JP2011142554A - Disconnection detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize an influence of unnecessary components such as noise to detect disconnection with high reliability. <P>SOLUTION: A load M, a MOS transistor M1, and a resistor R1 are connected in series between a power supply Vc and the ground. A first voltage detection circuit 3 detects terminal voltage of the resistor R1. A control circuit 2 detects the disconnection based on a detection result obtained by comparing the detected voltage of the resistor R1 detected by the first voltage detection circuit 3 with threshold voltage ref1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a disconnection detection circuit for detecting disconnection of a load.

  For example, Patent Document 1 discloses a circuit that detects an abnormality such as disconnection of a load. In the technique of this Patent Document 1 (for example, FIG. 1), a load is connected in series to an open drain type output terminal of a MOS transistor (corresponding to a switching element). When disconnection occurs in this circuit, the voltage at the output terminal becomes “H” level via the pull-up resistor when the MOS transistor is off.

  In this technical idea, the disconnection is detected by detecting the “H” level. On the other hand, when the MOS transistor is on, the disconnection is detected by detecting that the voltage generated at the drain of the MOS transistor is above a certain level. According to the technical idea described in Patent Document 1, the detection voltage when the MOS transistor is on is determined by the on-resistance of the MOS transistor and the impedance of the load.

JP 2009-95150 A (FIG. 1)

  However, the on-resistance of the MOS transistor is generally low, and the voltage detection circuit detects the voltage at the common connection point between the MOS transistor and the load, compares it with a predetermined threshold voltage, and detects disconnection based on this detection result. However, the set voltage range of the threshold voltage becomes very narrow. Moreover, even if the set voltage range of the threshold voltage can be set appropriately, it is easily affected by unnecessary components such as noise, and there is a risk of malfunction.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a disconnection detection circuit capable of detecting disconnection with high reliability by suppressing the influence of unnecessary components such as noise as much as possible.

  According to the first aspect of the present invention, the first voltage detection circuit detects the voltage generated in the first detection element when the switching element is turned on by comparing with the threshold voltage, and the first voltage detection circuit detects the voltage generated when the switching element is turned off. 2 Since the voltage generated in the detection element is detected by comparing with the threshold voltage and the disconnection is detected based on the detection result of the first voltage detection circuit, it is less affected by unnecessary components such as noise and the disconnection is detected with high reliability. it can.

  According to the invention of claim 2, since the selection circuit selects either the detection result of the first or second voltage detection circuit, and detects the disconnection based on the detection result selected by the selection circuit, Various disconnection detection methods can be selected.

  According to the invention described in claim 3, since the bypass means bypasses the energization current of the first detection element while the detection result of the first voltage detection circuit is not acquired, the power consumption in the first detection element can be reduced.

  According to the invention of claim 4, the synchronization acquisition means acquires the detection result of the first voltage detection circuit in synchronization with the periodic signal when the switching element is on, and based on the acquisition result of the synchronization acquisition means Since the disconnection is detected, the disconnection can be detected every period of the periodic signal when the load is disconnected, and the disconnection can be detected quickly.

  According to the fifth aspect of the present invention, the bypass means is the first except for the period from when the first detection element is energized until the synchronization acquisition means acquires the detection result of the first voltage detection circuit in synchronization with the periodic signal. Since the energization current of one detection element is bypassed, power consumption by the first detection element can be reduced.

  According to the sixth aspect of the present invention, the first time when the bypass means bypasses the energization current of the first detection element is the detection result of the first voltage detection circuit after the synchronization acquisition means is energized to the first detection element. Is set longer than the second time until the signal is acquired in synchronization with the periodic signal, the power consumption by the first detection element can be reduced.

  According to the seventh aspect of the present invention, the energization current of the first detection element is bypassed except when the delay detection means acquires the detection result of the first voltage detection circuit after the first detection element is energized. Therefore, power consumption by the first detection element can be reduced.

According to the eighth aspect of the invention, since the first detection element includes one or more diodes, the disconnection can be detected stably regardless of the characteristics of the load.
According to the ninth aspect of the present invention, the first detection element includes one or more first diodes, and the threshold voltage to be compared by the first voltage detection circuit is a second voltage having the same characteristics as the first diode. Since it is generated using a diode, the temperature compensation of the first diode can be performed.

According to the tenth aspect of the invention, since the first and second diodes are integrated on one semiconductor chip, the characteristics of the first and second diodes can be easily made the same.
According to the eleventh aspect of the present invention, since the first detection element includes one or more first diodes integrated between the back gate and the drain of the MOS transistor, the MOS transistor and the first diode are provided. It becomes easy to form integrally by a semiconductor structure, and space saving can be achieved.

According to the twelfth aspect of the invention, since the first and second voltage detection circuits are shared, the circuit scale can be reduced, and downsizing and cost reduction can be achieved.
According to a thirteenth aspect of the present invention, the switching element and the bypass means are both constituted by MOS transistors electrically connected in common, and the MOS transistors are formed on the same semiconductor substrate, and are respectively formed by trench isolation. Therefore, the leakage between the switching element and the bypass means can be suppressed as much as possible.

1 is a schematic electrical configuration diagram of a disconnection detection circuit according to a first embodiment of the present invention. Timing chart during normal operation Timing chart when disconnection is detected FIG. 1 equivalent view in the second embodiment of the present invention. 2 equivalent diagram 3 equivalent figure Timing chart when the switching element drive output is turned off FIG. 1 equivalent view in the third embodiment of the present invention. 2 equivalent diagram 3 equivalent figure FIG. 1 equivalent view in the fourth embodiment of the present invention. FIG. 1 equivalent view in the fifth embodiment of the present invention. FIG. 1 equivalent view in the sixth embodiment of the present invention. FIG. 1 equivalent diagram in the seventh embodiment of the present invention FIG. 1 equivalent diagram in the eighth embodiment of the present invention (No. 1) Figure 1 equivalent (part 2)

(First embodiment)
A first embodiment in which the present invention is applied to a disconnection detection circuit of a low-side drive circuit will be described below with reference to FIGS.
FIG. 1 schematically shows a disconnection detection circuit in the low-side drive circuit.
As shown in FIG. 1, the low-side drive circuit A includes an N-channel type MOS transistor M1 as a switching element, and is configured by connecting a load M to a power source Vc via an output terminal N1 of the drain of the transistor M1. Has been. The gate (input terminal) of the transistor M1 is connected to the drive output terminal OUT of the control circuit 2. The control circuit 2 is constituted by a microcomputer, for example, and outputs a drive signal from the drive output terminal OUT to the gate of the MOS transistor M1.

  Between the power supply Vc and the ground, a load M, a drain-source of the transistor M1, and a resistor R1 as a first detection element are connected in series. The resistance value of the resistor R1 is set larger than the on-resistance of the transistor M1. An output terminal N1 serving as a common connection point between the source of the transistor M1 and the resistor R1 is connected to the first voltage detection circuit 3. The first voltage detection circuit 3 is set in advance so that the voltage corresponding to the current flowing through the resistor R1 when the transistor M1 is turned on can be compared with the threshold voltage ref1.

  The first voltage detection circuit 3 is configured by, for example, a comparator, compares the voltage at the common connection point N1 with the threshold voltage ref1, outputs “H” when the voltage exceeds the threshold voltage ref1, and outputs “L” when the voltage is equal to or lower than the threshold voltage ref1. Is output. The threshold voltage ref1 of the first voltage detection circuit 3 may be set according to the characteristics of the current flowing through the load M and the resistance value of the resistor R1 (impedance of the first detection element). For example, when the first detection element is configured by the resistor R1, the threshold voltage ref1 may be set to be equal to or lower than a voltage obtained by multiplying the required load current IL by the resistance value of the resistor R1. By adjusting the resistance value of the resistor R1, a noise margin can be easily secured.

  On the other hand, a common connection point N 2 between the drain of the transistor M 1 and the load M is connected to the second voltage detection circuit 4. The second voltage detection circuit 4 is configured by a comparator, for example, compares the voltage at the common connection point N2 with the threshold voltage ref2, outputs “H” when the voltage is lower than the threshold voltage ref2, and outputs “H” when the voltage exceeds the threshold voltage ref2. L "is output. A resistor R2 as a second detection element is connected between the common connection point N2 and the ground. The resistor R2 is set to a resistance value that is significantly larger than the impedance of the load M and the resistance value of the resistor R1.

  The outputs of the first voltage detection circuit 3 and the second voltage detection circuit 4 are given to the selection circuit 5. The selection circuit 5 is configured by combining, for example, a one-input inversion type AND gate 5a, an AND gate 5b, and an OR gate 5c, and the first voltage detection circuit 3 and the second voltage detection circuit according to the drive signal of the drive output terminal OUT. 4 is selected and the selection signal is output as a disconnection detection signal. The control circuit 2 detects the disconnection of the load M based on the diagnosis output signal that is the disconnection detection signal. In this way, the disconnection detection circuit 1 of the low-side drive circuit A is configured by connecting the control circuit 2, the transistor M1, the resistor R1, the first voltage detection circuit 3, the second voltage detection circuit 4, and the selection circuit 5 to each other. ing.

The operation of the above configuration will be described with reference to FIGS.
FIG. 2 shows a timing chart during normal operation (when the load is normally connected), and shows signal waveforms of essential parts when the low-side drive circuit A normally drives the load without detecting disconnection.

  As shown in FIG. 2A, the control circuit 2 outputs a rectangular wave signal from the output terminal OUT and applies it as a drive signal to the gate of the transistor M1. The transistor M1 is turned on / off, so that the load M is energized through the resistors R1 and R2 when the transistor M1 is turned on.

  The first voltage detection circuit 3 compares the voltage generated across the resistor R <b> 1 with the threshold voltage ref <b> 1 and outputs it to the selection circuit 5. At the timing of (1) in FIG. 2, when the detection voltage of the resistor R1 exceeds a predetermined threshold voltage ref1 as shown in FIG. 2 (b), the first voltage detection circuit 3 is shown in FIG. 2 (c). The output is switched from “H” to “L”.

  On the other hand, the second voltage detection circuit 4 compares the voltage of the output terminal N2 with the threshold voltage ref2 to detect and output it to the selection circuit 5. At the timing of (1) in FIG. 2, when the voltage at the output terminal N2 becomes equal to or lower than a predetermined threshold voltage ref2 as shown in FIG. 2 (d), the second voltage detection circuit 4 is shown in FIG. 2 (e). The output is switched from “L” to “H”.

  Since the selection circuit 5 validates the output signal of the first voltage detection circuit 3 and selectively outputs it to the control circuit 2 while the output signal OUT is “H”, the output OUT is output from the timing (1) in FIG. “L” is output as a diagnostic output until “L” is reached (timing (2) in FIG. 2).

  When the output OUT becomes “L”, the detection voltage of the resistor R1 gradually decreases and becomes equal to or lower than the threshold voltage ref1 (timing (3) in FIG. 2). At this time, the output of the first voltage detection circuit 3 changes from “L” to “H”. On the other hand, almost simultaneously with this timing, the voltage at the output terminal N2 gradually increases and exceeds the threshold voltage ref2. At this time, the output of the second voltage detection circuit 4 changes from “H” to “L”.

  The selection circuit 5 validates the output signal of the second voltage detection circuit 4 and selectively outputs it to the control circuit 2 while the output signal OUT is “L”. Therefore, “L” is output as the diagnosis output from the timing (3) in FIG. 2 until the output OUT becomes “H” (timing (4) in FIG. 2).

  Thereafter, when the output OUT becomes “H”, the detection voltage of the resistor R1 gradually increases and becomes a voltage exceeding the threshold voltage ref1. At this time, the output of the first voltage detection circuit 3 changes from “H” to “L”. On the other hand, almost simultaneously with this timing, the voltage at the output terminal N2 gradually decreases to a voltage equal to or lower than the threshold voltage ref2. At this time, the output of the second voltage detection circuit 4 changes from “L” to “H” (timing (5) in FIG. 2). Thereafter, the same processing as described in (1) of FIG. 2 is repeated.

  The control circuit 2 can detect the disconnection within the disconnection detectable period (see the period shown in FIG. 2F) from when the output OUT is set to “H” to when the output OUT is set to “L” after a predetermined time. . The control circuit 2 detects “L” when no disconnection is detected in the disconnection detectable period, and detects “H” when a disconnection is detected.

  The “predetermined time” that defines the disconnection detectable period is a disconnection undetectable period (period (2) to (3), (4) to (5) in FIG. 2) that is a period other than the disconnection detectable period. It is provided to remove The disconnection undetectable period is a period of a periodic pulse that appears as a diagnostic output when the output OUT changes transiently from “H” to “L” and from “L” to ““ H ”. Temporarily becomes “H”. The above-mentioned “predetermined time” can be ideally set except for the pulse-like disconnection undetectable period, but is preferably set in consideration of a predetermined margin period after the pulse-like disconnection undetectable period.

FIG. 3 shows a timing chart at the time of disconnection, and shows signal waveforms of main parts when the disconnection is detected.
As shown in FIG. 3B, when the load M is disconnected, the power supply is cut off from the power source Vc. Therefore, the detection voltage of the resistor R1 is constant at 0V, and as shown in FIG. The output of the detection circuit 3 is constant at “H”. As shown in FIG. 3D, the terminal voltage of the load M (the voltage of the output terminal N1) is also constant at 0V, and the output of the second voltage detection circuit 4 is “H” as shown in FIG. It becomes constant at. Therefore, as shown in FIG. 3 (f), the control circuit 2 always inputs "H" as a diagnosis output serving as a disconnection detection signal, and the control circuit 2 can detect disconnection in the disconnection detectable period. .

  According to the present embodiment, the control circuit 2 detects the disconnection based on the detection result obtained by the first voltage detection circuit 3 comparing the detection voltage of the resistor R1 with the threshold voltage ref1, and therefore the influence of unnecessary components such as noise is affected. It is hard to receive and can detect disconnection with high reliability.

  The selection circuit 5 selects either the output of the first voltage detection circuit 3 or the output of the second voltage detection circuit 4, and the control circuit 2 detects the disconnection based on the detection result selected by the selection circuit 5. Therefore, disconnection can be detected in any period when the transistor M1 is turned on / off. The period during which disconnection can be detected can be increased.

(Second Embodiment)
4 and 5 show a second embodiment of the present invention. The difference from the previous embodiment is that the current flowing through the first detection element is bypassed while the detection result of the first voltage detection circuit is not required. It is in the place where it is configured. Further, the detection result of the first voltage detection circuit is acquired by the synchronization acquisition means in synchronization with the periodic signal when the switching element is turned on, and the disconnection is detected based on the acquisition result.

  In addition, the configuration is such that the energization current of the first detection element is bypassed except for the period from when the first detection element is energized until the detection result of the first voltage detection circuit is acquired in synchronization with the periodic signal. is there. Parts having the same or similar functions as those of the above-described embodiment are denoted by the same or similar reference numerals, description thereof will be omitted as necessary, and different parts will be described below.

  FIG. 4 schematically shows the configuration of a disconnection detection circuit that replaces FIG. 1, and shows a disconnection detection circuit 11 that replaces the disconnection detection circuit 1. The disconnection detection circuit 11 includes a latch circuit 12 as a synchronization acquisition unit instead of the selection circuit 5. The latch circuit 12 is composed of, for example, a D flip-flop. An inversion signal of the output OUT is given from the output OUT to the reset terminal RST of the latch circuit 12 through the NOT gate 13. The output of the first voltage detection circuit 3 is given to the D terminal of the latch circuit 12.

  A clock signal CK (corresponding to a periodic signal) generated by the control circuit 2 is supplied to the clock input terminal of the latch circuit 12 via the switch 14. The switch 14 is a switch that can be turned on / off according to the output signal of the output OUT. For example, the switch 14 is turned on when the output OUT is “H”, and turned off when the output OUT is “L”.

  The control circuit 2 includes an oscillation circuit that oscillates the clock signal CK, for example. The clock signal CK generated by the oscillation circuit is applied to the gate of the N-channel type MOS transistor M2 through the switch 14. The drain of the transistor M2 is connected to the output terminal N2, and the source is connected to the ground. The transistor M2 functions as a bypass unit that bypasses the energization current of the resistor R1.

  As described above, when the switch 14 is turned on, the clock signal CK of the control circuit 2 is supplied to the gate of the transistor M2, and the transistor M2 bypasses the energization current flowing through the transistor M1 and the resistor R1 in synchronization with the clock signal CK. To do.

FIG. 5 shows a timing chart during normal operation (when the load is normally connected).
As shown in FIG. 5A, while the control circuit 2 outputs “H” as the output OUT, a periodic pulsed clock signal CK is output as a periodic signal as shown in FIG. 5B. . In this embodiment, as shown in FIG. 5B, the time T1 when the clock signal CK is set to “H” and the transistor M2 is turned on is set longer than the time T2 when the clock signal CK is set to “L”. Yes. That is, the first time T1 that bypasses the energization current of the resistor R1 is the time from when the resistor R1 is energized until the latch circuit 12 acquires the detection result of the first voltage detection circuit 3 in synchronization with the clock signal CK. 2 is set longer than the time T2. Then, the energization time of the current flowing through the resistor R1 can be shortened, and the power consumption can be reduced.

  As shown in FIG. 5C, the voltage of the node N1, which is the detection voltage of the first detection element, increases according to the “L” time of the clock CK and exceeds the threshold voltage ref1. As shown in FIG. 5D, when the voltage at the node N1 exceeds the threshold voltage ref1, the output of the first voltage detection circuit 3 is switched from “L” to “H”. The latch circuit 12 holds and acquires the output of the first voltage detection circuit 3 at the rising timing of the clock signal CK. The control circuit 2 acquires the output of the latch circuit 12 at the rising timing of the clock signal CK. As shown in FIG. 5G, the control circuit 2 acquires “L” as the diagnosis output, can detect that it is not disconnected, and continues to operate normally. 5 (e) and 5 (f) show the voltage at the terminal N2 of the load M and the output voltage of the second voltage detection circuit 4, respectively, but are invalid while the output OUT is “H”. Therefore, description of this operation is omitted.

  FIG. 6 shows a timing chart when disconnection is detected. As shown in FIG. 6, since the latch circuit 12 holds the output of the latch circuit 12 at the rising timing of the clock signal CK, the control circuit 2 detects the disconnection by acquiring the output of the latch circuit 12 thereafter. it can.

  FIG. 7 shows a timing chart when the switching element is disconnected while the drive output is on. As shown in FIG. 7, since the output of the first voltage detection circuit 3 is lost when the load M is disconnected, the disconnection can be detected quickly when the control circuit 2 detects the disconnection for each cycle of the clock signal CK.

  As described above, according to the present embodiment, while the detection result of the first voltage detection circuit 3 is not required, the transistor M2 bypasses the energization current of the transistor M1 and the resistor R1, and thus the current flowing through the resistor R1 is reduced. It is possible to suppress power consumption.

  The control circuit 2 acquires the detection result of the first voltage detection circuit 3 in synchronization with the clock signal CK when the transistor M1 is on, and detects disconnection based on the acquisition result. Since the disconnection can be detected for each cycle of the clock signal CK when the signal is disconnected, the disconnection can be detected quickly.

  Further, the transistor M2 bypasses the energization current of the transistor M1 and the resistor R1 except for the period from when the resistor R1 is energized until the detection result of the first voltage detection circuit 3 is acquired in synchronization with the clock signal CK. , Current consumption can be reduced.

(Third embodiment)
FIGS. 8 to 10 show a third embodiment of the present invention. The difference from the previous embodiment is that the delay acquisition means is a predetermined time after the first detection element is energized by turning on the switching element. The detection result of the first voltage detection circuit is acquired later, and the first detection element except for the time from when the bypass means energizes the first detection element until the delay acquisition means acquires the detection result of the first voltage detection circuit. It is in the place comprised so that the energization current of this may be bypassed. Hereinafter, a different part from the said embodiment is demonstrated.

  FIG. 8 shows a configuration of a disconnection detection circuit 21 that replaces the disconnection detection circuit 1. As shown in FIG. 8, the disconnection detection circuit 21 is configured by providing a delay circuit 22 in place of the switch 14. The delay circuit 22 is a circuit that delays the rising signal of the output OUT when the output OUT is input. After the delay time, the delay circuit 22 applies the rising signal of the output OUT to the clock terminal of the latch circuit 12 and the gate of the transistor M2. .

FIG. 9 schematically shows a timing chart during normal operation (when the load is normally connected).
As shown in FIG. 9B, the delay circuit 22 delays the rising signal of the output OUT by a predetermined delay time. As shown in FIG. 9D, the latch circuit 12 serving as a delay acquisition unit holds and acquires the output of the first voltage detection circuit 3 at the timing of the rising signal of the output of the delay circuit 22, ), The control circuit 2 can detect the disconnection at the timing by acquiring the hold signal. In the present embodiment, the disconnection detectable period is a period from the time when the delay circuit 22 outputs the rising signal until the output OUT becomes “L”.

  The output of the delay circuit 22 is also given to the gate of the transistor M2. For this reason, the transistor M2 bypasses the energization current of the transistor M1 and the resistor R1 except when the resistor R1 is energized until the latch circuit 12 acquires the detection result of the first voltage detection circuit 3. Thus, the current consumption can be reduced as in the above-described embodiment.

  FIG. 10 schematically shows a timing chart at the time of disconnection detection. As shown in FIG. 10, the output OUT is changed from “L” to “H” after a predetermined time. Disconnection can be detected during the period up to the point of “L”.

  According to the present embodiment, the latch circuit 12 acquires the detection result of the first voltage detection circuit 3 after a predetermined delay time from when the transistor M2 is turned on to energize the resistor R1, and the transistor M2 is connected to the resistor R1. The energization current of the resistor R1 is bypassed except for the period from when the current is energized until the latch circuit 12 acquires the detection result of the first voltage detection circuit 3. Thereby, there exists an effect similar to the above-mentioned embodiment.

(Fourth embodiment)
FIG. 11 shows a fourth embodiment of the present invention. The difference from the previous embodiment is that the first detection element is formed of a diode. Further, the threshold voltage that is the comparison target of the first voltage detection circuit is generated using the same specific diode as the diode. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

  As shown in FIG. 11, a diode D1 is provided as a first detection element instead of the resistor R1. The diode D1 is connected in series in the forward direction between the source of the transistor M1 and the ground. Since the diode D1 has a substantially constant voltage drop characteristic regardless of a current change, the diode D1 generates a substantially constant terminal voltage regardless of the load current. Therefore, the disconnection can be detected stably regardless of the characteristics of the load M. When the diode D1 is applied, the voltage applied to the diode D1 can be reduced at a predetermined current as compared with the configuration in which the resistor R1 is applied. Thereby, power consumption can be reduced and the reliability of the element can be improved.

The threshold voltage generation circuit 32 is connected to the voltage input terminal (the inverting input terminal of the comparator) to be compared with the first voltage detection circuit 3.
The threshold voltage generation circuit 32 includes a diode D2 (corresponding to the second diode) having the same characteristics as the diode D1 (corresponding to the first diode), and is formed for temperature compensation of the diode D1. . In the present embodiment, the threshold voltage generation circuit 32 applies a constant current I1 to the diode D2, and uses a voltage obtained by dividing the voltage generated at both ends of the diode D2 by the resistors R3 and R4 as a comparison target threshold voltage. Yes.

  The first voltage detection circuit 3 compares the detection voltage of the diode D1 with the threshold voltage to be compared and outputs the comparison voltage to the latch circuit 12. Even if the voltage generated in the diode D1 fluctuates due to the temperature change, the voltage generated in the diode D2 also fluctuates in the same direction according to this fluctuating current, so that the threshold voltage to be compared is also in the same direction according to the fluctuating current. Fluctuates. Therefore, the diode D2 functions as a temperature compensation element. Thereby, the temperature compensation of the diode D1 can be performed.

  It is desirable to integrate such diodes D1 and D2 in one semiconductor chip because the characteristics of the diodes D1 and D2 can be easily made the same. Although the embodiment in which one diode D1 is configured between the source of the transistor M1 and the ground is shown, a plurality of diodes D1 may be connected in series.

(Fifth embodiment)
FIG. 12 shows a fifth embodiment of the present invention. The difference from the previous embodiment is that the switching element and the bypass means are composed of MOS transistors of the same conductivity type whose drains or sources are electrically connected in common. In addition, the same conductivity type MOS transistors are formed on the same semiconductor substrate, and are formed in trench isolation. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

  In the above-described embodiment, the transistor M2 is provided in parallel with the transistor M1 and the diode D1 connected in series. However, in the configuration of this embodiment, the back gate of the transistor M2 is connected to the source. The diode D1 is configured as a body diode between the back gate and the drain of the transistor M2. Even if comprised in this way, there exists an effect similar to the above-mentioned embodiment.

  When such a configuration is integrated in a semiconductor integrated circuit, there are cases where the two transistors M1 and M2 cannot be electrically isolated, but it is easy to configure a trench isolation structure between the transistors M1 and M2. Can be integrated.

(Sixth embodiment)
FIG. 13 shows a sixth embodiment of the present invention. The difference from the previous embodiment is that the first and second voltage detection circuits are shared. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

  As shown in FIG. 13, the disconnection detection circuit 51 in place of the disconnection detection circuit 1 includes switches 52 and 53 with control terminals and a third voltage detection circuit 54. One fixed contact of the switch 52 is connected to the node N1, and the other fixed contact is connected to the node N2. The movable contact of the switch 52 is connected to the third voltage detection circuit 54. The switch 52 is configured to be able to switch the conductive connection between the plurality of fixed contacts and the movable contacts in accordance with “H” and “L” of the output OUT.

  A threshold voltage ref1 is applied to one fixed contact of the switch 53, and a threshold voltage ref2 is applied to the other fixed contact. The movable contact of the switch 53 is connected to the third voltage detection circuit 54. The third voltage detection circuit 54 compares the output of the movable contact of the switch 52 with the output of the movable contact of the switch 53 to be compared, and outputs the comparison result to the control circuit 2 as a diagnostic output.

  When the output OUT is “H”, the switch 52 switches the movable contact to the fixed contact on the node N1 side, so that the voltage of the node N1 is applied to the third voltage detection circuit 54. Further, since the switch 53 switches the movable contact to the fixed contact on the threshold voltage ref1 side, the threshold voltage ref1 is given to the third voltage detection circuit 54. The same effect as the first embodiment can be obtained.

  When the output OUT is “L”, the switch 52 switches the movable contact to the fixed contact on the node N2 side, so that the voltage of the node N2 is applied to the third voltage detection circuit 54. Further, since the switch 53 switches the movable contact to the fixed contact on the threshold voltage ref2 side, the threshold voltage ref2 is applied to the third voltage detection circuit 54. Also at this time, the same effect as the first embodiment can be obtained. That is, the switches 52 and 53 have a function as a selection circuit, and the third voltage detection circuit 54 shares the functions of the first voltage detection circuit 3 and the second voltage detection circuit 4.

  As described above, according to the present embodiment, since the third voltage detection circuit 54 shares the functions of the first voltage detection circuit 3 and the second voltage detection circuit 4 of the previous embodiment, the circuit scale is reduced. Therefore, it is possible to reduce the size and cost.

(Seventh embodiment)
FIG. 14 shows a seventh embodiment of the present invention. The difference from the previous embodiment is that it is applied to a disconnection detection circuit of a high-side drive circuit. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described below.

  In the disconnection detection circuit 61 instead of the disconnection detection circuit 1, a P-channel type MOS transistor Mp1 is provided in place of the N-channel type MOS transistor M1 of the above-described embodiment. The P-channel type MOS transistor Mp1 drives the load M on the high side and is configured symmetrically with the configuration of the previous embodiment. A NOT gate 62 is provided between the output OUT of the control circuit 2 and the selection circuit 5. Since other configurations are substantially the same, description thereof is omitted. The present embodiment can be applied to the disconnection detection circuit 61 of the high side drive circuit. In the present embodiment, an embodiment corresponding to the first embodiment of FIG. 1 is shown, but other embodiments can also be applied to the disconnection detection circuit of the high-side drive circuit.

(Eighth embodiment)
FIG. 15 and FIG. 16 show an eighth embodiment of the present invention. The difference from the previous embodiment is that a bipolar transistor, IGBT (Insulated Gate Bipolar Transistor) is applied as a switching element. As shown in FIGS. 15 and 16, an NPN bipolar transistor M3 and IGBT (M4) may be applied instead of the MOS transistor M1.

(Other embodiments)
The present invention is not limited to the above embodiment, and for example, the following modifications or expansions are possible.
The second voltage detection circuit 4 and the selection circuit 5 may be provided as necessary. For example, in the first embodiment, the control circuit 2 may be configured to detect the disconnection only when the output of the first voltage detection circuit 3 is input as a disconnection detection signal and the transistor M1 is turned on.

Although the resistor R2 is applied as the second detection element, other elements may be applied.
In the embodiment, the load M, the drain-source of the transistor M1, and the resistor R1 are connected in series between the power source Vc and the ground. However, the order of the series connection is appropriately changed as necessary. Also good.

  Both the switching elements (M1, M3, M4) and the bypass means (M2) in the above-described embodiment are composed of transistors. It is preferable that trench separation is formed on the same semiconductor substrate between these transistors (between M1-M2, between M3-M2, and between M4-M2). Then, leakage between the switching element and the bypass means can be suppressed as much as possible.

  In the embodiment to which the above-described synchronization acquisition unit is applied, in principle, the latch circuit 12 holds and acquires the output of the first voltage detection circuit 3 at the same time as the transistor M2 is turned on. In order to improve the retention and acquisition reliability, in practice, a delay circuit may be provided immediately before the path from the switch 14 of the clock signal CK to the gate of the MOS transistor M2. Then, since the latch circuit 12 holds and acquires the output of the first voltage detection circuit 3 and the transistor M2 bypasses the current, the reliability of data holding and acquisition is improved.

  In the embodiment to which the diode D1 is applied, the embodiment in which the diode D1 is connected between the source of the transistor M1 and the ground is shown. However, in addition to the diode D1, a resistor R1 is connected in series. Also good.

  In the drawings, reference numerals 1, 11, 21, 31, 41, 51 and 61 are disconnection detection circuits, 2 is a control circuit, 3 is a first voltage detection circuit, 4 is a second voltage detection circuit, and 5 and 15 are selection circuits. Is a latch circuit (delay acquisition means, synchronization acquisition means), 22 is a delay circuit, 32 is a threshold voltage generation circuit, M is a load, M1 is an N-channel MOS transistor (switching element), and M2 is an N-channel MOS transistor (Bypass means), R1 is a resistance (first detection element), R2 is a resistance (second detection element), and D1 is a diode (first detection element).

Claims (13)

A switching element that drives the load by connecting the load to the output terminal in series and turning on and off;
A first detection element that is connected in series with the switching element and generates a voltage when the switching element is energized;
A first voltage detection circuit that compares a voltage generated in the first detection element with a threshold voltage when the switching element is turned on;
A disconnection detection circuit that detects disconnection based on a detection result of the first voltage detection circuit. A second detection element connected in series to the load and connected in parallel to the switching element, and generating a voltage when the switching element is turned off;
A second voltage detection circuit for detecting a voltage generated in the second detection element by comparing with a threshold voltage;
A selection circuit for selecting a detection result of the first or second voltage detection circuit,
The disconnection detection circuit according to claim 1, wherein the disconnection is detected based on a detection result selected by the selection circuit.   3. The disconnection detection circuit according to claim 1, further comprising bypass means for bypassing an energization current of the first detection element while the detection result of the first voltage detection circuit is not required. Synchronization acquisition means for acquiring a detection result of the first voltage detection circuit in synchronization with a periodic signal when the switching element is on;
The disconnection detection circuit according to claim 1, wherein a disconnection is detected based on an acquisition result of the synchronization acquisition means. Synchronization acquisition means for acquiring the detection result of the first voltage detection circuit in synchronization with a periodic signal when the switching element is on;
Bypass the energization current of the first detection element except for the period from when the first detection element is energized until the synchronization acquisition means acquires the detection result of the first voltage detection circuit in synchronization with the periodic signal. The disconnection detection circuit according to claim 1, further comprising a bypass unit.   In the first time when the bypass means bypasses the energization current of the first detection element, the synchronization acquisition means synchronizes the detection result of the first voltage detection circuit with the periodic signal after the first detection element is energized. The disconnection detection circuit according to claim 5, wherein the disconnection detection circuit is set longer than a second time until acquisition. A delay acquisition means for acquiring a detection result of the first voltage detection circuit after a predetermined delay time from when the first detection element is energized by turning on the switching element;
Bypass means for bypassing the energization current of the first detection element except for the time from when the first detection element is energized until the delay acquisition means acquires the detection result of the first voltage detection circuit. The disconnection detection circuit according to any one of claims 1 to 3.   The disconnection detection circuit according to claim 1, wherein the first detection element includes one or more diodes. The first detection element includes one or more first diodes;
8. The disconnection according to claim 1, wherein the threshold voltage to be compared by the first voltage detection circuit is generated using a second diode having the same characteristics as the first diode. 9. Detection circuit.   10. The disconnection detection circuit according to claim 8, wherein the diode is integrated on one semiconductor chip.   11. The disconnection according to claim 1, wherein the first detection element includes one or more first diodes integrated between a back gate and a drain of a MOS transistor. Detection circuit.   The disconnection detection circuit according to claim 2, wherein the first and second voltage detection circuits are shared. The switching element and the bypass means are both constituted by MOS transistors electrically connected in common,
13. The disconnection detection circuit according to claim 5, wherein the MOS transistors are formed on the same semiconductor substrate and are formed in trench isolation.

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