JP2013066085A - Overcurrent protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent protection circuit that can cancel the effect of temperature characteristics of an overcurrent detection resistance.SOLUTION: A first junction of a reference resistance and a first constant current source is connected with a second constant current source for supplying a second constant current having positive temperature characteristics to the first junction such that temperature characteristics of a potential at the first junction become equal to temperature characteristics of a potential at a voltage detection terminal of an overcurrent detection resistance. The second constant current source has: a third constant current source for supplying a third constant current having negative temperature characteristics; a fourth constant current source for supplying a fourth constant current having no temperature characteristics; a first current mirror circuit comprising a first transistor connected in series with the third constant current source and a second transistor connected in series with the fourth constant current source; and a current path connected to a junction of the fourth constant current source and the second transistor to supply the second constant current to the first junction. The third constant current source is formed on the same substrate as the overcurrent detection resistance.

Description

  The present invention has an overcurrent detection resistor having a positive temperature characteristic and connected in series with a switching element that controls supply of power to a load between a power supply and a ground. The present invention relates to an overcurrent protection circuit that detects a potential difference generated in a resistor by a comparator and controls on / off of a switching element.

  Conventionally, power supply to a load disposed between a power supply and a ground is controlled by turning on / off switching elements connected in series to the load. Further, for example, Non-Patent Document 1 discloses an overcurrent protection circuit that turns off a switching element when an overcurrent flows to prevent the overcurrent from flowing to the switching element, and hence the load.

  In this overcurrent protection circuit, an overcurrent detection resistor (current detection device Z1 in FIG. 4.66 of Non-Patent Document 1) is connected in series between the power source and the ground, and the overcurrent detection resistor is connected to the overcurrent detection resistor. The generated potential difference is fed back to the control circuit to control on / off of the switching element. Thus, since the overcurrent detection resistor connected in series to the switching element is used, it is possible to directly monitor the current flowing through the switching element and thus the load.

Hiroshi Yamazaki, “Applied Technology of Power MOSFET”, 2nd edition, Nikkan Kogyo Shimbun, February 28, 2003, p. 134-135

  In the overcurrent protection circuit described above, a comparator is generally used as the control circuit. As the overcurrent detection resistor, a diffused resistor is generally used to detect overcurrent.

  However, this overcurrent detection resistor has a positive temperature characteristic. For this reason, the resistance value of the overcurrent detection resistor changes according to the temperature, and as a result, the output of the comparator varies. That is, the overcurrent cannot be detected stably.

  In view of the above problems, an object of the present invention is to provide an overcurrent protection circuit that can cancel the influence of temperature characteristics of an overcurrent detection resistor.

In order to achieve the above object, an overcurrent protection circuit according to claim 1 comprises:
An overcurrent detection resistor having a positive temperature characteristic and connected in series with a switching element that controls supply of power to a load between a power supply and a ground;
A reference resistor arranged such that either the power supply side terminals or the ground side terminals have the same potential with respect to the overcurrent detection resistor,
A first constant current source connected to a terminal opposite to a terminal having the same potential as the overcurrent detection resistor in the reference resistor and supplying a first constant current having no temperature characteristic to the reference resistor;
The voltage signal of the terminal opposite to the terminal having the same potential as the reference resistance in the overcurrent detection resistor (hereinafter referred to as the voltage detection terminal of the overcurrent detection resistor) is input to one input terminal, and the other input terminal A comparator to which a voltage signal at a first connection point where the reference resistor and the first constant current source are connected is input,
Based on the output of the comparator, on / off of the switching element is controlled so that power supply to the load is cut off when an overcurrent flows through the overcurrent detection resistor.

The first connection point has a positive temperature characteristic with respect to the first connection point so that the temperature characteristic of the potential of the first connection point is equal to the temperature characteristic of the potential of the voltage detection terminal of the overcurrent detection resistor. A second constant current source is connected to supply a second constant current having
The second constant current source is
A third constant current source for supplying a third constant current having a negative temperature characteristic;
A fourth constant current source for supplying a fourth constant current having no temperature characteristic;
A first current mirror circuit composed of a first transistor connected in series to the third constant current source and a second transistor connected in series to the fourth constant current source;
A current path connected to a connection point between the fourth constant current source and the second transistor, and supplying a second constant current to the first connection point;
The third constant current source is formed on the same substrate as the overcurrent detection resistor.

  Thus, according to the present invention, the current flowing in the current path constituting the second constant current source is obtained by subtracting the third constant current having a negative temperature characteristic from the fourth constant current having no temperature characteristic. Become. Therefore, a current having a positive temperature characteristic flows. In the second constant current source, the current having the positive temperature characteristic is used to make the second temperature characteristic of the potential of the first connection point equal to the temperature characteristic of the potential of the voltage detection terminal of the overcurrent detection resistor. A constant current is formed.

  Further, the third constant current source that supplies the third constant current having the negative temperature characteristic is formed on the same substrate as the overcurrent detection resistor having the positive temperature characteristic. For this reason, the temperature of the overcurrent detection resistor and the temperature of the third constant current source are substantially the same.

  As described above, according to the present invention, the potential of the first connection point, that is, the reference voltage to be compared with the potential of the voltage detection terminal of the overcurrent detection resistor is changed according to the temperature, and the temperature characteristic of the overcurrent detection resistor is changed. The influence can be canceled.

  As described in claim 2, the present invention can be applied to a configuration in which the switching element is arranged on the power supply side with respect to the load.

In this case, the overcurrent detection resistor is disposed on the power supply side with respect to the switching element,
The power supply side terminal of the reference resistor is connected to the power supply side terminal of the overcurrent detection resistor.
The first constant current source is connected to the ground side terminal of the reference resistor,
The voltage signal of the ground side terminal of the overcurrent detection resistor is input to the inverting input terminal of the comparator, and the voltage signal of the first connection point is input to the non-inverting input terminal.

For example, as in claim 3
The second constant current source is
A fifth constant current source for supplying a fifth constant current having no temperature characteristic;
A plurality of first transistors configured by a third transistor connected in series to the fifth constant current source and a plurality of fourth transistors whose terminals on the power supply side are connected to the first connection point and arranged in parallel with each other. 2 current mirror circuit,
The current path may be configured to electrically connect a connection point between the fourth constant current source and the second transistor and a connection point between the fifth constant current source and the third transistor.

  According to this, the positive temperature characteristic (slope) of the second constant current can be set to a desired value depending on the number of the fourth transistors, that is, the second current mirror circuits.

As claimed in claim 4,
Each of the fourth transistors may be configured such that a first trim resistor is connected in series.

  According to this, the resistance value of the first trim resistor is changed by laser trim, and the temperature characteristic of the potential at the first connection point is matched with the temperature characteristic of the potential at the voltage detection terminal of the overcurrent detection resistor. it can. That is, the influence of the temperature characteristic of the overcurrent detection resistor can be canceled with higher accuracy.

As claimed in claim 5,
The second trim resistor may be connected in series to the first constant current source between the first connection point and the ground.

  According to this, by the laser trim, the resistance value of the second trim resistor is changed, whereby the potential at the first connection point is changed in the manufacturing variation of the overcurrent detection resistor at the potential of the voltage detection terminal of the overcurrent detection resistor. Correction can be made by the amount of (variation in resistance value caused by manufacturing). The manufacturing variation is, in other words, an intercept (initial offset) with respect to the inclination.

As claimed in claim 6,
A plurality of first constant current sources arranged in parallel to each other may be connected to the first connection point.

  This also makes it possible to correct manufacturing variations in overcurrent detection resistors depending on the number of first constant current sources.

  On the other hand, as described in claim 7, the present invention can also be applied to a configuration in which the switching element is arranged on the ground side with respect to the load.

In this case, the overcurrent detection resistor is arranged on the ground side with respect to the switching element,
The ground side terminal of the overcurrent detection resistor and the ground side terminal of the reference resistor have the same potential.
The first constant current source is connected to the power supply side terminal of the reference resistor,
The voltage signal of the power supply side terminal of the overcurrent detection resistor is input to the non-inverting input terminal of the comparator, and the voltage signal of the first connection point is input to the inverting input terminal.

For example, as described in claim 8,
The second constant current source is
A fifth constant current source for supplying a fifth constant current having no temperature characteristic;
A second current mirror circuit composed of a third transistor and a fourth transistor connected in series to the fifth constant current source;
Between the power source and the ground, the fifth transistor arranged in series with the fourth transistor on the power source side and the ground side terminal are connected to the first connection point, and a plurality of second transistors arranged in parallel with each other. A plurality of third current mirror circuits composed of six transistors,
The current path may be configured to electrically connect a connection point between the fourth constant current source and the second transistor and a connection point between the fifth constant current source and the third transistor.

  According to this, the positive temperature characteristic (slope) of the second constant current can be set to a desired value by the number of the sixth transistors, that is, the third current mirror circuits.

As claimed in claim 9,
Each fifth transistor may have a third trim resistor connected in series.

  According to this, the resistance value of the third trim resistor is changed by laser trim, and the temperature characteristic of the potential of the first connection point is matched with the temperature characteristic of the potential of the voltage detection terminal of the overcurrent detection resistor. it can. That is, the influence of the temperature characteristic of the overcurrent detection resistor can be canceled with higher accuracy.

As claimed in claim 10,
The first constant current source is
A sixth constant current source for supplying a sixth constant current having no temperature characteristic;
A fourth current mirror circuit configured by a seventh transistor arranged in series with respect to the sixth constant current source and connected in series; and an eighth transistor having a ground-side terminal connected to the first connection point; The structure which has these can be employ | adopted.

As claimed in claim 11,
A fourth trim resistor may be connected in series to at least one of the seventh transistor and the eighth transistor between the first connection point and the power source.

  According to this, by the laser trim, the resistance value of the fourth trim resistor is changed, whereby the potential of the first connection point is changed to the manufacturing variation of the overcurrent detection resistor at the potential of the voltage detection terminal of the overcurrent detection resistor. Correction can be made by the amount of (variation in resistance value caused by manufacturing). The manufacturing variation is, in other words, an intercept (initial offset) with respect to the inclination.

Furthermore, as claimed in claim 12,
A plurality of eighth transistors are arranged in parallel with each other to form a plurality of fourth current mirror circuits,
A fourth trim resistor may be connected in series to each eighth transistor.

  This also makes it possible to correct manufacturing variations in overcurrent detection resistors.

As claimed in claim 13,
Storage means for storing data for correcting manufacturing variations of overcurrent detection resistors;
It is good also as a structure provided with the correction means which correct | amends the voltage signal of a 1st connection point with the data memorize | stored in memory, and inputs it into the input terminal of a comparator.

  Such electrical trimming can also correct manufacturing variations in overcurrent detection resistors.

As claimed in claim 14,
The reference resistor may have a configuration in which a resistor having no temperature characteristic and a resistor having a positive temperature characteristic are connected in series.

  According to this, the configuration of the second constant current source can be simplified.

It is a figure which shows schematic structure of the overcurrent protection circuit which concerns on 1st Embodiment. It is a figure which shows an example of a 3rd constant current source. It is a figure which shows the modification of a 3rd constant current source. It is a figure which shows the modification of a switching element. It is a figure which shows the modification of a switching element. It is a figure which shows the modification of a switching element. It is a figure which shows schematic structure of the overcurrent protection circuit which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the overcurrent protection circuit which concerns on 3rd Embodiment. It is a figure which shows schematic structure of the overcurrent protection circuit which concerns on 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, common or related elements are given the same reference numerals.

(First embodiment)
In this embodiment, an overcurrent protection circuit is mounted on a vehicle, and is applied as an overcurrent protection circuit of a power supply device that supplies power to, for example, a microcomputer as a load.

  Hereinafter, the configuration of the overcurrent protection circuit including the load and the power supply device will be described with reference to FIG. First, a load and a power supply device will be described.

  The switching element 12 shown in FIG. 1 controls the supply of electric power (voltage) to the microcomputer as the load 10. In the present embodiment, an n-channel MOSFET (hereinafter simply referred to as MOS) is employed as the switching element 12. The switching element 12 is formed on the same semiconductor substrate (chip) as the overcurrent protection circuit 30 described later, the source is connected to the output terminal 14 of the chip, and the drain is on the power supply side.

  As shown in FIG. 1, when the load 10 is connected to the output terminal 14, the load 10 is connected to the ground side (low potential side) between the in-vehicle battery + B (hereinafter referred to as a power source) and the ground, and the switching element. The load 10 and the switching element 12 are connected in series with the power source side 12 (high potential side).

  Next, a driver circuit of the switching element 12 in the power supply device will be described. The driver circuit shown in this embodiment is only an example, and various known driver circuits can be applied.

  The output terminal of the operational amplifier 16 is connected to the gate of the MOS constituting the switching element 12. A constant voltage source 18 is connected to the non-inverting input terminal (+) of the operational amplifier 16 so that a predetermined voltage is input. On the other hand, one end of the resistor 20 is connected to the inverting input terminal (−), and the other end of the resistor 20 is connected to the ground. One end of the resistor 22 is connected to the connection point between the inverting input terminal (−) and the resistor 20. The other end of the resistor 22 is electrically connected to the source of the MOS constituting the switching element 12. The resistors 20 and 22 are resistors that do not have temperature characteristics, and are formed using, for example, CrSi or polySi.

  In the power supply device configured as described above, the potential input to the non-inverting input terminal (+) is higher than the potential input to the inverting input terminal (−) (within the resistors 20 and 22) while the power is on. If it is higher than the point potential, the switching element 12 is turned on and power is supplied to the load 10. On the other hand, when the potential input to the non-inverting input terminal (+) becomes lower than the potential input to the inverting input terminal (−), the switching element 12 is turned off and the power supply to the load 10 is cut off. The

  Next, the overcurrent protection circuit 30 will be described.

  The overcurrent protection circuit 30 includes an overcurrent detection resistor 32, a reference resistor 34, a first constant current source 36, a comparator 42, and a second constant current source 50.

  The overcurrent detection resistor 32 has a positive temperature characteristic, and is connected in series with the switching element 12 between the power supply and the ground. In the present embodiment, the overcurrent detection resistor 32 is formed of a diffused resistor formed on a semiconductor substrate, and the resistance value is about several hundreds mΩ to several ohms. Further, it is arranged on the power supply side with respect to the switching element 12, that is, connected to the drain of the switching element 12.

  The reference resistor 34 is arranged so that either the power supply side terminals or the ground side terminals have the same potential with respect to the overcurrent detection resistor 32. In the present embodiment, the power supply side terminal of the reference resistor 34 is connected to the power supply side terminal of the overcurrent detection resistor 32. Further, it is formed using CrSi or polySi, and the resistance value is about several tens of k ohms to several hundreds of k ohms.

  The first constant current source 36 is connected to a terminal of the reference resistor 34 opposite to the terminal having the same potential as that of the overcurrent detection resistor 32, and the first constant current I1 having no temperature characteristic is supplied to the reference resistor. 34 is supplied. In the present embodiment, the first constant current source 36 is connected to the ground side terminal of the reference resistor 34. In addition, the second trim resistor 38 is disposed on the ground side of the first constant current source 36, and between the first connection point 40 where the reference resistor 34 and the first constant current source 36 are connected, and the ground, A second trim resistor 38 is connected in series to the first constant current source 36.

  The comparator 42 receives, at one input terminal, a voltage signal of a terminal opposite to the terminal of the overcurrent detection resistor 32 that has the same potential as the reference resistor 34 (hereinafter, referred to as a voltage detection terminal of the overcurrent detection resistor 32). The voltage signal at the first connection point 40 is input to the other input terminal. In the present embodiment, the voltage signal V1 of the ground side terminal of the overcurrent detection resistor 32 is input to the inverting input terminal (−) of the comparator 42, and the voltage signal of the first connection point 40 is input to the non-inverting input terminal (+). Vref is input. Therefore, when an overcurrent flows through the overcurrent detection resistor 32 and the voltage signal V1 decreases and Vref> V1, the comparator 40 outputs a high signal having a high voltage level, and when Vref <V1, the comparator 40 A low level signal is output.

  The output terminal of the comparator 42 is connected to the base of an npn type bipolar transistor 44. The emitter of the bipolar transistor 44 is connected to the ground, and the collector is connected to the connection point between the output terminal of the operational amplifier 16 constituting the power supply device and the gate of the MOS constituting the switching element 12. Therefore, when an overcurrent flows through the overcurrent detection resistor 32 and a high signal is output from the comparator 42, the transistor 44 is turned on, and the gate of the MOS constituting the switching element 12 is electrically connected to the ground. . As a result, the switching element 12 is turned off, and power supply to the load 10 is interrupted. On the other hand, when a low signal is output from the comparator 42, the transistor 44 is turned off, and the switching element 12 is controlled by the output of the operational amplifier 16.

  Next, the second constant current source 50 will be described. The second constant current source 50 is connected to the first connection point 40 so that the temperature characteristic of the potential V1 of the first connection point 40 is equal to the temperature characteristic of the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. The second constant current I2 having a positive temperature characteristic is supplied. As a result, the current I0 flowing through the reference resistor 34 is the sum (I0 = I1 + I2) of the first constant current I1 having no temperature characteristic and the second constant current I2 having a positive temperature characteristic. Thereby, the temperature characteristic of the potential V1 of the first connection point 40 can be made equal to the temperature characteristic of the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. The second constant current source 50 includes a plurality of constant current sources and a plurality of current mirror circuits.

  Specifically, a third constant current source 52 that supplies a third constant current I3 having negative temperature characteristics, and a fourth constant current source 54 that supplies a fourth constant current I4 having no temperature characteristics, Have. The third constant current source 52 is formed on the same semiconductor substrate as the overcurrent detection resistor 34. A first transistor 56 a is connected in series to the third constant current source 52, and a second transistor 56 b is connected in series to the fourth constant current source 54. The transistors 56a and 56b have the same characteristics, and the transistors 56a and 56b constitute a first current mirror circuit 56.

  In the present embodiment, the third constant current source 52 and the first transistor 56a are connected in series between the power source and the ground, with the third constant current source 52 on the power source side and the first transistor 56a on the ground side. As the first transistor 56a, an npn bipolar transistor is employed, and the emitter is connected to the ground (ground) and the collector is connected to the third constant current source 52. The fourth constant current source 54 and the second transistor 56b are connected in series between the power source and the ground, with the fourth constant current source 54 on the power source side and the second transistor 56b on the ground side. As the second transistor 56b, an npn-type bipolar transistor is employed, and the emitter is connected to the ground (ground) and the collector is connected to the fourth constant current source 54. The bases of the transistors 56a and 56b are connected, and the collector of the first transistor 56a is connected to the base.

  As shown in FIG. 2, the third constant current source 52 that supplies a third constant current I3 having negative temperature characteristics includes a current mirror circuit 70, bipolar transistors 72 and 76, and resistors 74 and 78. The current mirror circuit 70 includes two pnp bipolar transistors 70a and 70b having the same characteristics. The bases of the bipolar transistors 70a and 70b are connected, and the collector of one bipolar transistor 70a is connected to the base. The emitters of the bipolar transistors 70a and 70b are connected to a power source. The collector of the npn bipolar transistor 72 is connected to the collector of the bipolar transistor 70a whose collector is connected to the base. The emitter of the bipolar transistor 72 is connected to one end of a resistor 74, and the other end of the resistor 74 is connected to the ground. The base of an npn bipolar transistor 76 is connected to the connection point between the emitter of the bipolar transistor 72 and the resistor 74. The bipolar transistor 76 has an emitter connected to the ground and a collector connected to one end of the resistor 78. The other end of the resistor 78 is connected to a power source. The base of the bipolar transistor 72 is connected to the connection point between the collector of the bipolar transistor 76 and the resistor 78. The resistors 74 and 78 are resistors having no temperature characteristics, and are formed using, for example, CrSi or polySi.

  The collector of the first transistor 56a constituting the first current mirror circuit 56 is connected to the emitter of the other bipolar transistor 70b constituting the current mirror circuit 70.

  The third constant current source 52 thus configured has a temperature characteristic in which the forward voltage Vf (base-emitter voltage) of the diode formed between the base and emitter of the bipolar transistor 76 is negative. For this reason, when the resistance value of the resistor 74 is R, the current Ie shown in FIG. 2 is Ie = Vf / R, which indicates a negative temperature characteristic. Further, the current mirror circuit 70 causes the third constant current I3 to be I3 = Ie. Therefore, the third constant current I3 has a negative temperature characteristic.

  The second constant current source 50 also includes a fifth constant current source 58 that supplies a fifth constant current I5 that does not have temperature characteristics, and a third transistor 60a that is connected in series to the fifth constant current source 58. The power supply side terminal is connected to the first connection point 40, and has a plurality of second current mirror circuits 60 constituted by a plurality of fourth transistors 60b arranged in parallel with each other.

  In the present embodiment, the fifth constant current source 58 and the sixth transistor 60a are connected in series between the power source and the ground, with the fifth constant current source 58 as the power source side and the third transistor 60a as the ground side. The third transistor 60a is an npn-type bipolar transistor, and has an emitter connected to the ground (ground) and a collector connected to the fifth constant current source 58. The base of the third transistor 60a is connected to the base of the fourth transistor 60b, and this base is connected to the collector.

  A connection point between the fourth constant current source 54 and the second transistor 56 b and a connection point between the fifth constant current source 58 and the third transistor 60 a are electrically connected by a current path 62. The current path 62 is a path that is connected to the connection point between the fourth constant current source 54 and the second transistor 56 b and supplies the second constant current I 2 to the first connection point 40. In the present embodiment, a diode 62 a is inserted in the current path 62. The diode 62a is arranged with the anode on the second constant current source 54 side and the cathode on the third constant current source 58 side, and current flows from the fifth constant current source 58 side to the second constant current source 54 side. Is supposed to prevent.

  By this current path 62, the fourth constant current I4 supplied from the fourth constant current source 54 is divided between the second transistor 56b side and the current path 62 side. The current Ia divided by the first current mirror circuit 56 toward the second transistor 56b is Ia = I3. That is, it has a negative temperature characteristic. On the other hand, the current Ib divided to the current path 62 side is Ib = (I4-Ia). As described above, since the current Ia has a negative temperature characteristic, the current Ib has a positive temperature characteristic.

  As the fourth transistor 60b, an npn-type bipolar transistor is adopted. In the present embodiment, two fourth transistors 60 b are provided, and both of the fourth transistors 60 b are connected to the ground side and the collector to the first connection point 40. The base is connected to the base of the third transistor 60a described above. The first trim resistor 64 is connected in series to the emitter of each transistor 60b, and the other end of the first trim resistor 64 is connected to the ground. As described above, the plurality of (two) fourth transistors 60b are arranged in parallel between the first connection point 40 and the ground. The characteristics of the fourth transistor 60b and the third transistor 60a are equal to each other, and the second current mirror circuit 60 is configured between each of the fourth transistor 60b and the third transistor 60a.

  The current Ic flowing through the third transistor 60a is the sum of the fifth constant current I5 and the current Ib flowing through the current path 62, that is, Ic = (I5 + Ib). The current Id flowing through each fourth transistor 60b by the second current mirror circuit 60 is Id = Ic. Therefore, the second constant current I2 is Id × the number of the fourth transistors 60b (the number of the second current mirror circuits 60). In this embodiment, I2 = Id × 2.

  Next, the effect of the characteristic part of the overcurrent protection circuit 30 of this embodiment applied to the power supply device will be described.

  In the present embodiment, the current Ib flowing through the current path 62 constituting the second constant current source 50 substantially has a third constant current I3 having a negative temperature characteristic from the fourth constant current I4 having no temperature characteristic. (= Ia) is subtracted. Thus, the current Ib has a positive temperature characteristic. In the second constant current source 50, using the current Ib having the positive temperature characteristic, the temperature characteristic of the potential Vref at the first connection point 40 is equal to the temperature characteristic of the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. A second constant current I2 that is equal is formed.

  The third constant current source 52 that supplies the third constant current I3 having negative temperature characteristics is formed on the same semiconductor substrate as the overcurrent detection resistor 32 having positive temperature characteristics. For this reason, the temperature of the overcurrent detection resistor 32 and the temperature of the third constant current source 52 are substantially the same.

  Therefore, the potential Vref at the first connection point 40 to be compared with the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32 is changed according to the temperature as in the case of the potential V1, and the influence of the temperature characteristics of the overcurrent detection resistor 32 is affected. Can be canceled.

  At this time, the positive temperature characteristic (slope) of the second constant current I2 can be set to a desired value depending on the number of the fourth transistors 60b, that is, the second current mirror circuits 60.

  In the present embodiment, the first trim resistor 64 is connected to the emitter of the fourth transistor 60 b constituting the first current mirror circuit 60. According to this, by changing the resistance value of the first trim resistor 64 by laser trim, the temperature characteristic of the potential Vref at the first connection point 40 is changed to the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. It can be adjusted to the temperature characteristics. That is, the influence of the temperature characteristic of the overcurrent detection resistor 32 can be canceled with higher accuracy.

  In the present embodiment, the second trim resistor 38 is connected to the ground side of the first constant current source 36. According to this, by changing the resistance value of the second trim resistor 38 by laser trim, the potential Vref at the first connection point 40 is detected at the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. It is possible to correct the manufacturing variation of the resistor 32 (resistance value variation caused by the manufacturing). The manufacturing variation is, in other words, an intercept (initial offset) with respect to the inclination.

(Modification)
Although not shown in the drawings in addition to the above embodiment, a plurality of first constant current sources 36 may be arranged in parallel between the first connection point 40 and the ground. Also by this, the manufacturing variation of the overcurrent detection resistor 32 can be corrected by the number of the first constant current sources 36.

  As shown in FIG. 3, the resistor 74 constituting the third constant current source 52 may have a configuration in which a resistor 74a having no temperature characteristic and a resistor 74b having a positive temperature characteristic are connected in series. A resistor formed using CrSi or polySi can be used as the resistor 74a, and a diffused resistor can be used as the resistor 74b. When the resistance values of the resistors 74a and 74b are R1 and R2, respectively, Ie = Vf / (R1 + R2), and the negative temperature characteristic (slope) of the current Ie is the resistance 74 that does not have the above-described temperature characteristic (FIG. This is different from the case of only the resistor 74a.

  In the above embodiment, an example in which an n-channel MOS is used as the switching element 12 has been described. However, the switching element 12 is not limited to the above example.

  For example, as illustrated in FIG. 4, an npn bipolar transistor may be employed as the switching element 12. In this case, the base is connected to the output terminal of the operational amplifier 16, the emitter is the output terminal 14 side (ground side), and the collector is the overcurrent detection resistor 32 side (power supply side). The configuration of the power supply device excluding the switching element 12 and the overcurrent protection circuit 30 is the same as the configuration of the above embodiment (see FIG. 1).

  Further, as shown in FIG. 5, a pnp bipolar transistor may be employed as the switching element 12. In this case, the configuration of the power supply device (driver circuit) is partially different from the above embodiment. Specifically, the base of an npn-type bipolar transistor 24 is connected to the output terminal of the operational amplifier 16, the emitter of the bipolar transistor 24 is connected to the ground, and the collector is connected to the base of the switching element 12. The collector of the bipolar transistor 44 connected to the output terminal of the comparator 42 is connected to the connection point between the output terminal of the operational amplifier 16 and the base of the bipolar transistor 24. The collector of the switching element 12 is on the output terminal 14 side (ground side), and the emitter is on the overcurrent detection resistor 32 side (power supply side).

  In this configuration, the potential input to the non-inverting input terminal (+) when the power is on is higher than the potential input to the inverting input terminal (−) (the midpoint potential of the resistors 20 and 22). Then, the bipolar transistor 24 is turned on, and the switching element 12 is turned on. On the other hand, when the potential input to the non-inverting input terminal (+) becomes lower than the potential input to the inverting input terminal (−), the bipolar transistor 24 is turned off, and the switching element 12 is turned off. Further, when the output of the comparator 42 becomes a high signal, the bipolar transistor 44 is turned on, whereby the bipolar transistor 24 is turned off, and the switching element 12 is turned off.

  In addition, as shown in FIG. 6, a p-channel type MOS may be employed as the switching element 12. In FIG. 6, the configuration of the power supply device excluding the switching element 12 and the overcurrent protection circuit 30 is the same as that of FIG. 5, and the collector of the bipolar transistor 24 is connected to the gate. In this case, the drain of the switching element 12 is the output terminal 14 side (ground side), and the source is the overcurrent detection resistor 32 side (power supply side).

(Second Embodiment)
In the present embodiment, descriptions of parts common to the overcurrent protection circuit and the power supply device described in the above embodiment are omitted. In the first embodiment, the second trim resistor 38 is connected to the ground side of the first constant current source 36, and the second trim resistor 38 is laser-trimmed so that the manufacturing variation of the overcurrent detection resistor 32 (initial stage) is reduced. An example in which the offset) can be corrected is shown.

  On the other hand, in this embodiment, as shown in FIG. 7, the A / D converters 80 and 82, the microcomputer 84, and the memory 86 are further provided with respect to the structure of 1st Embodiment. On the other hand, the second trim resistor 38 and the bipolar transistor 44 are eliminated.

  The potential V1 of the voltage detection terminal (ground side terminal) of the overcurrent detection resistor 32 is input to the comparator 42 via the A / D converter 80. On the other hand, the potential Vref at the first connection point 40 is input to the microcomputer 84 via the A / D converter 82, and the input data is stored in the memory 86 by the microcomputer 84. Electric trimming is performed using data for correcting manufacturing variations. Then, the electrically trimmed data is input to the comparator 44 and compared with the data related to the potential V1. The memory 86 corresponds to storage means described in the claims, and the microcomputer corresponds to correction means.

  Such electrical trimming can also correct manufacturing variations in the overcurrent detection resistor 32.

  In this embodiment, an example in which the second trim resistor 38 is not provided is shown. However, a laser trim of the second trim resistor 38 and an electric trim by the microcomputer 84 and the memory 86 may be used in combination.

  Furthermore, the electric trim shown in the present embodiment can also be applied to various modifications shown in the first embodiment.

(Third embodiment)
In the present embodiment, descriptions of parts common to the overcurrent protection circuit and the power supply device described in the above embodiment are omitted. In each of the above-described embodiments, the reference resistor 34 is composed of only a resistor having no temperature characteristic.

  On the other hand, in this embodiment, as shown in FIG. 8, the reference resistor 34 has a configuration in which a resistor 34a having no temperature characteristic and a resistor 34b having a positive temperature characteristic are connected in series. Yes. A resistor formed using CrSi or polySi can be used as the resistor 34a, and a diffused resistor can be used as the resistor 34b. According to this, since the reference resistor 34 can have a positive temperature characteristic with a small inclination, the configuration of the second constant current source 50 can be simplified.

(Fourth embodiment)
In the present embodiment, the description of the parts common to the overcurrent protection circuit shown in the above embodiment is omitted. In each of the above embodiments, an example of the power supply device that supplies power to the microcomputer as the load 10 and the overcurrent protection circuit 30 corresponding to the power supply device has been described.

  On the other hand, the present embodiment is characterized by a low-side load driving device that controls driving of the load 10 (current flowing through the load 10) and an overcurrent protection circuit 30 corresponding to the load driving device. To do. An example is shown in FIG. FIG. 9 basically follows the configuration of the first embodiment (see FIG. 1), and a description will be given centering on differences from FIG.

  First, the parts of the comparator 42 and the bipolar transistor 44 in the load driving circuit including the switching element 12 and the overcurrent protection circuit 30 will be described.

  As shown in FIG. 9, the load 10 and the switching element 12 are connected in series between the power supply and the ground, with the load 10 (inductor) being the power supply side (high potential side) and the switching element 12 being the ground side (low potential side). Is done.

  As the switching element 12, an n-channel type MOS is employed as in the first embodiment. An overcurrent detection resistor 32 is connected to the source (ground side terminal) of the switching element 12, and one terminal of the overcurrent detection resistor 32 is connected to the ground. A connection point between the source of the switching element 12 and the overcurrent detection resistor 32 is a voltage detection terminal of the overcurrent detection resistor 32. The potential V1 of the voltage detection terminal is input to the non-inverting input terminal (+) of the comparator 42, and the potential Vref of the first connection point 40 is input to the inverting input terminal (−).

  The output terminal of the comparator 42 is connected to the base of the npn-type bipolar transistor 44, and the emitter of the bipolar transistor 44 is connected to the ground and the collector is connected to the gate of the switching element 12. A driver circuit 26 is connected to a connection point between the collector and the gate.

  Therefore, when an overcurrent flows through the overcurrent detection resistor 32, the potential V1 rises compared to when no overcurrent flows, and V1> Vref, and a high signal is output from the comparator 42. As a result, the bipolar transistor 44 is turned on, the gate of the switching element 12 becomes the ground potential, and the switching element 12 is turned off. Thereby, supply of electric power (current) to the load 10 is interrupted. Note that during normal times when no overcurrent flows, V1 <Vref, and the comparator 42 outputs a low signal. Thereby, the bipolar transistor 44 is turned off, and the switching element 12 is controlled to be turned on / off based on the drive signal from the driver circuit 26.

  Next, the reference resistor 34, the first constant current source 36, and the second trim resistor 38 will be described.

  One end of the reference resistor 34 is connected to the ground. That is, the ground side terminal of the reference resistor 34 has the same potential (ground potential) as the ground side terminal of the overcurrent detection resistor 32.

  The first constant current source 36 includes a sixth constant current source 36a that supplies a sixth constant current I6 that does not have temperature characteristics. The seventh transistor 36b is arranged on the power supply side and connected in series to the sixth constant current source 36a, and the eighth transistor 36c has a ground-side terminal connected to the first connection point 40. A fourth current mirror circuit is included.

  The power supply side terminal of the sixth constant current source 36a is connected to the collector of a pnp bipolar transistor constituting the seventh transistor 36b, and the emitter of the seventh transistor 36b is connected to the power supply. The base of the seventh transistor 36b is connected to the base of a pnp-type bipolar transistor constituting the eighth transistor 36c, and the base is connected to the collector of the seventh transistor 36b. Therefore, the current flowing through the eighth transistor 36c, that is, the first constant current I1 supplied from the first constant current source 36 to the first connection point 40 is I1 = I6.

  The fourth trim resistor 46 is connected to the emitter of the eighth transistor 36c, and the power supply side terminal of the fourth trim resistor 46 is connected to the power source.

  Thus, the first constant current source 36 is connected to the power supply side terminal of the reference resistor 34.

  Of the second constant current source 50, a third constant current source 52, a fourth constant current source 54, a first current mirror circuit 56, a fifth constant current source 58, a third transistor 60a, a current path 62, and a diode 62a are formed. Since the structure of the part made is the same as 1st Embodiment, it abbreviate | omits description.

  The third transistor 60a and the fourth transistor 60b constitute a second current mirror circuit 60. In the present embodiment, the ground side terminal of the fourth transistor 60b is connected to the ground, and the fifth transistor 66a is connected to the power supply side terminal. The fifth transistor 66a is a pnp type bipolar transistor, the collector of which is connected to the collector constituting the fourth transistor 60b, and the emitter of which is connected to the power supply.

  The fifth transistor 66a and the plurality of sixth transistors 66b having the ground-side terminal connected to the first connection point 40 and arranged in parallel to each other constitute a plurality of third current mirror circuits 66. . The sixth transistor 66b is also a pnp bipolar transistor, and has a collector connected to the first connection point 40 and a third trim resistor 68 connected to the emitter. The power supply side terminal of the third trim resistor 46 is connected to the power supply.

  In the second constant current source 50 configured as described above, the current Ic is Ic = (I5 + Ib) as in the first embodiment. As shown in the first embodiment, the current Ib is Ib = (I4-Ia) and has a positive temperature characteristic. Further, the current Id flowing through the fourth transistor 60b constituting the second current mirror circuit 60 is Id = Ic.

  As described above, the fifth transistor 66a constituting the third current mirror circuit 66 is connected in series to the fourth transistor 60b, and the current Id also flows through the fifth transistor 66a. Therefore, the current If flowing through each of the sixth transistors 66b configuring the third current mirror circuit 66 is If = Id. Thus, the second constant current I2 supplied from the second constant current source 50 to the first connection point 40 is I2 = If × the number of sixth transistors 66b (the number of third current mirror circuits 66). In the present embodiment, since there are two sixth transistors 66b, I2 = 2 × If.

  As described above, the overcurrent protection circuit 30 according to this embodiment applied to the low-side load driving device can also achieve the same effects as the overcurrent protection circuit 30 shown in the first embodiment.

  Specifically, also in the present embodiment, the current Ib flowing through the current path 62 constituting the second constant current source 50 substantially has a negative temperature characteristic from the fourth constant current I4 that does not have a temperature characteristic. The third constant current I3 (= Ia) is subtracted. Thus, the current Ib has a positive temperature characteristic. In the second constant current source 50, using the current Ib having the positive temperature characteristic, the temperature characteristic of the potential Vref at the first connection point 40 is equal to the temperature characteristic of the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. A second constant current I2 that is equal is formed.

  The third constant current source 52 that supplies the third constant current I3 having negative temperature characteristics is formed on the same semiconductor substrate as the overcurrent detection resistor 32 having positive temperature characteristics. For this reason, the temperature of the overcurrent detection resistor 32 and the temperature of the third constant current source 52 are substantially the same.

  Therefore, the potential Vref at the first connection point 40 to be compared with the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32 is changed according to the temperature as in the case of the potential V1, and the influence of the temperature characteristics of the overcurrent detection resistor 32 is affected. Can be canceled.

  At that time, the positive temperature characteristic (slope) of the second constant current I2 can be set to a desired value by the number of the sixth transistors 66b, that is, the third current mirror circuits 66.

  In the present embodiment, the third trim resistors 68 are connected to the emitters of the sixth transistors 66 b constituting the third current mirror circuit 66. According to this, by changing the resistance value of the third trim resistor 68 by laser trim, the temperature characteristic of the potential Vref at the first connection point 40 is changed to the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. It can be adjusted to the temperature characteristics. That is, the influence of the temperature characteristic of the overcurrent detection resistor 32 can be canceled with higher accuracy.

  In the present embodiment, the fourth trim resistor 46 is connected to the power supply side of the eighth transistor 36 c constituting the first constant current source 36. According to this, by changing the resistance value of the fourth trim resistor 46 by laser trim, the potential Vref at the first connection point 40 is detected at the potential V1 of the voltage detection terminal of the overcurrent detection resistor 32. It is possible to correct the manufacturing variation of the resistor 32 (resistance value variation caused by the manufacturing). The manufacturing variation is, in other words, an intercept (initial offset) with respect to the inclination.

(Modification)
In addition to the above embodiment, although not shown, a plurality of eighth transistors 36c may be arranged in parallel between the power source and the first connection point 40, and a plurality of fourth current mirror circuits may be configured. Also by this, the manufacturing variation of the overcurrent detection resistor can be corrected by the number of the eighth transistors 36c.

  In the embodiment described above, the fourth trim resistor 46 is provided in series with the eighth transistor 36c. However, the fourth trim resistor 46 may be connected to at least one of the emitter of the seventh transistor 36c and the emitter of the eighth transistor 36c constituting the current mirror circuit.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In this embodiment, the example in which the switching element 12, the driver circuit of the switching element 12, and the overcurrent protection circuit 30 are formed on the same semiconductor substrate (one chip) is shown. However, the overcurrent detection resistor 32 having a positive temperature characteristic and the third constant current source 52 that supplies the third constant current I3 having a negative temperature characteristic may be formed on at least the same substrate.

DESCRIPTION OF SYMBOLS 10 ... Load 12 ... Switching element 30 ... Overcurrent protection circuit 32 ... Overcurrent detection resistor 34 ... Reference resistor 36 ... First constant current source 40 ... First connection point 42 ... Comparator 50 ... Second constant current source 52 ... Third constant current source 54 ... Fourth constant current source 56 ... First current mirror circuit 58 ... Fifth constant current source 60 ... second current mirror circuit 62 ... current path I1 ... first constant current I2 ... second constant current I3 ... third constant current I4 ... fourth constant current

Claims (14)

An overcurrent detection resistor having a positive temperature characteristic and connected in series with a switching element that controls supply of power to a load between a power supply and a ground;
With respect to the overcurrent detection resistor, a reference resistor arranged such that either the power supply side terminals or the ground side terminals have the same potential;
A first constant current source connected to a terminal opposite to a terminal having the same potential as the overcurrent detection resistor in the reference resistor, and supplying a first constant current having no temperature characteristic to the reference resistor;
The voltage signal of the terminal opposite to the terminal having the same potential as the reference resistor in the overcurrent detection resistor is input to one input terminal, and the reference resistor and the first constant current source are connected to the other input terminal. A comparator to which the voltage signal of the connected first connection point is input,
An overcurrent protection circuit for controlling on / off of the switching element so as to cut off power supplied to the load when an overcurrent flows through the overcurrent detection resistor based on an output of the comparator;
In the first connection point, the temperature characteristic of the potential of the first connection point is equal to the temperature characteristic of the potential of the terminal opposite to the terminal having the same potential as the reference resistance in the overcurrent detection resistor. A second constant current source for supplying a second constant current having a positive temperature characteristic to the first connection point is connected;
The second constant current source is
A third constant current source for supplying a third constant current having a negative temperature characteristic;
A fourth constant current source for supplying a fourth constant current having no temperature characteristic;
A first current mirror circuit configured by a first transistor connected in series to the third constant current source and a second transistor connected in series to the fourth constant current source;
A current path connected to a connection point between the fourth constant current source and the second transistor and supplying the second constant current to the first connection point;
The overcurrent protection circuit, wherein the third constant current source is formed on the same substrate as the overcurrent detection resistor. The overcurrent detection resistor is disposed on the power supply side with respect to the switching element,
The power supply side terminal of the reference resistor is connected to the power supply side terminal of the overcurrent detection resistor,
The first constant current source is connected to a ground side terminal of the reference resistor,
The voltage signal of the ground connection terminal of the overcurrent detection resistor is input to the inverting input terminal of the comparator, and the voltage signal of the first connection point is input to the non-inverting input terminal. The overcurrent protection circuit according to Item 1. The second constant current source is
A fifth constant current source for supplying a fifth constant current having no temperature characteristic;
A plurality of third transistors connected in series to the fifth constant current source, and a plurality of fourth transistors whose terminals on the power supply side are connected to the first connection point and arranged in parallel with each other. A second current mirror circuit,
The current path electrically connects a connection point between a fourth constant current source and the second transistor and a connection point between the fifth constant current source and the third transistor. Item 3. The overcurrent protection circuit according to Item 2.   4. The overcurrent protection circuit according to claim 3, wherein a first trim resistor is connected in series to each of the fourth transistors.   5. The overcurrent protection according to claim 2, wherein a second trim resistor is connected in series to the first constant current source between the first connection point and the ground. circuit.   The overcurrent protection circuit according to claim 5, wherein a plurality of the first constant current sources arranged in parallel with each other are connected to the first connection point. The overcurrent detection resistor is disposed on the ground side with respect to the switching element,
The ground side terminal of the overcurrent detection resistor and the ground side terminal of the reference resistor have the same potential,
The first constant current source is connected to a power supply side terminal of the reference resistor,
The voltage signal of the power supply side terminal of the overcurrent detection resistor is input to the non-inverting input terminal of the comparator, and the voltage signal of the first connection point is input to the inverting input terminal. The overcurrent protection circuit according to Item 1. The second constant current source is
A fifth constant current source for supplying a fifth constant current having no temperature characteristic;
A second current mirror circuit composed of a third transistor and a fourth transistor connected in series to the fifth constant current source;
A fifth transistor disposed on the power supply side with respect to the fourth transistor and connected in series between the power supply and the ground, and a plurality of terminals on the ground side connected to the first connection point and disposed in parallel with each other A plurality of third current mirror circuits configured by the sixth transistor,
The current path electrically connects a connection point between a fourth constant current source and the second transistor and a connection point between the fifth constant current source and the third transistor. Item 8. The overcurrent protection circuit according to Item 7.   9. The overcurrent protection circuit according to claim 8, wherein a third trim resistor is connected in series to each fifth transistor. The first constant current source is:
A sixth constant current source for supplying a sixth constant current having no temperature characteristic;
A fourth current mirror comprising: a seventh transistor arranged in series with respect to the sixth constant current source and connected in series; and an eighth transistor having a ground-side terminal connected to the first connection point. The overcurrent protection circuit according to claim 7, further comprising a circuit.   11. The overcurrent according to claim 10, wherein a fourth trim resistor is connected in series to at least one of the seventh transistor and the eighth transistor between the first connection point and a power source. Protection circuit. A plurality of the fourth current mirror circuits are configured by arranging a plurality of the eighth transistors in parallel with each other,
The overcurrent protection circuit according to claim 11, wherein the fourth trim resistor is connected in series to each eighth transistor. Storage means for storing data for correcting manufacturing variations of the overcurrent detection resistor;
The correction means which correct | amends the voltage signal of the said 1st connection point with the data memorize | stored in the said memory, and makes it input into the input terminal of the said comparator is provided. The overcurrent protection circuit described.   14. The overcurrent protection according to claim 1, wherein the reference resistor is formed by connecting a resistor having no temperature characteristic and a resistor having a positive temperature characteristic to each other in series. circuit.

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