JP4530878B2 - Voltage comparator, overcurrent detection circuit using the same, and semiconductor device - Google Patents

Description

  The present invention relates to a voltage comparator, and more particularly to an inspection technique thereof.

  In a regulator circuit that stabilizes a voltage, a power MOSFET (Metal Oxide Field Effect Transistor), an IGBT (insulated gate bipolar transistor), a bipolar power transistor, or the like is used as an output transistor. These transistors are designed to have a sufficient margin with respect to the current value flowing during normal operation as the maximum allowable current.

  However, even when designing with a sufficient design margin in this way, when the output load circuit is short-circuited, a large overcurrent exceeding the maximum allowable current flows through the transistor, affecting its reliability. There was a problem. In some cases, it is desired to limit the current to protect the load circuit connected to the transistor even if it is less than the maximum allowable current of the transistor.

  Therefore, conventionally, in order to protect the power transistor from overcurrent or limit the current flowing in the load circuit, an overcurrent protection circuit, a current limit circuit, and the like are provided to protect the circuit (Patent Document 1). Patent Document 2).

  In a circuit that performs such overcurrent detection (hereinafter referred to as an overcurrent detection circuit), as disclosed in Patent Document 1, an operational amplifier is used as a voltage comparator to convert a current to be detected into a voltage, An overcurrent condition is detected by comparing the voltage with a predetermined threshold voltage.

  Here, an operational amplifier used as a voltage comparator may have an offset between the non-inverting input terminal and the inverting input terminal. This offset causes the voltage comparator to compare the detection voltage with the threshold voltage shifted by the offset instead of the predetermined threshold voltage, so that the threshold current for overcurrent detection is shifted by the offset. As a result, the reliability of the circuit may be affected.

To solve this problem, consider the case where the offset of the operational amplifier is measured in advance. FIG. 4 shows an example of a circuit diagram for measuring an offset of a voltage comparator constituted by an operational amplifier.
The voltage comparator 200 includes an operational amplifier 10, a reference voltage source 12, and resistors R1 and R2. The inspection voltage Vin applied to the input terminal 102 is divided by the resistors R1 and R2 and input to the non-inverting input terminal of the operational amplifier 10. The reference voltage Vref output from the reference voltage source 12 is applied to the non-inverting input terminal of the operational amplifier 10. In an ideal state where there is no offset in the operational amplifier 10, the voltage comparator 200 sets the threshold voltage to Vth = Vref × (R1 + R2) / R2, and sets the low level when Vin> Vth and the high level when Vin <Vth. The level is output from the output terminal 104.

Japanese Patent Laid-Open No. 5-315852 JP 2002-304225 A

The threshold voltage of the voltage comparator 200 actually deviates from the above ideal state due to the offset of the operational amplifier 10 or the like. In order to measure the actual threshold voltage Vth of the voltage comparator 200, a first voltmeter 300 and a voltage source 302 are connected to the input terminal 102 of the voltage comparator 200. A second voltmeter 304 is connected to the output terminal 104.
The voltage source 302 sweeps the inspection voltage Vin, the first voltmeter 300 measures the inspection voltage Vin, and the second voltmeter 304 measures the output voltage Vout. When the inspection voltage Vin is swept, the output voltage Vout is switched from a high level to a low level when a certain value is reached. The value of the inspection voltage Vin at this time becomes the threshold voltage of the voltage comparator 200.

  However, when the threshold voltage of the voltage comparator 200 is measured by the circuit of FIG. 4, it is necessary to sweep the inspection voltage Vin, which causes a problem that it takes time for the inspection. In addition, there is a problem that the first voltmeter 300, the voltage source 302, and the second voltmeter 304 are necessary as measurement devices, and the device becomes complicated. Further, when the voltage comparator 200 is integrated in an LSI (Large Scale Integration), the input terminal 102 and the output terminal 104 are formed as test pads in order to connect the voltage source 302 and the second voltmeter 304. There is also a problem that the circuit area increases.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a voltage comparator capable of easily inspecting a threshold voltage and adjusting the threshold voltage as necessary, and The overcurrent detection circuit used is provided.

  One embodiment of the present invention relates to a voltage comparator. This voltage comparator is a voltage comparator that compares a test voltage applied to an input terminal with a predetermined threshold voltage, a reference voltage source that generates a predetermined reference voltage, and a test voltage applied to an inverting input terminal. Applied to the operational amplifier in which the reference voltage is applied to the non-inverting input terminal, and provided between the output terminal and the input terminal of the operational amplifier, and is turned on in the inspection mode in which the threshold voltage of the voltage comparator is inspected. A switch that is turned off in a normal mode for comparing the voltage and the threshold voltage.

  According to this aspect, in the normal mode, the feedback path to the output terminal and the input terminal of the operational amplifier is cut off by turning off the switch, and the operational amplifier operates as a voltage comparator. In the inspection mode, when the switch is turned on, the output terminal and the non-inverting input terminal of the operational amplifier are connected to operate as a feedback amplifier. The threshold voltage of the voltage comparator can be measured by turning on the switch while stopping the application of the inspection voltage to the input terminal and measuring the voltage appearing at the output terminal of the operational amplifier.

  The voltage comparator may further include a switch control unit that controls an on / off state of the switch.

The voltage comparator may further include a resistor group that divides the test voltage applied to the input terminal and outputs the divided voltage to the inverting input terminal of the operational amplifier.
When a resistance group that divides the test voltage is provided, the threshold voltage should be measured even when the threshold voltage of the voltage comparator is shifted due to the offset of the operational amplifier or the resistance value of the resistance group. Can do.

  More preferably, any of the resistors included in the resistor group is formed so as to be capable of being trimmed. When the threshold voltage is measured in the inspection mode by forming the resistor so that it can be trimmed, if the deviation is from the desired value, the voltage comparison having the desired threshold voltage is performed by trimming the resistor. Can be obtained.

Instead of the switch, the portion may be directly connected by wiring, and the switch may be turned on by the wiring, and the switch may be turned off by cutting the wiring.
According to this aspect, the feedback amplifier and the voltage comparator can be switched by using the wiring instead of the switch and cutting the wiring, and can be used as the voltage comparator after measuring the threshold voltage. . The “cutting the wiring” includes not only physically cutting the wiring but also removing the 0Ω resistor or removing the jumper line.

  Another aspect of the present invention is an overcurrent detection circuit. This overcurrent detection circuit includes a current-voltage conversion unit that converts a current to be detected into a voltage, and the voltage comparator described above to which a voltage output from the current-voltage conversion unit is input as a test voltage. When the voltage output from the voltage converter exceeds the threshold voltage of the voltage comparator, the overcurrent state is determined.

  According to this aspect, since the threshold voltage of the voltage comparator can be measured in the inspection mode, the detection threshold current in the overcurrent state can be measured and the detection threshold current can be corrected. .

Another embodiment of the present invention is a semiconductor device. This semiconductor device includes the above-described overcurrent detection circuit, and operates so as to limit the current to be detected when the overcurrent detection circuit detects an overcurrent state.
According to this aspect, since the detection threshold current in the overcurrent state can be set accurately, heat generation of the semiconductor device can be suitably prevented, and the reliability of the product can be improved.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the voltage comparator of the present invention, the threshold voltage can be easily inspected, and the threshold voltage can be corrected as necessary. Further, the overcurrent detection circuit according to the present invention can correct the threshold current. Furthermore, according to the semiconductor device of the present invention, the reliability can be improved.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a voltage comparator 100 according to the first embodiment of the present invention. The voltage comparator 100 according to the present embodiment is integrated in an LSI, and compares the inspection voltage Vin applied to the input terminal 102 with a predetermined threshold voltage Vth. The output terminal 104 outputs a low level output voltage Vout when Vin> Vth and a high level output voltage when Vin <Vth.

The voltage comparator 100 includes an operational amplifier 10, a reference voltage source 12, resistors R1 and R2, a switch SW1, and a switch control unit 14.
The reference voltage source 12 generates a predetermined reference voltage Vref. In the operational amplifier 10, a reference voltage source 12 is connected to a non-inverting input terminal, and a reference voltage Vref is applied.
Resistors R1 and R2 are connected in series between the input terminal 102 and the ground potential, and the connection point of the resistors R1 and R2 is connected to the inverting input terminal of the operational amplifier 10. The inspection voltage Vin is divided by the resistors R1 and R2, and the voltage Vx = Vin × R2 / (R1 + R2) is applied to the inverting input terminal of the operational amplifier 10. The output terminal of the operational amplifier 10 is the output terminal 104 of the voltage comparator 100.

The switch SW1 is provided between the output terminal of the operational amplifier 10, that is, the output terminal 104 and the input terminal 102. The switch SW1 is turned on in the test mode for testing the threshold voltage Vth of the voltage comparator 100, and is turned off in the normal mode for comparing the test voltage Vin with the threshold voltage Vth. The on / off state of the switch SW1 is switched by a control signal CNT output from the switch control unit 14. The switch SW1 can be constituted by an analog switch using, for example, a MOSFET.
The switch control unit 14 determines the normal mode and the inspection mode, and outputs a control signal CNT so that the switch SW1 is turned on in the inspection mode and the switch SW1 is turned off in the normal mode.

In the normal mode in which the voltage comparator 100 performs voltage comparison, the switch SW1 is turned off by the control signal CNT. At this time, the feedback path to the output terminal 104 and the input terminal 102 of the operational amplifier 10 is cut off, and the operational amplifier 10 operates as a voltage comparator.
The output voltage Vout of the operational amplifier 10 is low level when Vx> Vref, and high level when Vx <Vref. Now, since Vx = Vin × R2 / (R1 + R2) holds, the voltage comparator 100 operates as a voltage comparator in which the threshold voltage Vth is given by Vth = Vref × (R1 + R2) / R2, where Vin> A low level is output when Vth, and a high level is output when Vin <Vth.

  The operation in the inspection mode for measuring the threshold voltage Vth of the voltage comparator 100 configured as described above will be described. FIG. 2 is a circuit diagram for measuring the threshold voltage of the voltage comparator 100 according to the present embodiment. In the subsequent drawings, the same or equivalent components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In order to measure the threshold voltage Vth, a voltmeter 306 is connected to the input terminal 102.

In the inspection mode, the switch SW1 is turned on by the control signal CNT. By turning on the switch SW1, the output terminal and the inverting input terminal of the operational amplifier 10 are connected via the resistor R1, and operate as a feedback amplifier.
If the input impedance of the operational amplifier 10 is sufficiently high and the on-resistance of the switch SW1 is sufficiently lower than the resistance values of the resistors R1 and R2, almost no current flows through the switch SW1, so that the voltage at the switch SW1 You can ignore the descent. Therefore, when the switch SW1 is turned on in a state where the application of the inspection voltage Vin to the input terminal 102 is stopped, the output voltage Vout appears at the input terminal 102.

In an ideal operational amplifier, the voltages of the inverting input terminal and the non-inverting input terminal are equal in a balanced state. However, in an actual operational amplifier, these voltages are shifted due to an offset. When the voltage of the inverting input terminal at this time is Vref ′, the voltages of the input terminal 102 and the output terminal 104 are Vin = Vout = Vref ′ × (R1 + R2) / R2. Vin and Vout at this time become the threshold voltage Vth of the voltage comparator 100.
Therefore, when the output voltage Vout is measured by the voltmeter 306 connected to the input terminal 102 and the value is Vout1, the threshold voltage Vth of the voltage comparator 100 is Vout1.

  As described above, according to the voltage comparator 100 according to the present embodiment, a switch is provided between the output terminal 104 of the operational amplifier 10 and the input terminal 102 to which the inspection voltage Vin is applied, and the switch is turned on in the inspection mode. By doing so, the threshold voltage of the voltage comparator 100 can be measured.

  In this case, compared with the measurement method shown in FIG. 4, it is not necessary to apply and sweep the inspection voltage Vin, so that the inspection time can be shortened. In addition, since the voltage measurement only needs to be performed for one of the voltages appearing at the input terminal 102 or the output terminal 104, the inspection apparatus can be simplified. Furthermore, voltage measurement may be performed only for either the input terminal 102 or the output terminal 104, and only one of the test pads may be provided, so that the circuit area can be reduced.

  In FIG. 2, the case where the voltmeter 306 is connected to the input terminal 102 has been described. However, when the voltage drop of the switch SW1 can be ignored, the voltmeter 306 may be connected to the output terminal 104 to measure the voltage.

Further, the resistors R1 and R2 that divide the inspection voltage Vin may be omitted, the resistor R2 may be open, and the resistor R1 may be short-circuited. At this time, the threshold voltage Vth of the voltage comparator 100 is equal to the reference voltage Vref generated by the reference voltage source 12 in an ideal state.
Even in this case, the threshold voltage of the voltage comparator 100 can be measured by measuring the voltage appearing at the input terminal 102 or the output terminal 104 with the switch SW1 turned on.

(Second Embodiment)
The second embodiment of the present invention is an overcurrent detection circuit.
FIG. 3 is a circuit diagram showing a configuration of the overcurrent detection circuit according to the present embodiment. The overcurrent detection circuit 500 includes a current / voltage converter 400 and a voltage comparator 100.

  The current-voltage conversion unit 400 converts a current to be detected (hereinafter referred to as a detection current) Idet into a detection voltage Vdet and outputs the detection voltage Vdet to the input terminal 102 of the voltage comparator 100. The current-voltage conversion unit 400 includes a first transistor M1, a second transistor M2, and a resistor R3. The first transistor M1 is a P-type MOSFET, and is provided in a path through which the detection current Idet flows. The second transistor M2 is a P-type MOSFET like the first transistor M1, and the gate terminal and source terminal of the first transistor M1 are connected in common. The second transistor M2 generates a current Im2 = S1 × Idet that is proportional to the detection current Idet flowing through the first transistor M1. Here, S1 is a size ratio of the first transistor M1 and the second transistor M2.

  The resistor R3 is provided between the drain terminal of the second transistor M2 and the ground potential. A current Im2 flowing through the second transistor M2 flows through the resistor R3, and a voltage drop of R3 × Im2 = R3 × S1 × Idet occurs. The current-voltage conversion unit 400 outputs a voltage drop generated in the resistor R3 as the detection voltage Vdet.

The operation of the overcurrent detection circuit 500 configured as described above will be described.
In the inspection mode, as described in the first embodiment, the threshold voltage Vth can be measured by turning on the switch SW1.

The resistor R2 of the voltage comparator 100 according to the present embodiment is formed so as to be capable of trimming. When the threshold voltage Vth measured in the inspection mode deviates from a predetermined value, the threshold voltage Vth can be adjusted by trimming the resistor R2.
Instead of the resistor R2, the resistor R1 may be formed so as to be capable of trimming, or both may be formed so as to be capable of trimming.

In the normal mode in which the overcurrent state is detected, the switch SW1 is turned off.
The voltage comparator 100 outputs a low level when Vdet> Vth, and outputs a high level when Vdet <Vth. When the detection current Idet increases, the detection voltage Vdet increases, and when it exceeds the threshold current, the output of the voltage comparator 100 changes from a high level to a low level, and an overcurrent state can be detected. .

According to the overcurrent detection circuit 500 according to the present embodiment, the threshold voltage Vth of the voltage comparator 200 can be easily measured, and the threshold current Ith for overcurrent detection is Ith = Vth / (R3 × S1 ).
Further, by trimming the resistors R1 and R2 based on the measured threshold voltages, the threshold voltage Vth, that is, the threshold current Ith can be adjusted, so that an accurate overcurrent state is detected. be able to. Trimming may be performed in a fuse form or may be performed in a circuit using a nonvolatile memory.
In a semiconductor device using this overcurrent detection circuit 500, an accurate overcurrent state can be detected, so that heat generation can be reduced and the reliability of the product can be improved.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the case where the switch SW1 is a MOSFET has been described. However, the present invention is not limited to this, and a bipolar transistor or other switch element may be used. When the threshold voltage is measured only at the time of LSI inspection, the switch SW1 may be formed by an aluminum wiring that can be cut off. In this case, at the time of LSI inspection, the threshold voltage Vth is measured as described above in a state where the output terminal 104 and the input terminal 102 of the voltage comparator 100 are connected by the aluminum wiring, and the aluminum wiring is cut after the measurement. By doing so, the switch SW1 can be turned off, and it can be operated as a highly accurate voltage comparator.

  In the embodiment, the on / off state of the switch SW1 is controlled by the switch control unit 14, but is not limited thereto. For example, when the switch SW1 is a MOSFET, a pad may be provided on the gate terminal so that a voltage can be applied from the outside, and the MOSFET may be turned on by applying a voltage from the outside between the gate and source in the inspection mode.

  In the embodiment, the transistor used in the current-voltage conversion unit 400 and the like has been described only for the MOSFET, but another type of transistor such as a bipolar transistor may be used. These selections may be determined according to design specifications required for the power supply device, a semiconductor manufacturing process to be used, and the like.

  In the embodiment, all the elements constituting the voltage comparator and the overcurrent detection circuit may be integrated, or a part thereof may be constituted by discrete components. Which part is integrated may be determined based on the semiconductor manufacturing process to be used, cost, occupied area, and the like.

It is a circuit diagram which shows the structure of the voltage comparator which concerns on 1st Embodiment. FIG. 2 is a circuit diagram for measuring a threshold voltage of the voltage comparator of FIG. 1. It is a circuit diagram which shows the structure of the overcurrent detection circuit which concerns on 2nd Embodiment. It is a circuit diagram for measuring the offset of the voltage comparator comprised with an operational amplifier.

Explanation of symbols

  10 operational amplifier, 12 reference voltage source, 14 switch control unit, 100 voltage comparator, 200 voltage comparator, SW1 switch, 102 input terminal, 104 output terminal, 302 voltage source, 400 current voltage conversion unit, 500 overcurrent detection circuit R1 resistance, R2 resistance.

Claims (7)

A voltage comparator for comparing a test voltage applied to an input terminal with a predetermined threshold voltage,
A reference voltage source for generating a predetermined reference voltage;
An operational amplifier in which the test voltage is applied to an inverting input terminal and the reference voltage is applied to a non-inverting input terminal;
Provided between the output terminal and the input terminal of the operational amplifier and turned on in a test mode for testing the threshold voltage of the voltage comparator, and turned off in a normal mode for comparing the test voltage and the threshold voltage A switch to
A voltage comparator comprising:   The voltage comparator according to claim 1, further comprising a switch control unit that controls an on / off state of the switch.   The voltage comparator according to claim 1, further comprising a resistor group that divides a test voltage applied to the input terminal and outputs the divided voltage to an inverting input terminal of the operational amplifier.   The voltage comparator according to claim 3, wherein any one of the resistors included in the resistor group is formed to be capable of trimming.   2. The switch according to claim 1, wherein the switch is directly connected by a wiring instead of the switch, the switch is turned on by the wiring, and the switch is turned off by cutting the wiring. Voltage comparator. A current-voltage converter that converts the current to be detected into a voltage; and
A voltage comparator according to any one of claims 1 to 5, wherein a voltage output from the current-voltage converter is input as a test voltage;
An overcurrent detection circuit that determines an overcurrent state when a voltage output from the current-voltage converter exceeds a threshold voltage of the voltage comparator.   A semiconductor device comprising the overcurrent detection circuit according to claim 6, wherein when the overcurrent detection circuit detects an overcurrent state, the semiconductor device operates to limit a current to be detected.

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