JP6571031B2 - Open / short inspection circuit and load driving device - Google Patents

Description

  The present invention relates to an open / short inspection circuit for inspecting an open state and a short state of a resistor, and a load driving device in which a resistor for current detection or the like is provided in a path of a current flowing by driving a load.

  As a method for inspecting the connection state of a circuit, a method is generally employed in which a constant current is supplied from a constant current source to the circuit and a voltage generated by the current is measured. For example, in the integrated circuit inspection method described in the following patent document, a constant current source is connected to an integrated circuit mounted on a circuit board to supply a constant current, and a voltage generated by the current is measured and measured. By comparing the result with a predetermined reference value, the soundness of the circuit including the connection state is inspected.

JP 2007-155640 A

  For example, when driving a load with a relatively large current, such as when driving a coil of a magnetically balanced current sensor, a shunt resistor having a small resistance value is used as a resistor for detecting the current flowing through the load. When inspecting an open state and a short state with respect to a resistor having a small resistance value, it is difficult to accurately perform each inspection because the voltage generated in the resistance differs greatly between the open state and the short state in the above-described conventional method. In particular, in the inspection of the short state, since the difference between the normal resistance value and the abnormal resistance value in the short state is small, there is a problem that the difference in the voltage generated in the resistance is also small and it is difficult to improve the inspection accuracy. There may be a method of providing dedicated test circuits for the open state test and the short state test, but this has the disadvantage of increasing the circuit scale.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an open / short inspection circuit capable of accurately inspecting an open state and a short state of a resistor with a simple configuration, and by driving a load. An object of the present invention is to provide a load driving device capable of accurately detecting an open state and a short state of a resistor provided in a path of a flowing current with a simple configuration.

  A first aspect of the present invention relates to an open / short inspection circuit that inspects an open state and a short state of a resistor. The open / short inspection circuit includes a current source that outputs current flowing in one direction to the resistor, an amplifier that amplifies a voltage generated in the resistor, and outputs a voltage obtained by adding a reference voltage to the amplification result; A first comparator for comparing the output voltage of the amplifier circuit with a first threshold voltage set as the determination condition for the open state; the output voltage of the amplifier circuit; and the determination condition for the short state Based on the second comparator for comparing the second threshold voltage, the output signal of the first comparator and the output signal of the second comparator, the presence or absence of the open state is determined in the first inspection mode; The inspection mode includes a determination circuit that determines the presence or absence of the short state. The amplifier circuit inverts the polarity of the gain between the first inspection mode and the second inspection mode. The reference voltage is a voltage between the first threshold voltage and the second threshold voltage.

  According to this configuration, independent comparators are used for the determination of the open state and the determination of the short state, and these two determinations are performed individually in independent inspection modes. Therefore, it is possible to set conditions suitable for each determination, and it is easy to improve the determination accuracy.

  Further, according to this configuration, the current source, the amplifier circuit, and the determination circuit are used in common in the first inspection mode and the second inspection mode. Therefore, the circuit configuration is simplified as compared with the case where dedicated test circuits are provided for the determination of the open state and the determination of the short state, respectively.

  Further, according to this configuration, while the current flows in one direction from the current source to the resistor, the gain polarity of the amplifier circuit is reversed between the first inspection mode and the second inspection mode. . Therefore, in one of the two inspection modes, as the resistance value of the resistor increases, the output voltage of the amplifier circuit becomes lower than the reference voltage and does not become higher than the reference voltage. In the other inspection mode, as the resistance value of the resistor increases, the output voltage of the amplifier circuit becomes higher than the reference voltage and does not become lower than the reference voltage. Since this reference voltage is a voltage between the first threshold voltage and the second threshold voltage, in the first inspection mode in which the presence or absence of the open state is determined by the output signal of the first comparator. Regardless of the output voltage of the amplifier circuit, the output signal of the second comparator is always a constant value. In the second inspection mode in which the presence or absence of the short-circuit state is determined based on the output signal of the second comparator, the output signal of the first comparator is always a constant value regardless of the output voltage of the amplifier circuit. That is, in each inspection mode, the output signal of one of the two comparators (first comparator and second comparator) is always a constant value. Therefore, the determination circuit can obtain the determination results of the two inspection modes with a simple circuit configuration based on the output signals of the two comparators.

  Preferably, the current source outputs a first constant current to the resistor in the first inspection mode, and outputs a second constant current larger than the first constant current to the resistor in the second inspection mode.

  According to this configuration, in the second inspection mode in which the presence / absence of the short-circuit state is determined, the current flowing through the resistor is increased, and the amplitude of the output voltage of the amplifier circuit is increased. The threshold voltage difference can be increased, and the accuracy of the determination of the short state is improved.

  Preferably, the amplifying circuit sets the magnitude of the gain in the first inspection mode to a first value, and sets the magnitude of the gain in the second inspection mode to a second value larger than the first value. Set.

  According to this configuration, the gain of the amplifier circuit is increased and the amplitude of the output voltage of the amplifier circuit is increased in the second inspection mode in which the presence or absence of the short-circuit state is determined. The threshold voltage difference can be increased, and the accuracy of the determination of the short state is improved.

  Preferably, each of the first comparator and the second comparator is a comparator having a hysteresis characteristic, and the second comparator has a hysteresis width that is a voltage difference of an input necessary for inversion of an output signal of a comparison result as the first comparator. Larger than one comparator.

  According to this configuration, even if the amplitude of the output voltage of the amplifier circuit is increased in the second inspection mode and the amplitude of noise is increased, the hysteresis width of the second comparator is large. (2) The sensitivity of the comparator is lowered, and it is difficult to make an erroneous determination of the presence or absence of the short state.

  A second aspect of the present invention relates to a load driving device capable of inspecting an open state and a short state of a resistor provided in a path of a current flowing by driving a load. In the normal operation mode, the load driving device amplifies a voltage generated in the resistor, a current output circuit that outputs a current corresponding to an input signal to the load, and outputs a voltage obtained by adding a reference voltage to the amplification result An amplifying circuit, a first comparator that compares an output voltage of the amplifying circuit and a first threshold voltage set as a determination condition of the open state, an output voltage of the amplifying circuit, and determination of the short-circuit state Based on the second comparator that compares the second threshold voltage set as a condition, the output signal of the first comparator, and the output signal of the second comparator, the presence or absence of the open state is determined in the first inspection mode. And a determination circuit for determining the presence or absence of the short state in the second inspection mode. The amplifier circuit inverts the polarity of the gain between the first inspection mode and the second inspection mode. The reference voltage is a voltage between the first threshold voltage and the second threshold voltage. The current output circuit operates as a current source that outputs a current flowing in one direction to the resistor in the first inspection mode and the second inspection mode.

  According to this configuration, the current output circuit that outputs current to the load in the normal operation mode operates as a current source that outputs current to the load in the first inspection mode and the second inspection mode. Therefore, the circuit configuration can be simplified as compared with the case where an independent current source is provided for the inspection mode.

  Preferably, the current output circuit operates as the current source that outputs a first constant current to the resistor in the first inspection mode, and is larger than the first constant current in the resistor in the second inspection mode. It operates as the current source that outputs the second constant current.

  Preferably, the current output circuit includes an output stage including at least one output transistor for controlling a current flowing through the load in the normal operation mode, and the output transistor included in the output stage in the normal operation mode. In the first inspection mode and the second inspection mode, the output transistor of the output stage is disconnected from the first transistor driving circuit, and at least one of the disconnected output transistors is And a second transistor drive circuit for driving the part to operate as the current source.

  According to this configuration, the output transistor of the output stage that controls the current flowing through the load in the normal operation mode is driven to operate as the current source in the first inspection mode and the second inspection mode. The Therefore, the circuit configuration can be simplified as compared with the case where an independent current source is provided for the inspection mode.

  Preferably, the second transistor drive circuit includes a current mirror transistor that forms a current mirror circuit together with the output transistor in the first inspection mode and the second inspection mode.

  According to this configuration, an accurate current is supplied to the resistor by the current mirror circuit.

  Preferably, the second transistor drive circuit sets a current flowing through the current mirror transistor to a first reference current in the first inspection mode, and a current flowing through the current mirror transistor in the second inspection mode. Is set to a second reference current larger than the first reference current.

  According to this configuration, the current flowing through the current mirror transistor is switched between the first reference current and the second reference current, so that the current flowing through the resistor is the first constant current and the second constant current. Switch to

  Preferably, the amplifying circuit sets the magnitude of the gain in the first inspection mode to a first value, and sets the magnitude of the gain in the second inspection mode to a second value larger than the first value. Set.

  Preferably, each of the first comparator and the second comparator is a comparator having a hysteresis characteristic, and the second comparator has a hysteresis width that is a voltage difference of an input necessary for inversion of an output signal of a comparison result as the first comparator. Larger than one comparator.

  Preferably, the load driving device includes a threshold voltage control circuit that controls a threshold voltage input to the first comparator and the second comparator. The threshold voltage control circuit inputs the first threshold voltage to the first comparator and the second threshold voltage to the second comparator in the first inspection mode and the second inspection mode. In the normal operation mode, a third threshold voltage is input to the first comparator and a fourth threshold voltage is input to the second comparator. In the normal operation mode, the determination circuit is configured to change the output voltage of the amplifier circuit from the third threshold voltage to the fourth threshold voltage based on the output signal of the first comparator and the output signal of the second comparator. When it deviates from the range up to the voltage, it is determined as an abnormal state.

  According to the above configuration, the determination circuit that determines the open state and the short state in the first inspection mode and the second inspection mode also determines the output voltage of the amplifier circuit in the normal operation mode. It is also used. This simplifies the configuration as compared with the case where a dedicated circuit is provided for determining the output voltage of the amplifier circuit in the normal operation mode.

  According to the present invention, an open state and a short state of a resistor can be accurately inspected with a simple configuration.

It is a figure showing an example of composition of a load drive concerning an embodiment of the present invention, and shows a state of a circuit in the 1st inspection mode and the 2nd inspection mode. It is a figure which shows an example of a structure of the load drive device which concerns on embodiment of this invention, and shows the state of the circuit in normal operation mode. It is a figure which shows an example of a structure of an amplifier circuit, and shows the state of the circuit in 1st test | inspection mode and 2nd test | inspection mode. It is a figure which shows an example of a structure of an amplifier circuit, and shows the state of the circuit in normal operation mode. It is a figure for demonstrating the relationship between the output voltage of the amplifier circuit in 1st test | inspection mode and 2nd test | inspection mode, and a determination result. It is a figure for demonstrating the relationship between the output voltage of the amplifier circuit in a normal operation mode, and a determination result. It is a figure which shows an example of a structure of the open / short detection circuit which concerns on embodiment of this invention.

  FIG.1 and FIG.2 is a figure which shows an example of a structure of the load drive device 1 which concerns on embodiment of this invention. A load driving device 1 shown in FIGS. 1 and 2 is a device that supplies a current IL to a load L1 to be driven, and includes a current output circuit 10, a detection circuit 20, and a resistor Rs. In the illustrated example, the load L1 is an inductor, but other types of loads may be used.

  The current output circuit 10 and the detection circuit 20 are, for example, integrated circuits formed on a semiconductor chip. The current output circuit 10 and the detection circuit 20 may be formed on the same semiconductor chip or may be formed on different semiconductor chips.

  The resistor Rs is provided on the path of the current IL that flows by driving the load L1. The load driving device 1 detects the current IL based on the voltage generated in the resistor Rs. The load driving device 1 has two inspection modes (a first inspection mode and a second inspection mode) for inspecting the state of the resistor Rs in addition to the normal operation mode in which the load L1 is driven. The load driving device 1 inspects the open state of the resistor Rs in the first inspection mode, and inspects the short state of the resistor Rs in the second inspection mode. FIG. 1 shows circuit states (switches, threshold voltages, etc.) in the first inspection mode and the second inspection mode, and FIG. 2 shows circuit states in the normal operation mode.

  The current output circuit 10 outputs a current IL corresponding to the input signal Vin to the load L1 in the normal operation mode, and outputs a current flowing in one direction to the resistor Rs in the first inspection mode and the second inspection mode. The current output circuit 10 outputs the first constant current I1 in the first inspection mode for inspecting the open state of the resistor Rs, and outputs the second constant current I2 in the second inspection mode for inspecting the short state of the resistor Rs. The second constant current I2 is larger than the first constant current I1. When the short state is inspected, a larger current IL flows through the resistor Rs than when the open state is inspected.

  In the illustrated example, the current output circuit 10 includes an output stage 11, a first transistor drive circuit 12, and a second transistor drive circuit 13.

  The output stage 11 includes four output transistors M1 to M4 that control the current flowing through the load L1 in the normal operation mode. In the illustrated example, the output transistors M1 to M4 form an H bridge, and a bidirectional current IL can flow through the load L1. The output transistors M1 and M3 are p-type MOS transistors, and the output transistors M2 and M4 are n-type MOS transistors. The output transistors M1 and M2 are connected in series between the power supply VDD and the ground, and the connection midpoint (the drains of the output transistors M1 and M2) is connected to the terminal T3. The source of the output transistor M1 is connected to the power supply VDD, and the source of the output transistor M2 is connected to the ground. The output transistors M3 and M4 are connected in series between the power supply VDD and the ground, and the connection midpoint (the drains of the output transistors M3 and M4) is connected to the terminal T4. The source of the output transistor M3 is connected to the power supply VDD, and the source of the output transistor M4 is connected to the ground. A load L1 and a resistor R are connected in series between the terminal T3 and the terminal T4.

  The first transistor drive circuit 12 drives the four output transistors M1 to M4 included in the output stage 11 in the normal operation mode. The first transistor drive circuit 12 supplies a drive voltage to the gates of the output transistors M1 to M4 constituting the H bridge. The first transistor drive circuit 12 controls the output transistors M1 to M4 so that a current corresponding to the signal Vi input between the terminals T1 and T2 flows to the load L1.

  The second transistor drive circuit 13 separates the output transistors M1 to M4 of the output stage 11 from the first transistor drive circuit 12 in the first test mode and the second test mode, respectively. Then, the second transistor drive circuit 13 drives the two transistors so that the output transistors M1 and M4 separated from the first transistor drive circuit 12 operate as a current source for flowing a current in one direction to the resistor Rs.

  The second transistor drive circuit 13 includes switches SW1 to SW6, a current mirror transistor M5, and a reference current setting circuit 121 in the illustrated example.

  The switches SW1 to SW4 are provided in a path for inputting a drive voltage from the first transistor drive circuit 12 to the output transistors M1 to M4, and are turned off in the first inspection mode and the second inspection mode (FIG. 1) and are operated normally. Turns on in mode (FIG. 2).

  The current mirror transistor M5 forms a current mirror circuit together with the output transistor M1 in the first inspection mode and the second inspection mode. In the illustrated example, the current mirror transistor M5 is a p-type MOS transistor, the source is connected to the power supply VDD, and the drain and gate are connected to the gate of the output transistor M1 via the switch SW5. The switch SW5 is turned on in the first inspection mode and the second inspection mode (FIG. 1), and is turned off in the normal operation mode (FIG. 2).

  The reference current setting circuit 121 sets the current flowing through the current mirror transistor M5 to the first reference current Ir1 in the first inspection mode, and the current flowing through the current mirror transistor M5 in the second inspection mode. The second reference current Ir2 is set to be larger than Ir1. The reference current setting circuit 121 includes, for example, a constant current circuit that allows the first reference current Ir1 or the second reference current Ir2 to flow to the drain of the current mirror transistor M5.

  The switch SW6 is connected between the gate of the output transistor M4 and the power supply VDD, and is turned on in the first inspection mode and the second inspection mode (FIG. 1) and turned off in the normal operation mode (FIG. 2).

  The detection circuit 20 detects the current IL based on the voltage of the resistor Rs, and determines whether there is an abnormality such as an open state or a short state of the resistor Rs based on the voltage of the resistor Rs. In the illustrated example, the detection circuit 20 includes an amplification circuit 21, a first comparator CP1, a second comparator CP2, a determination circuit 22, and a threshold voltage control circuit 23.

  The amplifier circuit 21 amplifies the voltage generated in the resistor Rs, and outputs a voltage Vamp obtained by adding a predetermined reference voltage to the amplification result. In one example, the amplifier circuit 21 sets the reference voltage in the first inspection mode and the second inspection mode to “Vref” and the reference voltage in the normal operation mode to “Vcom”. The reference voltages Vref and Vcom may be the same value.

  The amplifier circuit 21 inverts the polarity of the gain in the first inspection mode and the second inspection mode, and sets the gain magnitude “A2” in the second inspection mode from the gain magnitude “A1” in the first inspection mode. Set to a larger value. The amplifier circuit 21 sets the magnitude of the gain in the normal operation mode to “An”.

  The output voltage Vamp of the amplifier circuit 21 in each operation mode is expressed by the following equation, for example. However, “Rs” indicates the resistance value of the resistor Rs, and “IL” indicates the current flowing through the resistor Rs in the normal operation mode.

First inspection mode (open inspection mode):
Vamp = Vref−A1 · I1 · Rs (1)

Second inspection mode (short inspection mode):
Vamp = Vref + A2 · I2 · Rs (2)

Normal operation mode:
Vamp = Vcom + An · IL · Rs (3)

  3 and 4 are diagrams illustrating an example of the configuration of the amplifier circuit 21. FIG. FIG. 3 shows a circuit state in the first inspection mode and the second inspection mode, and FIG. 4 shows a circuit state in the normal operation mode. In the illustrated example, the amplifier circuit 21 includes an operational amplifier OP1, a polarity inverting circuit X1, resistors R1 to R6, and switches SW7 to SW12.

  Between the inverting input terminal (−) and the output terminal of the operational amplifier OP1, a resistor R3 and a switch SW7 are connected in series, and a resistor R4 and a switch SW8 are connected in series.

  Between the non-inverting input terminal (+) of the operational amplifier OP1 and the node N1, a resistor R5 and a switch SW9 are connected in series, and a resistor R6 and a switch SW10 are connected in series.

  A reference voltage Vref is applied to the node N1 through the switch SW11, or a reference voltage Vcom is applied through the switch SW12.

  The inverting input terminal (−) of the operational amplifier OP1 is connected to the terminal T5 or T6 via the resistor R1 and the polarity inverting circuit X1. The non-inverting input terminal (+) of the operational amplifier OP1 is connected to the terminal T5 or T6 via the resistor R2 and the polarity inverting circuit X1. Terminals T5 and T6 are connected to both ends of the resistor Rs.

  The polarity inverting circuit X1 is a switch that connects the terminals T5 and T6 and one ends of the resistors R1 and R2 on a one-to-one basis, and reverses the connection relationship between the first inspection mode and the second inspection mode.

  In the first test mode (open test mode), the polarity inverting circuit X1 connects one end of the resistor R1 to the terminal T5 and connects one end of the resistor R2 to the terminal T6. On the other hand, the polarity inverting circuit X1 connects one end of the resistor R1 to the terminal T6 and connects one end of the resistor R2 to the terminal T5 in the second inspection mode (short-circuit inspection mode). In the normal operation mode, the polarity inverting circuit X1 connects one end of the resistor R1 to the terminal T6 and connects one end of the resistor R2 to the terminal T5.

  In the first inspection mode and the second inspection mode, as shown in FIG. 3, the switches SW7, SW9, SW11 are turned on, and the switches SW8, SW10, SW12 are turned off. In this case, the reference voltage Vref is applied to the node N1, and resistors R3 and R5 are connected to the operational amplifier OP1. The resistors R3 and R5 are variable resistors, and the resistance value in the second inspection mode is larger than that in the first inspection mode. As a result, the gain magnitude “A2” in the second inspection mode becomes larger than the gain magnitude “A1” in the first inspection mode.

  In the example of FIGS. 3 and 4, the voltage Vr of the resistor Rs is defined based on the potential of the terminal T6. In the first inspection mode, one end of the resistor R1 is connected to the terminal T5 by the polarity inversion circuit X1, and one end of the resistor R2 is connected to the terminal T6. Therefore, the gain polarity of the amplifier circuit 21 that amplifies the voltage Vr is The gain including the polarity is “−A1” (formula (1)). On the other hand, in the second inspection mode, since one end of the resistor R1 is connected to the terminal T6 and one end of the resistor R2 is connected to the terminal T5 by the polarity inversion circuit X1, the gain of the amplifier circuit 21 that amplifies the voltage Vr is increased. The polarity is positive, and the gain including the polarity is “+ A2” (formula (2)).

  In the normal operation mode, as shown in FIG. 4, the switches SW7, SW9, SW11 are turned off, and the switches SW8, SW10, SW12 are turned on. In this case, the reference voltage Vcom is applied to the node N1, and resistors R4 and R6 having a certain resistance value are connected to the operational amplifier OP1. The resistance values of the resistors R4 and R6 are set so that, for example, the magnitude of the gain of the amplifier circuit 21 is included in the range from “A1” to “A2”. In the normal operation mode, one end of the resistor R1 is connected to the terminal T6 by the polarity inverting circuit X1, and one end of the resistor R2 is connected to the terminal T5. Therefore, the gain polarity of the amplifier circuit 21 that amplifies the voltage Vr is positive. Thus, the gain including the polarity is “+ An” (formula (3)).

  The first comparators CP1 and CP2 compare the threshold voltage input from the threshold voltage control circuit 23 with the output voltage Vamp of the amplifier circuit 21, and output a signal corresponding to the comparison result.

  In the first test mode and the second test mode, the first comparator CP1 compares the output voltage Vamp of the amplifier circuit 21 with the first threshold voltage Vo set as a determination condition for the open state of the resistor Rs (FIG. 1). The first comparator CP1 outputs a high level signal when the voltage Vamp is higher than the first threshold voltage Vo, and outputs a low level signal when the voltage Vamp is lower than the first threshold voltage Vo. To do. When the resistor Rs is in an open state, the output signal of the first comparator CP1 is at a low level in the first inspection mode.

  The first comparator CP1 compares the output voltage Vamp of the amplifier circuit 21 with the third threshold voltage VL on the low voltage side in the normal operation mode (FIG. 2). The first comparator CP1 outputs a high level signal when the voltage Vamp is higher than the third threshold voltage VL, and outputs a low level signal when the voltage Vamp is lower than the third threshold voltage VL. To do. When the voltage Vamp decreases outside the normal range in the normal operation mode, the output signal of the first comparator CP1 becomes low level.

  In the first inspection mode and the second inspection mode, the second comparator CP2 compares the output voltage Vamp of the amplifier circuit 21 with the second threshold voltage Vs set as the determination condition for the short state of the resistor Rs (FIG. 1). The second comparator CP2 outputs a high level signal when the voltage Vamp is lower than the second threshold voltage Vs, and outputs a low level signal when the voltage Vamp is higher than the second threshold voltage Vs. To do. When the resistor Rs is in a short state, the output signal of the second comparator CP2 becomes high level in the second inspection mode.

  The second comparator CP2 compares the output voltage Vamp of the amplifier circuit 21 with the fourth threshold voltage VH on the high voltage side in the normal operation mode (FIG. 2). The second comparator CP2 outputs a high level signal when the voltage Vamp is lower than the fourth threshold voltage VH, and outputs a low level signal when the voltage Vamp is higher than the fourth threshold voltage VH. To do. When the voltage Vamp increases outside the normal range in the normal operation mode, the output signal of the second comparator CP2 becomes low level.

  In the present embodiment, the first comparator CP1 and the second comparator CP2 are each comparators having hysteresis characteristics. The second comparator CP2 that determines the short state has a larger hysteresis width than the first comparator CP1, which is a voltage difference between the inputs necessary to invert the output signal of the comparison result. Since the second comparator CP2 has a larger hysteresis width than the first comparator CP1, the sensitivity to noise is low.

  The threshold voltage control circuit 23 controls the threshold voltage input to the first comparator CP1 and the second comparator CP2. The threshold voltage control circuit 23 inputs the first threshold voltage Vo to the first comparator CP1 and the second threshold voltage Vs to the second comparator CP2 in the first inspection mode and the second inspection mode. In the operation mode, the third threshold voltage VL is input to the first comparator CP1, and the fourth threshold voltage VH is input to the second comparator CP2.

  The determination circuit 22 determines whether or not the resistor Rs is open in the first inspection mode based on the output signal of the first comparator CP1 and the output signal of the second comparator CP2, and short-circuits the resistor Rs in the second inspection mode. Determine if there is a condition. Specifically, the determination circuit 22 determines that the resistor Rs is in an open state when the output signal of the first comparator CP1 is low in the first inspection mode, and outputs the second comparator CP2 in the second inspection mode. When the signal is at a high level, it is determined that the resistor Rs is in a short state.

  In the normal operation mode, the determination circuit 22 sets the output voltage Vamp of the amplifier circuit 21 from the third threshold voltage VL to the fourth threshold voltage VL based on the output signal of the first comparator CP1 and the output signal of the second comparator CP2. When it deviates from the range up to the threshold voltage VH, it is determined as an abnormal state. Specifically, the determination circuit 22 determines an abnormal state when at least one of the output signal of the first comparator CP1 and the output signal of the second comparator CP2 is at a low level.

  The determination circuit 22 is configured by, for example, a NAND circuit that calculates a negative logical product of the output signal of the first comparator CP1 and the output signal of the second comparator CP2. The output signal Sf of the NAND circuit indicates the open state of the resistor Rs when it is high in the first inspection mode, indicates the short state of the resistor Rs when it is low in the second inspection mode, and is high in the normal operation mode. In this case, the abnormality of the voltage Vamp is indicated.

  Here, operation | movement of the load drive device 1 which concerns on this embodiment which has the structure mentioned above is demonstrated.

(First inspection mode, second inspection mode)
In the first inspection mode and the second inspection mode, as shown in FIG. 1, the switches SW1 to SW4 are turned off and the switches SW5 and SW6 are turned on. As a result, a current mirror circuit is formed by the current mirror transistor M5 and the output transistor M1, and the output transistor M4 is turned on. The current IL generated by the current mirror circuit is unidirectional and flows from the power supply VDD to the ground through the load L1 and the resistor Rs. In the amplifier circuit 21, the voltage Vr generated in the resistor Rs is amplified by the current IL, and a voltage Vamp obtained by adding the reference voltage Vref to the amplification result is output.

  FIG. 5 is a diagram for explaining the relationship between the output voltage Vamp of the amplifier circuit 21 and the determination result in the first inspection mode and the second inspection mode. The horizontal axis represents the resistance value of the resistor Rs, and the vertical axis represents the output voltage Vamp of the amplifier circuit 21. A straight line W1 indicates a proportional relationship between the resistance value Rs and the voltage Vamp in the first inspection mode, and a straight line W2 indicates a proportional relationship between the resistance value Rs and the voltage Vamp in the second inspection mode.

  In the first inspection mode, since the gain polarity of the amplifier circuit 21 is negative, the voltage Vamp decreases with respect to the reference voltage Vref as the resistance value Rs increases as shown by the straight line W1 in FIG. The voltage Vamp is always lower than the reference voltage Vref, and the output signal of the second comparator CP2 is always high. When the voltage Vamp becomes lower than the first threshold voltage Vo, the resistance value Rs becomes larger than “Ropen”. In this case, since the output signal of the first comparator CP1 is at a low level, the determination circuit 22 outputs a high level signal Sf indicating an open state.

  In the second inspection mode, since the gain polarity of the amplifier circuit 21 is positive, the voltage Vamp increases with respect to the reference voltage Vref as the resistance value Rs increases as shown by the straight line W2 in FIG. The voltage Vamp is always higher than the reference voltage Vref, and the output signal of the first comparator CP1 is always high. When the voltage Vamp becomes lower than the second threshold voltage Vs, the resistance value Rs becomes smaller than “Rshort”. In this case, since the output signal of the second comparator CP2 becomes high level, the determination circuit 22 outputs a low level signal Sf indicating a short state.

  The second constant current I2 output from the current output circuit 10 in the second inspection mode is larger than the first constant current I1 in the first inspection mode, and the gain “A2” of the amplifier circuit 21 in the second inspection mode. Is larger than “A1” in the second inspection mode. Therefore, as shown in FIG. 5, the slope of the straight line W1 is larger than the straight line W2. That is, since the minute resistance value Rs is determined in the second inspection mode, the gain and current output of the amplifier circuit 21 are increased so that the amplitude of the output voltage Vamp of the amplifier circuit 21 (the component of the amplification result of the voltage Vr) increases. The current value of the circuit 10 is set.

(Normal operation mode)
In the normal operation mode, as shown in FIG. 2, the switches SW1 to SW4 are turned on, and the switches SW5 and SW6 are turned off. As a result, drive voltages are respectively input from the first transistor drive circuit 12 to the output transistors M1 to M4, and a bidirectional current IL corresponding to the input signal Vi flows through the load L1. In the amplifier circuit 21, the voltage Vr generated in the resistor Rs is amplified by the current IL, and a voltage Vamp obtained by adding the reference voltage Vcom to the amplification result is output.

  FIG. 6 is a diagram for explaining the relationship between the output voltage Vamp of the amplifier circuit 21 and the determination result in the normal operation mode. The horizontal axis represents time, and the vertical axis represents the output voltage Vamp of the amplifier circuit 21. As shown in FIG. 6, when the voltage Vamp is lower than the third threshold voltage VL or higher than the fourth threshold voltage VH, the determination circuit 22 outputs a high level signal Sf indicating an abnormality of the voltage Vamp. The

  As described above, according to the present embodiment, independent comparators are used for the determination of the open state and the determination of the short state, and these two determinations are individually performed in the independent inspection mode. As a result, conditions suitable for each determination can be set, so that the determination accuracy can be easily improved.

  According to the present embodiment, the current output circuit 10 (current source of the current IL), the amplifier circuit 21, and the determination circuit 22 are commonly used in the first inspection mode and the second inspection mode. Therefore, the circuit configuration can be simplified compared to the case where dedicated test circuits are provided for the open state determination and the short state determination, respectively.

  According to the present embodiment, the current IL flows through the resistor Rs in one direction in the first inspection mode and the second inspection mode, whereas the gain polarity of the amplifier circuit 21 is inverted in these two inspection modes. That is, in the first inspection mode, as the resistance value of the resistor Rs increases, the output voltage Vamp of the amplifier circuit 21 becomes lower than the reference voltage Vref and does not become higher than the reference voltage Vref. In the second inspection mode, as the resistance value of the resistor Rs increases, the output voltage Vamp of the amplifier circuit 21 becomes higher than the reference voltage Vref and does not become lower than the reference voltage Vref. Since the reference voltage Vref is a voltage between the first threshold voltage Vo and the second threshold voltage Vs, in the first inspection mode in which the presence or absence of the open state is determined by the output signal of the first comparator CP1, amplification is performed. Regardless of the output voltage Vamp of the circuit 21, the output signal of the second comparator CP2 is always at a high level. In the second inspection mode in which the presence or absence of a short state is determined by the output signal of the second comparator CP2, the output signal of the first comparator CP1 is always at a high level regardless of the output voltage Vamp of the amplifier circuit 21. That is, in each inspection mode, the output signal of one of the two comparators (first comparator CP1 and second comparator CP2) is always at a high level. Accordingly, the determination circuit 22 can obtain the determination results of the two inspection modes with a simple circuit configuration (with one NAND circuit in the example of FIG. 1) based on the output signals of the two comparators.

  According to the present embodiment, the current flowing through the resistor Rs increases in the second inspection mode in which the presence or absence of a short state is determined, and the amplitude of the output voltage Vamp of the amplifier circuit 21 increases. Therefore, the difference between the second threshold voltage Vs and the reference voltage Vref can be increased, and the accuracy of determining a short state can be improved.

  According to the present embodiment, the gain of the amplifier circuit 21 is increased and the amplitude of the output voltage Vamp of the amplifier circuit 21 is increased in the second inspection mode in which the presence / absence of a short state is determined. The difference in threshold voltage Vs can be increased, and the accuracy of determination of a short state can be improved.

  According to the present embodiment, even if the amplitude of the noise increases due to an increase in the amplitude of the output voltage Vamp of the amplifier circuit 21 in the second inspection mode (the sensitivity of the amplifier circuit 21 increases), the second comparator CP2 Since a relatively large hysteresis width is set, the sensitivity of the second comparator CP2 to noise becomes low. As a result, it is possible to make it difficult to erroneously determine the presence or absence of a short state.

  According to the present embodiment, the current output circuit 10 that outputs the current IL to the load L1 in the normal operation mode operates as a current source that outputs the inspection current IL to the load L1 in the first inspection mode and the second inspection mode. To do. Therefore, the circuit configuration can be simplified as compared with the case where an independent current source is provided for the inspection mode.

  According to the present embodiment, the output transistors M1 and M4 of the output stage 11 that control the current IL flowing through the load L1 in the normal operation mode cause the unidirectional constant current (in one direction to the load L1 in the first inspection mode and the second inspection mode). Driven to operate as a current source that outputs I1 or I2). Therefore, the circuit configuration can be simplified as compared with the case where an independent current source is provided for the inspection mode. Further, when the current output circuit 10 is formed as an integrated circuit on a semiconductor chip, the output transistors M1 and M4 used for controlling the current IL in the normal operation mode have a relatively large size so as to obtain high ESD resistance. A transistor with is used. If an independent current source is provided for the test mode, this large size transistor must be added separately. On the other hand, according to the present embodiment, since the output transistors M1 and M4 are also used as current sources in the inspection mode, an increase in circuit size can be suppressed.

  According to the present embodiment, the determination circuit 22 that determines the open state and the short state in the first inspection mode and the second inspection mode is also used for the determination of the output voltage Vamp of the amplifier circuit 21 in the normal operation mode. Thereby, the circuit configuration can be simplified as compared with the case where a dedicated circuit is provided for determining the voltage Vamp in the normal operation mode.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to said embodiment, Various variations are included.

  In the embodiment described above, the current output circuit 10 of the load driving device 1 is used as a current source in the first inspection mode and the second inspection mode, but the present invention is not limited to this example. That is, the present invention can be applied to an open / short inspection circuit having an independent current source and inspecting an open state and a short state of a resistor in an arbitrary device.

  FIG. 7 is a diagram showing an example of the configuration of the open / short detection circuit 2 according to the embodiment of the present invention. The open / short detection circuit 2 shown in FIG. 7 detects an open state and a short state of the resistor Rs connected in series with the load L1. The open / short detection circuit 2 supplies current to the load L1 in the first inspection mode and the second inspection mode independently of the current output circuit 5 that outputs the current IL corresponding to the input signal Vi to the load L1 in the normal operation mode. A current source I5 that outputs IL is provided. The current source I5 outputs a first constant current I1 in the first inspection mode, and outputs a second constant current I2 in the second inspection mode. In addition to the current source I5, the open / short detection circuit 2 has the same components (amplifier circuit 21, first comparator CP1, second comparator CP2, threshold voltage) as the load driving device 1 shown in FIGS. A control circuit 23 and a determination circuit 22). Also in the open / short detection circuit 2 shown in FIG. 7, the same effects as those of the above-described embodiment can be obtained.

  The circuit configuration in the above-described embodiment is an example and may be replaced with another circuit having an equivalent function.

  DESCRIPTION OF SYMBOLS 1 ... Load drive device, 10 ... Current output circuit, 11 ... Output stage, 12 ... 1st transistor drive circuit, 121 ... Reference current setting circuit, 13 ... 2nd transistor drive circuit, 20 ... Detection circuit, 21 ... Amplifier circuit, DESCRIPTION OF SYMBOLS 22 ... Judgment circuit, 23 ... Threshold voltage control circuit, CP1 ... 1st comparator, CP2 ... 2nd comparator, M1-M4 ... Output transistor, M5 ... Current mirror transistor, SW1-SW12 ... Switch, X1 ... Polarity inversion circuit , OP1, operational amplifier, Rs, resistor, R1 to R6, resistor, L1, load, Vo, first threshold voltage, Vs, second threshold voltage, VL, third threshold voltage, VH, fourth threshold voltage. , I1 ... first constant current, I2 ... second constant current, Ir1 ... first reference current, Ir2 ... second reference current, Vref, Vcom ... reference voltage.

Claims (12)

An open / short inspection circuit for inspecting an open state and a short state of a resistor,
A current source that outputs current flowing in one direction to the resistor;
An amplification circuit that amplifies the voltage generated in the resistor and outputs a voltage obtained by adding a reference voltage to the amplification result;
A first comparator for comparing the output voltage of the amplifier circuit with a first threshold voltage set as a determination condition for the open state;
A second comparator for comparing the output voltage of the amplifier circuit with a second threshold voltage set as a determination condition for the short state;
A determination circuit for determining whether or not the open state is present in the first inspection mode and determining whether or not the short state is present in the second inspection mode based on the output signal of the first comparator and the output signal of the second comparator; Have
The amplifier circuit reverses the polarity of the gain in the first inspection mode and the second inspection mode,
The reference voltage is a voltage between the first threshold voltage and the second threshold voltage.
Open / short inspection circuit. The current source outputs a first constant current to the resistor in the first inspection mode, and outputs a second constant current larger than the first constant current to the resistor in the second inspection mode.
The open / short inspection circuit according to claim 1. The amplifier circuit sets the magnitude of the gain in the first inspection mode to a first value, and sets the magnitude of the gain in the second examination mode to a second value larger than the first value;
The open / short inspection circuit according to claim 1 or 2. The first comparator and the second comparator are comparators having hysteresis characteristics,
The second comparator has a larger hysteresis width, which is a voltage difference between inputs required for inverting the output signal of the comparison result, than the first comparator.
4. The open / short inspection circuit according to claim 2 or 3. A load driving device capable of inspecting an open state and a short state of a resistor provided in a path of a current flowing by driving a load,
A current output circuit for outputting a current corresponding to an input signal to the load in a normal operation mode;
An amplification circuit that amplifies the voltage generated in the resistor and outputs a voltage obtained by adding a reference voltage to the amplification result;
A first comparator for comparing the output voltage of the amplifier circuit with a first threshold voltage set as a determination condition for the open state;
A second comparator for comparing the output voltage of the amplifier circuit with a second threshold voltage set as a determination condition for the short state;
A determination circuit for determining whether or not the open state is present in the first inspection mode and determining whether or not the short state is present in the second inspection mode based on the output signal of the first comparator and the output signal of the second comparator; Have
The amplifier circuit reverses the polarity of the gain in the first inspection mode and the second inspection mode,
The reference voltage is a voltage between the first threshold voltage and the second threshold voltage;
The current output circuit operates as a current source that outputs a current flowing in one direction to the resistor in the first inspection mode and the second inspection mode.
Load drive device. The current output circuit operates as the current source that outputs a first constant current to the resistor in the first inspection mode, and in the second inspection mode, a second constant larger than the first constant current is applied to the resistor. Operating as the current source for outputting current,
The load driving device according to claim 5. The current output circuit is
An output stage including at least one output transistor for controlling a current flowing through the load in the normal operation mode;
A first transistor driving circuit for driving each of the output transistors included in the output stage in the normal operation mode;
In the first inspection mode and the second inspection mode, the output transistors of the output stage are disconnected from the first transistor drive circuit, and at least a part of the disconnected output transistors is operated as the current source. A second transistor drive circuit that
The load driving device according to claim 6. The second transistor drive circuit includes a current mirror transistor that forms a current mirror circuit together with the output transistor in the first inspection mode and the second inspection mode.
The load driving device according to claim 7. The second transistor drive circuit sets a current flowing through the current mirror transistor to a first reference current in the first inspection mode, and a current flowing through the current mirror transistor in the second inspection mode. Including a reference current setting circuit for setting a second reference current greater than one reference current;
The load driving device according to claim 8. The amplifier circuit sets the magnitude of the gain in the first inspection mode to a first value, and sets the magnitude of the gain in the second examination mode to a second value larger than the first value;
The load driving device according to any one of claims 5 to 9. The first comparator and the second comparator are comparators having hysteresis characteristics,
The second comparator has a larger hysteresis width, which is a voltage difference between inputs required for inverting the output signal of the comparison result, than the first comparator.
The load driving device according to any one of claims 6 to 10. A threshold voltage control circuit for controlling a threshold voltage input to the first comparator and the second comparator, wherein the first threshold is supplied to the first comparator in the first inspection mode and the second inspection mode. The second threshold voltage is input to the second comparator and the third threshold voltage is input to the first comparator and the fourth threshold voltage to the second comparator in the normal operation mode. A threshold voltage control circuit for inputting
In the normal operation mode, the determination circuit is configured to change the output voltage of the amplifier circuit from the third threshold voltage to the fourth threshold voltage based on the output signal of the first comparator and the output signal of the second comparator. When it deviates from the range up to the voltage, it is determined as an abnormal state.
The load driving device according to any one of claims 5 to 11.

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