JP2005268703A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which has an n-channel MOSFET that could show a high-temperature abnormal operation, and a heat protection circuit capable of detecting an abnormal temperature accurately for a heat protection operation for the n-channel MOSFET. <P>SOLUTION: The semiconductor device has the heat protection circuit supplied with power voltage from a power supply 30. The heat protection circuit comprises a reference voltage source 31, a constant current source 2a that is a load circuit, a transistor 51 for heat protective detection which has a collector connected to the power supply 30, a base connected to the reference voltage source 31, and an emitter connected to the constant current source 2a, and is arranged near the n-channel MOSFET 52, and a comparator 1a which compares the emitter voltage of the transistor 51 with a voltage given by dividing a reference voltage VREF via resistances. The heat protection circuit secures a collector current for the transistor 51 for heat protective detection, and fixes the collector voltage of the transistor 51 to the power voltage. As a result, an abnormal temperature at the n-channel MOSFET 52 is detected accurately without receiving an effect of a parasitic element to enable a heat protection operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor device having an n-channel MOSFET and its thermal protection circuit that can cause abnormal operation at high temperature.

  In recent years, in semiconductor devices, a thermal protection circuit has been added in order to prevent circuit destruction and deterioration in reliability due to abnormal operation at high temperature.

  As a conventional thermal protection circuit, a thermal protection circuit as shown in FIG. Hereinafter, a conventional thermal protection circuit described in Patent Document 1 will be described with reference to FIG. In FIG. 3, reference numeral 30 denotes a power source, 1 denotes a control circuit, and 2 denotes a constant current source. The constant current source 2 includes a current mirror composed of transistors 21 to 24. VOUT is an output terminal of the control circuit 1, and an output voltage VOUT is output. Reference numerals 3 and 4 denote bias resistors that resistance-divide the reference voltage value VREF input from the reference voltage source 31 and turn off the transistor 51 at room temperature. The resistance values are R3 and R4, respectively. Reference numerals 11 and 12 denote base resistors connected to the npn transistors 9 and 10, respectively. Reference numeral 13 denotes a resistor that determines the current value of the constant current source 2. Reference numeral 25 denotes a resistor that determines a current flowing through the diode 14. The transistor 51 is for thermal protection detection, and the transistor 9 is for a buffer. The transistor 10 is for shutting down the control circuit 1 connected to the collector when turned on.

  First, the operation of the thermal protection circuit at normal temperature will be described. In this thermal protection circuit, the thermal protection detection transistor 51 is divided by a reference voltage bias resistor 3 and 4 and biased to a base-emitter voltage that can be turned off at room temperature so as not to affect the normal operation of the control circuit 1. Has been. Therefore, at room temperature, the transistor 51 for thermal protection detection is off, so that the transistor 8 is on and the transistors 9 and 10 are off. Since the collector current of the transistor 10 does not flow when the transistor 10 is in the OFF state, the control circuit 1 operates normally, and the output voltage VOUT having a normal value is output, allowing the operation of the circuit to be thermally protected. To do. Since the collector current does not flow when the transistor 9 is in the OFF state, the collector current of the transistor 23 flows through the diode 14 to the collector of the thermal protection detection transistor 51.

  Next, a state where the ambient temperature rises to an abnormal temperature and the thermal protection circuit operates will be described. Since the base-emitter voltage at which the thermal protection detecting transistor 51 can be turned on has a negative temperature characteristic, the voltage drops by the resistance division of the reference voltage bias resistors 3 and 4 [VREF]. When R4 / (R3 + R4)] is reached, the thermal protection detection transistor 51 is turned on, the transistor 8 is turned off, and the transistors 9 and 10 are turned on. When the transistor 10 is turned on, the collector current of the transistor 10 flows, so that the control circuit 1 is shut down, the output voltage VOUT is lowered to around 0 V, and the circuit to be thermally protected is shut down. When the transistor 9 is on, the collector current of the transistor 23 does not pass through the diode 14 and becomes the collector current of the transistor 9.

  Further, an operation in which the temperature is lowered and the thermal protection circuit is released will be described. Before the release, the thermal protection detection transistor 51 is on, the transistor 8 is off, and the transistors 9 and 10 are on. The control circuit 1 is shut down, and the output voltage VOUT drops to near 0V. Similarly, when the transistor 9 is in the ON state, the collector current of the transistor 23 becomes the collector current of the transistor 9 without passing through the diode D1 (14). As the temperature falls, the base-emitter voltage that can be turned on of the thermal protection detecting transistor 51 has a negative temperature coefficient, and thus rises, and the reference voltage VREF is divided by the bias resistors R3 and R4 [VREF · When R4 / (R3 + R4)] is reached, the thermal protection detection transistor 51 is turned off, the transistor 8 is turned on, and the transistors 9 and 10 are turned off. When the transistor 10 is in the off state, the collector current does not flow, so that the control circuit 1 performs a normal operation, and the normal output voltage VOUT is output. When the transistor 9 is turned off, the collector current of the transistor 23 flows through the diode 14 to the collector of the thermal protection detection transistor 51.

As described above, according to the thermal protection circuit of Patent Document 1, the collector current to the transistor 10 varies depending on the on / off state of the transistor 9, and thus, the base when the thermal protection detection transistor 51 is turned on and off is changed. -The voltage between the emitters can be changed to provide a temperature hysteresis width.
Japanese Patent Application Laid-Open No. 6-121452

  However, the configuration of the thermal protection circuit configured as described above has a problem that heat detection becomes inaccurate when the thermal protection circuit is an n-channel MOSFET. FIG. 4 shows a circuit when the conventional thermal protection circuit is applied to the thermal protection of the n-channel MOSFET. In FIG. 4, reference numeral 52 denotes an n-channel MOSFET. A voltage Vg1 is applied to the gate of the n-channel MOSFET 52, the source is grounded, and the drain is an inductor L7 and the p-channel MOSFET 6 whose other is connected to the load 40. Connected to the drain. A voltage Vg <b> 2 is applied to the gate of the p-channel MOSFET 6, and the source is connected to the power supply 30.

  FIG. 5A is a diagram in which the vicinity of the thermal protection detection transistor 51 and the n-channel MOSFET 52 shown by the portion 5 surrounded by a two-dot chain line in FIG. 4 is extracted, and FIG. It is a figure which shows the cross-section of (a). In FIG. 5A, reference numeral 51 denotes a thermal protection detection transistor, and the emitter of the thermal protection detection transistor 51 is grounded. 52 is an n-channel MOSFET, the source of the n-channel MOSFET 52 is grounded, and the voltage Vg1 is applied to the gate.

  Since the n-channel MOSFET 52 is a thermal protection circuit, the n-channel MOSFET 52 is disposed close to the thermal protection detection transistor 51. As shown in FIG. 5B, a p-type semiconductor is used as a substrate (P-SUB in the figure), and a thermal protection detection transistor 51, which is an npn transistor, is formed in an n-type semiconductor well (NW in the figure). An n-channel MOSFET 52 is formed in the vicinity thereof. However, when the n-channel MOSFET 52 is arranged in the vicinity of the thermal protection detection transistor 51, as shown in FIGS. 5A and 5B, the P-SUB is used as a base, and the thermal protection detection transistor 51 A parasitic npn transistor 53 is generated with the collector as the collector and the drain of the n-channel MOSFET 52 as the emitter. Normally, the P-SUB is grounded, and the base-emitter of the parasitic transistor 53 is called a body diode connected in antiparallel between the drain and source of the n-channel MOSFET 52.

  In FIG. 4, the p-channel MOSFET 6 and the n-channel MOSFET 52 are alternately turned on and off, and a current is supplied to the load 40 via the inductor 7 to supply power. When the p-channel MOSFET 6 is in the on state, the magnetic energy stored in the inductor 7 starts to be released when the p-channel MOSFET 6 is turned off. At this time, the n-channel MOSFET 52 is turned on after a slight delay time in order to avoid simultaneous ON with the p-channel MOSFET 6. During this delay time, a period in which the body diode of the n-channel MOSFET 52 is conducted occurs. That is, a current flows through the base-emitter of the parasitic transistor 53, and the parasitic transistor 53 is turned on. As a result, the current supplied from the constant current source 2 is divided into the collector current of the thermal protection detection transistor 51 and the collector current of the parasitic transistor 53, and the collector current of the parasitic transistor 53 flows to the drain of the n-channel MOSFET 52.

  In the thermal protection circuit using the negative temperature characteristic of the base-emitter voltage of the thermal protection detection transistor 51, the detection temperature can be adjusted by adjusting the collector current of the thermal protection detection transistor 51, Although it has been possible to provide temperature hysteresis as in Document 1, if the collector current of the thermal protection detection transistor 51 becomes unadjustable as described above, these functions are impaired.

  Further, when the parasitic transistor 53 is turned on and a current larger than the current supplied from the constant current source 2 flows from the collector of the thermal protection detection transistor 51 to the drain of the n-channel MOSFET 52, the collector potential of the thermal protection detection transistor 51 is increased. Will fall and cause a malfunction such as causing a thermal protection operation even if the temperature is not abnormal.

  As described above, in the case of a semiconductor device including an n-channel MOSFET in which a body diode may be conducted, a thermal protection circuit using the n-channel MOSFET as a thermal protection circuit can be disposed in the vicinity of the thermal protection circuit. However, there is a problem that it is difficult to accurately detect the thermal protection of the heat protection circuit.

  In view of the above problems, an object of the present invention is to provide a thermal protection circuit in which a malfunction due to a parasitic transistor being turned on can be prevented, and a thermal protection detection transistor can be disposed in the vicinity of a thermal protection circuit. .

  In order to achieve the above object, a semiconductor device of the present invention includes a reference voltage source, a load circuit, a collector connected to a power source, a base connected to the reference voltage source, an emitter connected to the load circuit, It has a thermal protection circuit having an npn transistor installed in the vicinity of the n-channel MOSFET and a comparator for comparing the emitter voltage of the transistor with a predetermined voltage.

  The load circuit of the thermal protection circuit may be a constant current source. The predetermined voltage of the thermal protection circuit may be obtained by dividing the voltage of the reference voltage source. Furthermore, the collector of the npn transistor of the thermal protection circuit may be connected to a power source provided separately from the power source.

  According to the present invention having the above-described configuration, the current flowing through the thermal protection detection transistor is not affected by the parasitic transistor being turned on, and the thermal protection circuit can be prevented from malfunctioning. For this reason, the transistor for thermal protection detection can be disposed in the vicinity of the n-channel MOSFET that is the thermal protection element, and the abnormal temperature of the n-channel MOSFET can be accurately detected to perform the thermal protection operation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a thermal protection circuit according to an embodiment of the present invention. In FIG. 1, reference numeral 1a denotes a comparator. When the output of the comparator 1a is at L level, normal operation is performed, and when the output is H level, thermal protection is performed. Reference numeral 2a denotes a constant current source that allows a constant current I2 to flow. Reference numeral 51 denotes a thermal protection detection transistor. The base of the thermal protection detection transistor 51 is connected to the reference voltage source 31, the collector is connected to the power supply 30, and the emitter is connected to the non-inverting input terminal of the constant current source 2a and the comparator 1a. Has been. Reference numerals 3 and 4 are divided resistors for resistance-dividing the reference voltage value VREF input from the reference voltage source 31 and determining a voltage input to the inverting input terminal of the comparator 1a. The respective resistance values are R3 and R4. To do. Reference numeral 52 denotes an n-channel MOSFET. A voltage Vg1 is applied to the gate of the n-channel MOSFET 52, the source is grounded, and the drain is connected to the inductor 7 connected to the load 40 and the drain of the p-channel MOSFET 6. Has been. A voltage Vg2 is applied to the gate of the p-channel MOSFET 6, and the source is connected to the power supply.

First, the operation of the thermal protection circuit at normal temperature will be described. In the thermal protection circuit of FIG. 1, a reference voltage value VREF is applied to the base of the thermal protection detection transistor 51 and is biased to a base-emitter voltage Vbe that is always on. Therefore, (VREF−Vbe) is applied to the non-inverting input terminal of the comparator 1a. A voltage obtained by dividing the reference voltage value VREF by the dividing resistors 3 and 4, that is, a voltage represented by [VREF · R4 / (R3 + R4)] is applied to the inverting input terminal of the comparator 1a. At normal temperature, the following equation (Equation 1) is established and the output voltage of the comparator 1a is set to L level.
(Equation 1)
VREF−Vbe <VREF · R4 / (R3 + R4)
That is, it is set so as not to affect the normal operation at normal temperature, and at the normal temperature, the L level is output from the comparator 1a to permit the operation of the circuit to be thermally protected.

Next, a state where the ambient temperature rises to an abnormal temperature and the thermal protection circuit operates will be described. The emitter voltage of the thermal protection detection transistor 51 input to the non-inverting input terminal of the comparator 1a is because the base-emitter voltage Vbe that can be turned on by the thermal protection detection transistor 51 has a negative temperature characteristic. It decreases with increasing temperature. When an abnormal temperature is reached and the operating temperature limit is exceeded, the voltage input to the inverting input terminal of the comparator 1a exceeds the potential of the inverting input terminal and is given by the following equation (Equation 2). Is inverted to H level, and the signal to be thermally protected is shut down by the signal.
(Equation 2)
VREF−Vbe> VREF · R4 / (R3 + R4)
Conversely, when the ambient temperature falls from a value equal to or higher than the limit value of the operating temperature, the non-inverting input terminal of the comparator 1a is increased by the rise of the base-emitter voltage Vbe of the thermal protection detection transistor 51 at the same ambient temperature. And the voltage of the inverting input terminal falls below the voltage of the inverting input terminal, and the output of the comparator 1a is inverted to the L level. As a result, the shutdown of the circuit is canceled and the circuit can be restarted.

  2A is a diagram in which the vicinity of the thermal protection detection transistor 51 and the n-channel MOSFET 52 in the thermal protection circuit, which is shown by the portion 5 surrounded by a two-dot chain line in FIG. 1, is extracted, and FIG. It is a figure which shows the cross-section of (a). In FIG. 2A, reference numeral 51 denotes a thermal protection detection transistor. An n-channel MOSFET 52 has a source grounded and a voltage Vg1 applied to the gate. Since the n-channel MOSFET 52 is a thermal protection circuit, the n-channel MOSFET 52 is arranged close to the thermal protection detection transistor 51. As shown in FIG. 2B, a p-type semiconductor is used as a substrate (P-SUB in the figure), and a thermal protection detection transistor 51, which is an npn transistor, is formed in an n-type semiconductor well (NW in the figure). An n-channel MOSFET 52 is formed in the vicinity thereof.

  By the way, when the n-channel MOSFET 52 is disposed in the vicinity of the thermal protection detection transistor 51, as shown in FIGS. 2A and 2B, the P-SUB is used as a base, and the thermal protection detection transistor 51 A parasitic npn transistor 53 is generated with the collector as the collector and the drain of the n-channel MOSFET 52 as the emitter.

  In FIG. 1, a p-channel MOSFET 6 and an n-channel MOSFET 52 are alternately turned on and off, and a current is supplied to the load 40 via the inductor 7 to supply power. When the p-channel MOSFET 6 is in the on state, the magnetic energy stored in the inductor 7 starts to be released when the p-channel MOSFET 6 is turned off. At this time, the n-channel MOSFET 52 is turned on after a slight delay time in order to avoid simultaneous ON with the p-channel MOSFET 6. During this delay time, the drain potential of the n-channel MOSFET 52 becomes lower than the substrate potential (ground potential) by the induced voltage of the inductor 7 and becomes a negative potential. At this time, a current flows through the base-emitter of the parasitic transistor 53, and the parasitic transistor 53 is turned on.

  At this time, a current flows from the collector of the thermal protection detection transistor 51 to the drain of the n-channel MOSFET 52 via the parasitic transistor 53. However, the current flowing from the collector to the emitter of the thermal protection detection transistor 51 is set by the constant current source 2 a connected to the emitter of the thermal protection detection transistor 51 and is not affected by the parasitic transistor 53. Further, since the collector of the thermal protection detection transistor 51 is connected to the power supply, the collector potential of the thermal protection detection transistor 51 does not vary from the power supply voltage. That is, the thermal protection detection transistor 51 is not affected by the on / off of the parasitic transistor 53 and does not malfunction.

The temperature at which the output of the comparator 1a is inverted is adjusted by the current value I2 of the constant current source 2a because the base-emitter voltage Vbe that can be turned on by the transistor is expressed by the following equation (Equation 3). It turns out that it is possible.
(Equation 3)
Vbe = (k · T / q) ln [I2 / Is]
In the above-described embodiment, the temperature at which the thermal protection operation is performed as an abnormal temperature due to the increase in the ambient temperature and the temperature at which the thermal protection operation is canceled due to the decrease in the ambient temperature have been described as being equal, but depending on the configuration of the constant current source 2a Temperature hysteresis can be provided. For example, the output of the comparator 1a is detected, and the constant current value of the constant current source 2a when the output of the comparator 1a is at the H level may be set to be smaller than the constant current value when it is at the L level.

  Further, although the constant current source 2a is used for setting the current flowing through the thermal protection detection transistor 51, this is not limited to the constant current source, and may be a resistor, for example. When this resistance value is r, the current flowing through the thermal protection detection transistor 51 is represented by (VREF−Vbe) / r.

  Furthermore, the reference voltage VREF of the reference voltage source 31 used in the present embodiment is better as the fluctuation due to temperature is smaller. In addition, the voltage applied to the inverting input terminal of the comparator 1a is generated by resistance division from the reference voltage VREF. However, the present invention is not limited to this method. For example, another reference voltage source may be used. In this case, it is desirable that another reference voltage source has a small variation due to temperature as described above. Alternatively, when the reference voltage VREF of the reference voltage source 31 has temperature characteristics, by using another reference voltage source having a temperature characteristic opposite to that of the reference voltage source 31 for the voltage applied to the inverting input terminal, The characteristics should be offset.

  In the embodiment of the present invention, the collector of the thermal protection detection transistor 51 is connected to the power supply 30, but may be connected to another power supply. Since the thermal protection detection transistor 51 and the parasitic transistor 53 share the collector in structure, the collector current that flows when the parasitic transistor 53 is turned on should not affect the operation of the thermal protection detection transistor 51. . That is, the collector shared by both transistors 51 and 53 only needs to be connected to a power supply having sufficient current supply capability.

  As described above, the present invention fixes the collector potential of the thermal protection detection transistor even if a current flows through the parasitic transistor between the thermal protection detection transistor and the n-channel MOSFET built in the semiconductor device. Since it can prevent malfunction of the transistor for thermal protection detection, the thermal protection circuit can be arranged in the vicinity of the power element, and a thermal protection circuit capable of accurately detecting the thermal protection of the power element can be realized. It is.

  As described above, the present invention is useful for a semiconductor device having an n-channel MOSFET that can cause abnormal operation at high temperature and a thermal protection circuit thereof.

The circuit diagram of the thermal protection circuit in one embodiment of the present invention Explanatory drawing of the transistor 51 for thermal protection detection and the n-channel MOS 52 in FIG. Circuit diagram of conventional thermal protection circuit Circuit diagram when a conventional thermal protection circuit is applied as a thermal protection circuit with a switching element connected by an inductor connected to a load 40 Explanatory drawing of the transistor 51 for thermal protection detection and the n-channel MOS 52 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control circuit 1a Comparator 2, 2a Constant current source 3, 4 Bias resistance 5 Thermal protection detection transistor 51 and n channel MOS 52
6 p-channel MOS
7 Inductors 8, 9, 10 npn transistors 11, 12, 13, 25 Resistor 14 Diode 30 Power supply 31 Reference voltage source 40 Load 51 Thermal protection detection transistor 52 n-channel MOS
53 Parasitic transistor

Claims (4)

A semiconductor device having an n-channel MOSFET and a thermal protection circuit,
The thermal protection circuit has a reference voltage source, a load circuit, a collector connected to a power source, a base connected to the reference voltage source, an emitter connected to the load circuit, and is installed in the vicinity of the n-channel MOSFET. A semiconductor device comprising an npn transistor and a comparator for comparing an emitter voltage of the transistor with a predetermined voltage.   2. The semiconductor device according to claim 1, wherein the load circuit of the thermal protection circuit is a constant current source.   2. The semiconductor device according to claim 1, wherein the predetermined voltage of the thermal protection circuit is obtained by dividing the voltage of the reference voltage source.   The semiconductor device according to claim 1, wherein a collector of the npn transistor of the thermal protection circuit is connected to a power source provided separately from the power source.

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