  On the other hand, when the monitored temperature rises and exceeds the second threshold temperature, the heat generation detection voltage Va becomes lower than the second threshold voltage Vth2. Accordingly, the output of the second comparator 124 becomes a low level, and the switch element SW is shifted to the off state. As a result, a constant current is supplied from the constant current source I3 to the current mirror circuit described above, and a driving current for the first comparator 123 is generated via the transistors P2 to P4. Thereby, driving of the first comparator 123 is started. In addition, a predetermined current flows into the resistor R3 of the first DC voltage source 121 via the transistor P9, and generation of the first threshold voltage Vth1 is started.

  At this time, the first DC voltage source 121 has a voltage level (that is, a voltage level lower than the second threshold voltage Vth2) corresponding to a first threshold temperature (for example, 175 [° C.]) higher than the second threshold temperature. A first threshold voltage Vth1 (denoted as Vth1 (A) in FIG. 4) is generated. Therefore, unless the monitored temperature reaches the first threshold temperature, the heat generation detection voltage Va remains higher than the first threshold voltage Vth1, and the current mirror circuit (transistor N3, transistor N5, and , No current flows through the transistors P10 to P12). As a result, the transistor N6 remains in the OFF state, and the logic of the thermal protection signal Stsd is maintained at the previous high level (negate state).

  When the temperature to be monitored further rises and reaches the first threshold temperature, the heat generation detection voltage Va reaches the first threshold voltage Vth1. Therefore, a predetermined current flows from the transistor P6 to the resistor R4 through the subsequent current mirror circuit, and the base potential of the transistor N6 rises. As a result, the transistor N6 is turned on, and the logic of the thermal protection signal Stsd is changed to a low level (asserted state).

  That is, the thermal protection circuit 10 notifies the protection target circuit that the chip temperature is abnormal by sending the thermal protection signal Stsd of the logic. The protection target circuit that has received the input of the thermal protection signal Stsd from the thermal protection circuit 10 can detect that the logic is low level, recognize that abnormal heat generation has occurred, and stop its operation. It becomes.

  At this time, in addition to the constant current originally flowing through the transistor P9, the current through the transistor P11 additionally flows through the resistor R3 of the first DC voltage source 121, and the first threshold voltage The voltage level of Vth1 is a voltage level corresponding to a third threshold temperature (for example, 125 [° C.]) lower than the second threshold temperature (that is, a voltage level higher than the second threshold voltage Vth2, that is, Vth1 (B) in FIG. 4). (Notation). Therefore, as a result of the drive of the protection target circuit being shut down due to the assertion transition of the thermal protection signal tsd, the heat generation detection voltage Va remains lower than the first threshold voltage Vth1 even if the monitoring target temperature is slightly lowered. The logic of the thermal protection signal Stsd does not change from the asserted state.

  Further, when the monitoring target temperature decreases and falls below the second threshold temperature, the heat generation detection voltage Va becomes higher than the second threshold voltage Vth2. Accordingly, the output of the second comparator 124 becomes high level, and the switch element SW is turned on. As a result, the constant current generated by the constant current source I3 is again drawn out to the ground terminal, and both the first DC voltage source 121 and the first comparator 123 are returned to the non-driven state. The transistor N6 constituting the output stage is turned off, and the logic of the thermal protection signal Stsd is restored to the high level (negate state).

  As described above, in the thermal protection circuit 10 of the present embodiment, the first comparator 123 determines that the monitored temperature exceeds the second threshold temperature determined by the second threshold voltage Vth2 based on the output signal of the second comparator 124. The first DC voltage source 121 is driven only when the first comparator 123 is driven, and the first threshold voltage having a voltage level corresponding to the first threshold temperature higher than the second threshold temperature after the first comparator 123 starts driving. While generating Vth1, on the basis of the output signal of the first comparator 123, when the monitoring target temperature reaches the first threshold temperature, the voltage level of the first threshold voltage Vth1 is lower than the second threshold temperature. Transition to a voltage level corresponding to.

  By adopting such a configuration, unlike the conventional configuration of FIG. 5, the threshold temperature can be provided with hysteresis without the need for a latch circuit. Therefore, for example, even when noise is superimposed on the heat generation detection voltage Va and an unintended temporary transition occurs in the output logic of the first comparator 123, the logic state of the thermal protection signal Stsd is not fixed thereby. Therefore, with the thermal protection circuit 10 of the present embodiment, it is possible to perform a highly accurate thermal protection operation without depending on superposition of noise or the like.

  In the above embodiment, the case where the present invention is applied to the switching power supply IC has been described as an example. However, the application target of the present invention is not limited to this, and other devices such as a motor driving device may be used. The present invention can be widely applied to semiconductor integrated circuit devices.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  The present invention is a technique useful for increasing the thermal protection accuracy of a semiconductor integrated circuit device. For example, a power transistor serving as a noise source is built in an IC, and heat is higher than that of other semiconductor integrated circuit devices. It can be suitably used for a switching power supply device and a motor drive device that are easily generated and require high reliability.

These are block diagrams which show the outline of the switching power supply IC which concerns on this invention. FIG. 2 is a circuit diagram showing a conceptual configuration example of a thermal protection circuit 10. FIG. 3 is a circuit diagram illustrating a specific configuration example of the thermal protection circuit 10. FIG. 6 is a diagram for explaining the operation of the thermal protection circuit 10. These are circuit diagrams which show one prior art example of the thermal protection circuit 1. FIG.

Explanation of symbols

1 Switching power supply IC
DESCRIPTION OF SYMBOLS 10 Thermal protection circuit 20 Switching power supply circuit T1 Power supply terminal 11 Heat generation detection part 12 Thermal protection signal generation part 121 DC voltage source (variable)
122 DC voltage source (fixed)
123 First comparator (for 175 ° C detection)
124 Second comparator (for 150 ° C detection)
I1 to I3 Constant current source D1 to D2 Diode R1 to R5 Resistance N1 to N6 npn type bipolar transistor P1 to P12 pnp type bipolar transistor SW Switch element (N channel field effect transistor)

Claims (4)

  A heat generation detection unit that generates a heat generation detection voltage whose voltage level varies according to the temperature to be monitored, a first DC voltage source that generates a variable first threshold voltage, and a second DC that generates a fixed second threshold voltage A voltage source, a first comparator whose output logic changes according to the level of the heat generation detection voltage and the first threshold voltage, and its output logic changes according to the level of the heat generation detection voltage and the second threshold voltage A thermal protection circuit that sends an output signal of the first comparator to the protection target circuit as a thermal protection signal, the first comparator based on the output signal of the second comparator The monitoring target temperature is driven only when the temperature exceeds the second threshold temperature determined by the second threshold voltage, and the first DC voltage source is the second voltage after the first comparator starts driving. Threshold A first threshold voltage having a voltage level corresponding to a first threshold temperature higher than the first threshold temperature, and when the monitored temperature reaches the first threshold temperature based on the output signal of the first comparator, A thermal protection circuit, wherein the voltage level of the voltage is shifted to a voltage level corresponding to a third threshold temperature lower than the second threshold temperature.   A constant current source that generates a constant current smaller than the drive current of the first comparator; a current mirror circuit that generates a drive current of the first comparator by mirror-amplifying the constant current; and an output terminal of the constant current source and ground And is turned on until the temperature to be monitored reaches the second threshold temperature based on the output signal of the second comparator, and turned off when the temperature to be monitored reaches the second threshold temperature. The thermal protection circuit according to claim 1, further comprising:   A semiconductor integrated circuit device having a built-in power transistor that is switching-controlled and a thermal protection circuit that detects abnormal heat generation of the power transistor and notifies the protection target circuit of an abnormality. A semiconductor integrated circuit device comprising the thermal protection circuit according to claim 1 or 2 as a circuit.   4. The semiconductor integrated circuit device according to claim 3, wherein the power transistor constitutes a switching power supply circuit or a motor drive circuit.

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