Semiconductor device, light emitting device, and vehicle

Abstract

A semiconductor device 1 comprises: a switch element 11(n) connected in parallel to a light emitting element 2(n); a detection circuit 13(n) that compares the voltage V(n+1)-V(n) between both ends of the switch element 11(n) to a prescribed threshold voltage Vth and generates a detection signal S1(n); and a failure diagnosis circuit 22(n) that performs diagnosis of whether the switch element 11(n) is stuck in an OFF state by monitoring the detection signal S1(n) at a timing when the drive signal VG(n) of the switch element 11(n) is at a logic level when ON.

Description

Semiconductor device, light emitting device, vehicle

[0001] The present disclosure relates to a semiconductor device, and a light emitting device and a vehicle using the same.

[0002] A semiconductor device (e.g., a matrix switch integrated circuit (IC) or a bypass switch IC) that turns on / off a light-emitting element such as an LED (light emitting diode) element has a built-in detection circuit for detecting a failure (such as a short circuit) of the light-emitting element.

[0003] An example of the related prior art is disclosed in Japanese Patent Application Laid-Open No. 2003-222299.

[0004] Japanese Patent Application Laid-Open No. 2016-175582

[0005] However, there is room for improvement in the fault detection rate of conventional semiconductor devices.

[0006] For example, the semiconductor device disclosed in this specification includes a switch element configured to be connected in parallel to a light-emitting element, a detection circuit configured to generate a detection signal by comparing a voltage across the switch element with a predetermined threshold voltage, and a fault diagnosis circuit configured to diagnose whether the switch element is stuck off by monitoring the detection signal at a timing when a drive signal for the switch element is at an on-logic level.

[0007] Furthermore, for example, the semiconductor device disclosed in this specification includes a switch element or a current source configured to be connected in series to a light-emitting element, a detection circuit configured to generate a detection signal by comparing a voltage across the switch element or the current source with a predetermined threshold voltage, and a fault diagnosis circuit configured to diagnose whether the switch element or the current source is stuck on by monitoring the detection signal at a timing when a drive signal for the switch element or the current source is at an off logic level.

[0008] Furthermore, for example, the semiconductor device disclosed in this specification includes a switch element or a current source configured to be connected in series with a light-emitting element, a detection circuit configured to detect a drive current flowing through the switch element or the current source, and a fault diagnosis circuit configured to diagnose a stuck-on state of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an off state, and to diagnose a stuck-off state of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an on state.

[0009] Still other features, elements, steps, advantages, and characteristics will become more apparent from the detailed description that follows and the accompanying drawings related thereto.

[0010] According to the present disclosure, it is possible to provide a semiconductor device that can increase the fault detection rate, and a light emitting device and a vehicle that use the same.

[0011] FIG. 1 is a diagram illustrating a first configuration example of a light-emitting device. FIG. 2 is a diagram illustrating a first embodiment of a semiconductor device. FIG. 3 is a diagram illustrating a first example of fault diagnosis (normal). FIG. 4 is a diagram illustrating a second example of fault diagnosis (when the LED is short-circuited). FIG. 5 is a diagram illustrating a third example of fault diagnosis (when the SW is stuck on). FIG. 6 is a diagram illustrating a fourth example of fault diagnosis (when the SW is stuck off). FIG. 7 is a diagram illustrating a second configuration example of a light-emitting device. FIG. 8 is a diagram illustrating a second embodiment of a semiconductor device. FIG. 9 is a diagram illustrating a fifth example of fault diagnosis (normal). FIG. 10 is a diagram illustrating a sixth example of fault diagnosis (when the LED is short-circuited). FIG. 11 is a diagram illustrating a seventh example of fault diagnosis (when the LED is open). FIG. 12 is a diagram illustrating an eighth example of fault diagnosis (when the CS is stuck on). FIG. 13 is a diagram illustrating a ninth example of fault diagnosis (when the CS is stuck off). FIG. 14 is a diagram illustrating a third embodiment of a semiconductor device. FIG. 15 is a diagram illustrating a tenth example of fault diagnosis (normal). Fig. 16 is a diagram showing an eleventh example of fault diagnosis (when CS is stuck on). Fig. 17 is a diagram showing a twelfth example of fault diagnosis (when CS is stuck off). Fig. 18 is a diagram showing the exterior (front) of a vehicle in which a light-emitting device can be installed. Fig. 19 is a diagram showing the exterior (rear) of a vehicle in which a light-emitting device can be installed.

[0012] <Light-emitting device (first configuration example)> Fig. 1 is a diagram showing a first configuration example of a light-emitting device. The light-emitting device 100 of this configuration example includes a semiconductor device 1 and light-emitting elements 2(0) to 2(7). The light-emitting device 100 may be, for example, a headlamp, tail lamp, stop lamp, turn lamp, or interior lamp (such as an instrument panel lamp) of a vehicle.

[0013] The semiconductor device 1 is a matrix switch IC (bypass switch IC) that switches between short-circuiting and non-shorting each of the light-emitting elements 2(0) to 2(7). The semiconductor device 1 is equipped with a plurality of external terminals (external terminals CH(0) to CH(8) in this figure) as means for establishing electrical connection with the outside of the device.

[0014] The light-emitting elements 2(0) to 2(7) are each a series light-emitting element provided on a current path through which a drive current ILED flows. When the light-emitting elements 2(0) to 2(7) are viewed individually, each can be understood as a single LED element, or as a light-emitting element assembly in which multiple LED elements are combined in series or in parallel.

[0015] The cathode of the light-emitting element 2(n) (where n = 0, 1, ..., 7, and so forth) is connected to the external terminal CH(n) of the semiconductor device 1. On the other hand, the anode of the light-emitting element 2(n) is connected to the external terminal CH(n+1) of the semiconductor device 1.

[0016] Although not explicitly shown in the figure, the light emitting device 100 may also include a semiconductor device (a so-called LED driver IC) that generates the above-mentioned drive current ILED.

[0017] <Semiconductor Device> The internal configuration of the semiconductor device 1 will now be described with reference to Fig. 1. The semiconductor device 1 of this configuration example includes a built-in switch circuit 10 and a control circuit 20.

[0018] The switch circuit 10 includes switch elements 11(0) to 11(7) (N-channel type metal oxide semiconductor field effect transistors [NMOSFETs] in this figure), drivers 12(0) to 12(7), detection circuits 13(0) to 13(7), and level shifters 14(0) to 14(7). The control circuit 20 also includes PWM [pulse width modulation] dimming circuits 21(0) to 21(7).

[0019] The switch element 11(n) is connected in parallel to the light-emitting element 2(n). Specifically, with reference to this figure, the source of the switch element 11(n) is connected to the external terminal CH(n). The drain of the switch element 11(n) is connected to the external terminal CH(n+1). The gate of the switch element 11(n) is connected to the application terminal of the drive signal VG(n) (= the output terminal of the driver 12(n)).

[0020] The switch element 11(n) connected in this manner is in an on state when the drive signal VG(n) is at a high level, and in an off state when the drive signal VG(n) is at a low level. When the switch element 11(n) is in an on state, both ends of the light-emitting element 2(n) are short-circuited. Therefore, the light-emitting element 2(n) is in an extinguished state (=unlightable state). On the other hand, when the switch element 11(n) is in an off state, both ends of the light-emitting element 2(n) are not short-circuited. Therefore, the light-emitting element 2(n) is in an lit state (=lightable state).

[0021] The driver 12(n) generates the drive signal VG(n) in response to the control signal S4(n) output from the PWM dimming circuit 21(n) (more precisely, the level-shifted control signal S5(n) output from the level shifter 14(n)). For example, the driver 12(n) sets the drive signal VG(n) to a high level when the control signal S4(n) is at a high level, and sets the drive signal VG(n) to a low level when the control signal S4(n) is at a low level.

[0022] The driver 12(n) also has a function of forcibly fixing the logic level of the drive signal VG(n) in response to the detection signal S2(n) output from the detection circuit 13(n).

[0023] The detection circuit 13(n) monitors the voltage across the switch element 11(n) and generates detection signals S1(n) and S2(n). The voltage across the switch element 11(n) is detected as a differential voltage V(n+1)-V(n) between the node voltage V(n) appearing at the external terminal CH(n) and the node voltage V(n+1) appearing at the external terminal CH(n+1). Note that the detection signals S1(n) and S2(n) may be the same signal.

[0024] The level shifter 14(n) is provided between the control circuit 20 and the driver 12(n) and detection circuit 13(n). The level shifter 14(n) generates a level-shifted control signal S5(n) by shifting the signal level of the control signal S4(n) output from the PWM dimming circuit 21(n). The level shifter 14(n) then outputs the level-shifted control signal S5(n) to the driver 12(n). The level shifter 14(n) also shifts the signal level of the detection signal S1(n) output from the detection circuit 13(n) to generate a level-shifted detection signal S3(n). The level shifter 14(n) then outputs the level-shifted detection signal S3(n) to the control circuit 20.

[0025] The PWM dimming circuit 21(n) generates a control signal S4(n) with an on-duty Don (= the ratio of the on-period to the pulse period) corresponding to the luminance of the light-emitting element 2(n). As previously mentioned, the light-emitting element 2(n) is in an off state (= an unlightable state) when the switch element 11(n) is in an on state, and in an on state (= an light-enabled state) when the switch element 11(n) is in an off state. Therefore, when the light-emitting element 2(n) is to be fully lit (100% luminance), the on-duty Don of the control signal S4(n) is set to 0% (always low level). On the other hand, when the light-emitting element 2(n) is to be turned off, the on-duty Don of the control signal S4(n) is set to 100% (always high level).

[0026] <Considerations on Fault Detection Rate> Incidentally, when the semiconductor device 1 is used for in-vehicle applications, it must satisfy strict international standards related to functional safety. For example, in order to comply with one of the international standards, ISO (International Organization for Standardization) 26262, failure analysis of the semiconductor device 1 by failure modes, effects and diagnostics analysis (also known as FMEDA) is required.

[0027] To achieve this, it is necessary not only to perform fault detection (LED short circuit detection) of the light-emitting element 2(n) externally attached to the semiconductor device 1, but also to increase the fault detection rate of the internal elements and internal circuits built into the semiconductor device 1, depending on the safety level required by the system.

[0028] The fault detection rate of the semiconductor device 1 is calculated proportionally to the element area. Therefore, for example, if a fault in the switch element 11(n) having a large element area cannot be detected, a single point fault occurs, and the fault detection rate of the semiconductor device 1 drops significantly.

[0029] In the following, in view of the above considerations, a novel embodiment capable of increasing the fault detection rate of the semiconductor device 1 will be proposed.

[0030] 2 is a diagram showing a first embodiment (particularly, a group of components related to fault diagnosis) of the semiconductor device 1. In the semiconductor device 1 of this embodiment, a hysteresis comparator is used as the aforementioned detection circuit 13(n).

[0031] Referring to the figure, the non-inverting input terminal (+) of detection circuit 13(n) receives an added voltage V(n)+Vth(n) obtained by adding the node voltage V(n) appearing at external terminal CH(n) and the threshold voltage Vth(n). Meanwhile, the inverting input terminal (-) of detection circuit 13(n) receives the node voltage V(n+1) appearing at external terminal CH(n+1).

[0032] Therefore, the detection signal S1(n) is at a low level when V(n+1)>V(n)+Vth(n) and at a high level when V(n+1)>V(n)+Vth(n). In other words, the detection signal S1(n) is at a low level when V(n+1)-V(n)>Vth(n) and at a high level when V(n+1)-V(n)<Vth(n).

[0033] As described above, the detection circuit 13(n) generates the detection signal S1(n) by comparing the voltage V(n+1)-V(n) across the switch element 11(n) with a predetermined threshold voltage Vth(n). The threshold voltage Vth(n) is set to a voltage value lower than the forward drop voltage Vf of the light-emitting element 2(n), for example.

[0034] In the semiconductor device 1 of this embodiment, the control circuit 20 further includes a fault diagnosis circuit 22(n).

[0035] The fault diagnosis circuit 22(n) monitors the detection signal S1(n) at the timing when the drive signal VG(n) of the switch element 11(n) is at a low level (=logical level when off), thereby diagnosing whether the switch element 11(n) is stuck on or whether the light-emitting element 2(n) to which the switch element 11(n) is connected in parallel is short-circuited.

[0036] The switch element 11(n) being stuck on (hereinafter sometimes referred to as "SW stuck on") refers to a failure mode in which the switch element 11(n) does not turn off and remains in the on state even though the drive signal VG(n) for the switch element 11(n) is set to a low level (= the logical level when off).

[0037] Furthermore, the fault diagnosis circuit 22(n) performs a stuck-off diagnosis of the switch element 11(n) by monitoring the detection signal S1(n) at the timing when the drive signal VG(n) of the switch element 11(n) is at a high level (= the logic level when on).

[0038] The switch element 11(n) being stuck off (hereinafter sometimes referred to as "SW stuck off") refers to a failure mode in which the switch element 11(n) does not turn on but remains in the off state even though the drive signal VG(n) for the switch element 11(n) is set to a high level (= the logical level when on).

[0039] 3 is a diagram showing a first example of fault diagnosis (normal operation in the first embodiment). From top to bottom, the diagram depicts the drive signal VG(n), the on / off state of the switch element 11(n), the on / off state of the light-emitting element 2(n), the voltage V(n+1)-V(n) across the switch element 11(n), and the detection signal S1(n).

[0040] Under normal conditions where neither the light-emitting element 2(n) nor the switch element 11(n) has a failure, when the drive signal VG(n) is at a high level, the switch element 11(n) is in an on state. At this time, the light-emitting element 2(n) is bypassed by the switch element 11(n), and therefore the drive current ILED does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an off state (=unable to light). Furthermore, when the switch element 11(n) is in an on state, the voltage V(n+1)-V(n) across the switch element 11(n) is 0 V (<Vth(n)). Therefore, the detection signal S1(n) is at a high level.

[0041] Furthermore, when the light-emitting element 2(n) and the switch element 11(n) are operating normally, if the drive signal VG(n) is at a low level, the switch element 11(n) is in an off state. At this time, the bypass of the light-emitting element 2(n) by the switch element 11(n) is released, and the drive current ILED flows through the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an illuminating state (= an illuminatable state). Furthermore, when the switch element 11(n) is in an off state, the voltage V(n+1)-V(n) across the switch element 11(n) is equal to the forward drop voltage Vf (>Vth(n)) of the light-emitting element 2(n). Therefore, the detection signal S1(n) is at a low level.

[0042] In view of the behavior in FIG. 3, if the detection signal S1(n) is at a high level when the drive signal VG(n) is at a high level, and if the detection signal S1(n) is at a low level when the drive signal VG(n) is at a low level, the fault diagnosis circuit 22(n) diagnoses that both the light-emitting element 2(n) and the switch element 11(n) are normal.

[0043] 4 is a diagram showing a second example of fault diagnosis (when an LED is short-circuited in the first embodiment). In this diagram, similar to the above-mentioned FIG. 3, from top to bottom, the drive signal VG(n), the on / off state of the switch element 11(n), the on / off state of the light-emitting element 2(n), the voltage V(n+1)-V(n) across the switch element 11(n), and the detection signal S1(n) are depicted.

[0044] When the anode and cathode of light-emitting element 2(n) are short-circuited, drive signal VG(n) is set to low level, and even if switch element 11(n) is turned off, drive current ILED does not flow to light-emitting element 2(n). Therefore, light-emitting element 2(n) is in an extinguished state (=unilluminable state). Furthermore, since no forward drop voltage Vf occurs across light-emitting element 2(n), the voltage V(n+1)-V(n) across switch element 11(n) becomes lower than threshold voltage Vth(n). Therefore, detection signal S1(n) becomes high level.

[0045] 5 is a diagram showing a third example of fault diagnosis (when SW is stuck on in the first embodiment). As with the previously described FIGS. 3 and 4, this diagram depicts, from top to bottom, drive signal VG(n), the on / off state of switch element 11(n), the on / off state of light-emitting element 2(n), the voltage V(n+1)-V(n) across switch element 11(n), and detection signal S1(n).

[0046] When the switch element 11(n) is fixed on, even if the drive signal VG(n) is set to low level, the switch element 11(n) does not turn off but remains on. As a result, the light-emitting element 2(n) is bypassed by the switch element 11(n), and the drive current ILED does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an extinguished state (=unilluminable state). Furthermore, when the switch element 11(n) is in an on state, the voltage V(n+1)-V(n) across the switch element 11(n) is 0 V (<Vth(n)). Therefore, the detection signal S1(n) becomes high level.

[0047] In consideration of the behaviors shown in FIGS. 4 and 5, when the detection signal S1(n) is at a high level while the drive signal VG(n) is at a low level, the fault diagnosis circuit 22(n) diagnoses that a short circuit has occurred in the light-emitting element 2(n) (FIG. 4) or that the switch element 11(n) is stuck on (FIG. 5).

[0048] 6 is a diagram showing a fourth example of fault diagnosis (when the SW is stuck off in the first embodiment). As with the previous FIGS. 3 to 5, this diagram depicts, from top to bottom, the drive signal VG(n), the on / off state of the switch element 11(n), the on / off state of the light-emitting element 2(n), the voltage V(n+1)-V(n) across the switch element 11(n), and the detection signal S1(n).

[0049] When the switch element 11(n) is fixed off, even if the drive signal VG(n) is set to high level, the switch element 11(n) does not turn on but remains in the off state. As a result, the light-emitting element 2(n) is not bypassed, and the drive current ILED flows to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the on state (=unlight-off state). Furthermore, when the switch element 11(n) is in the off state, the voltage V(n+1)-V(n) across the switch element 11(n) becomes the forward drop voltage Vf (>Vth(n)) of the light-emitting element 2(n). Therefore, the detection signal S1(n) becomes low level.

[0050] In view of the behavior shown in FIG. 6, the fault diagnosis circuit 22(n) diagnoses that the switch element 11(n) is stuck off when the detection signal S1(n) is at a low level during a period in which the drive signal VG(n) is at a high level.

[0051] In this way, the fault diagnosis circuit 22(n) can diagnose not only the short circuit of the light emitting element 2(n) but also the stuck-on state and stuck-off state of the switch element 11(n).

[0052] As mentioned above, the fault detection rate of the semiconductor device 1 is calculated proportionally based on the element area. Therefore, if a fault in the switch element 11(n) having a large element area can be detected, the fault detection rate of the semiconductor device 1 will be significantly improved.

[0053] Furthermore, the detection circuit 13(n) can be a conventional LED short detection circuit, so the circuit size of the semiconductor device 1 does not become unnecessarily large.

[0054] Fault diagnosis circuit 22(n) may output the fault diagnosis result to the outside of semiconductor device 1. For example, the fault diagnosis result may be a flag output, or may be read out as register data.

[0055] With this configuration, a host (e.g., an ECU [electronic control unit]) that receives a failure diagnosis result from the semiconductor device 1 can transition the light emitting device 100 to a safe state in accordance with the failure diagnosis result. Note that, as a method for realizing functional safety of the light emitting device 100, for example, it is conceivable to notify the driver of the occurrence of a failure by stopping the drive current ILED and turning off all of the light emitting elements 2(0) to 2(7).

[0056] Furthermore, the fault diagnosis circuit 22(n) may transition the semiconductor device 1 to a safe state by itself in accordance with the fault diagnosis result without waiting for control from the host. Note that, as a method for realizing the functional safety of the semiconductor device 1, for example, it is conceivable to notify the driver of the occurrence of a fault by turning all the switch elements 11(0) to 11(7) on and off in a manner different from normal (all on, all off, blinking, sequential lighting, etc.).

[0057] <Light-emitting device (second configuration example)> Fig. 7 is a diagram showing a second configuration example of a light-emitting device. The light-emitting device 100 of this configuration example includes a semiconductor device 1 and light-emitting elements 2(0) to 2(7). The cathode of light-emitting element 2(n) is connected to an external terminal CH(n) of the semiconductor device 1. On the other hand, the anodes of light-emitting element 2(n) are all connected to a power supply circuit (not shown). In other words, light-emitting elements 2(0) to 2(7) are connected in parallel to a power supply circuit (not shown).

[0058] The semiconductor device 1 includes a switch circuit 10 and a control circuit 20. The switch circuit 10 includes current sources 15(0) to 15(7) and detection circuits 16(0) to 16(7).

[0059] The current source 15(n) is connected in series to the light-emitting element 2(n). Referring to the figure, the current source 15(n) is connected between the external terminal CH(n) and the ground terminal. The current source 15(n) may be replaced with a switch element.

[0060] The current source 15(n) connected in this manner is controlled to be on / off in accordance with the drive signal S12(n) output from the PWM dimming circuit 21(n) of the control circuit 20. When the current source 15(n) is in the on state, the drive current ILED(n) flows to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the on state. On the other hand, when the current source 15(n) is in the off state, the drive current ILED(n) does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the off state.

[0061] The detection circuit 16(n) monitors the voltage across the current source 15(n) (= the node voltage VC(n) applied to the external terminal CH(n)) and generates a detection signal S11(n). Note that the node voltage VC(n) can be understood as the cathode voltage of the light-emitting element 2(n).

[0062] The node voltages VC(0) to VC(7) may be output feedback controlled so that the lowest voltage among them coincides with a predetermined reference voltage Vfb.

[0063] <Semiconductor Device (Second Embodiment)> FIG. 8 is a diagram showing a second embodiment of the semiconductor device 1 (particularly an example of the detection circuit 16(n) used in the light emitting device 100 of the second configuration example ( FIG. 7 )). In the semiconductor device 1 of this embodiment, the detection circuit 16(n) includes comparators 16a(n) and 16b(n). The detection circuit 16(n) outputs detection signals S11a(n) and S11b(n) as the aforementioned detection signal S11(n).

[0064] The comparator 16a(n) compares the node voltage VC(n) input to the non-inverting input terminal (+) with the threshold voltage Vth1 input to the inverting input terminal (-) to output a detection signal S11a(n). Therefore, the detection signal S11a(n) becomes high level when VC(n) > Vth1, and becomes low level when VC(n) < Vth1. The threshold voltage Vth1 corresponds to the short-circuit detection voltage of the light-emitting element 2(n). The threshold voltage Vth1 is set to a voltage value higher than the reference voltage Vfb.

[0065] The comparator 16b(n) compares the node voltage VC(n) input to the inverting input terminal (-) with the threshold voltage Vth2 input to the non-inverting input terminal (+) to output a detection signal S11b(n). Therefore, the detection signal S11b(n) becomes low level when VC(n) > Vth2, and becomes high level when VC(n) < Vth2. The threshold voltage Vth2 corresponds to the open detection voltage of the light-emitting element 2(n). The threshold voltage Vth2 is set to a voltage value lower than the reference voltage Vfb.

[0066] The fault diagnosis circuit 22(n) monitors the detection signals S11a(n) and S11b(n) at the timing when the drive signal S12(n) of the current source 15(n) is at the on-logic level, and performs a short circuit diagnosis and an open circuit diagnosis of the light-emitting element 2(n).

[0067] Furthermore, the fault diagnosis circuit 22(n) monitors at least one of the detection signals S11a(n) and S11b(n) at the timing when the drive signal S12(n) of the current source 15(n) is at the off-state logical level, and performs a stuck-on diagnosis or a stuck-off diagnosis of the current source 15(n).

[0068] The term "current source 15(n) stuck on" (hereinafter sometimes referred to as "CS stuck on") refers to a failure mode in which the current source 15(n) does not turn off and remains on even though the drive signal S12(n) of the current source 15(n) is at the logic level for off.

[0069] The stuck-off state of the current source 15(n) (hereinafter sometimes referred to as "CS stuck-off state") refers to a failure mode in which the current source 15(n) does not turn on and remains in the off state even though the drive signal S12(n) of the current source 15(n) is set to the logic level for the on state.

[0070] 9 is a diagram showing a fifth example of fault diagnosis (normal operation in the second embodiment). From the top, the diagram depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the node voltage VC(n), and the detection signals S11a(n) and S11b(n).

[0071] Under normal conditions where neither the light-emitting element 2(n) nor the current source 15(n) has a fault, when the drive signal S12(n) of the current source 15(n) is at the on logic level, the current source 15(n) is in the on state. At this time, the drive current ILED flows through the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the lit state. Furthermore, when the current source 15(n) is in the on state, the node voltage VC(n) is equal to or close to the reference voltage Vfb. That is, Vth2<VC(n)<Vth1 holds. Therefore, the detection signals S11a(n) and S11b(n) are both at the low level.

[0072] Furthermore, when the light-emitting element 2(n) and current source 15(n) are operating normally, if the drive signal S12(n) of the current source 15(n) is at the off logic level, the current source 15(n) is in the off state. At this time, no drive current ILED flows through the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the extinguished state. Furthermore, when the current source 15(n) is in the off state, the node voltage VC(n) is higher than the threshold voltage Vth1. In other words, Vth2<Vth1<VC(n) holds. Therefore, the detection signal S11a(n) is at a high level, and the detection signal S11b(n) is at a low level.

[0073] In view of the behavior of FIG. 9 , the fault diagnosis circuit 22(n) diagnoses that both the light-emitting element 2(n) and the current source 15(n) are normal when the detection signals S11a(n) and S11b(n) are both at a low level when the drive signal S12(n) is at an on-logic level, and when the detection signal S11a(n) is at a high level and the detection signal S11b(n) is at a low level when the drive signal S12(n) is at an off-logic level.

[0074] 10 is a diagram showing a sixth example of fault diagnosis (when an LED is short-circuited in the second embodiment). Note that, like FIG. 9, this diagram depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the node voltage VC(n), and the detection signals S11a(n) and S11b(n).

[0075] When the anode and cathode of light-emitting element 2(n) are short-circuited, even if drive signal S12(n) is set to the on-logic level and current source 15(n) is turned on, drive current ILED does not flow through light-emitting element 2(n). Therefore, light-emitting element 2(n) is turned off (i.e., unable to be turned on). Furthermore, since no forward voltage drop Vf occurs across light-emitting element 2(n), node voltage VC(n) becomes higher than threshold voltage Vth1. In other words, Vth2<Vth1<VC(n) holds. Therefore, detection signal S11a(n) goes high, and detection signal S11b(n) goes low.

[0076] In view of the behavior shown in FIG. 10, when the detection signal S11a(n) is at a high level at the timing when the drive signal S12(n) is at an on-logic level, the fault diagnosis circuit 22(n) diagnoses that a short circuit has occurred in the light-emitting element 2(n).

[0077] 11 is a diagram showing a seventh example of fault diagnosis (when an LED is open in the second embodiment). Note that this diagram, like the previously described FIGS. 9 and 10, depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the node voltage VC(n), and the detection signals S11a(n) and S11b(n).

[0078] When the external terminal CH(n) is in an open state, even if the drive signal S12(n) is set to the on logic level and the current source 15(n) is in the on state, the drive current ILED does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an extinguished state (=unilluminable state). Furthermore, the node voltage VC(n) becomes lower than the threshold voltage Vth2. In other words, VC(n) < Vth2 < Vth1 holds. Therefore, the detection signal S11a(n) becomes low level, and the detection signal S11b(n) becomes high level.

[0079] In view of the behavior shown in FIG. 11, when the detection signal S11b(n) is at a high level at the timing when the drive signal S12(n) is at an on-logic level, the fault diagnosis circuit 22(n) diagnoses that an open circuit has occurred in the light-emitting element 2(n).

[0080] 12 is a diagram showing an eighth example of fault diagnosis (when CS is stuck on in the second embodiment). Note that, like the above-mentioned FIGS. 9 to 11, this diagram depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the node voltage VC(n), and the detection signals S11a(n) and S11b(n).

[0081] When the current source 15(n) is fixed on, even if the drive signal S12(n) is set to the off logic level, the current source 15(n) does not turn off but remains on. As a result, the drive current ILED continues to flow through the light-emitting element 2(n). This causes the light-emitting element 2(n) to be in a lit state (i.e., unable to be turned off). Furthermore, when the current source 15(n) is in an on state, the node voltage VC(n) is equal to or close to the reference voltage Vfb. In other words, Vth2<VC(n)<Vth1 holds. Therefore, the detection signals S11a(n) and S11b(n) are both low.

[0082] In view of the behavior shown in FIG. 12, the fault diagnosis circuit 22(n) diagnoses that the current source 15(n) is stuck on when the detection signal S11a(n) is at a low level at the timing when the drive signal S12(n) is at an off logical level.

[0083] 13 is a diagram showing a ninth example of fault diagnosis (when CS is stuck off in the second embodiment). Note that, like the previously described FIGS. 9 to 12, this diagram depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the node voltage VC(n), and the detection signals S11a(n) and S11b(n).

[0084] When the current source 15(n) is fixed off, even if the drive signal S12(n) is set to the logic level for on, the current source 15(n) does not turn on and remains in the off state. As a result, the drive current ILED does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an off state (=unlightable state). Furthermore, since no forward drop voltage Vf occurs in the light-emitting element 2(n), the node voltage VC(n) becomes higher than the threshold voltage Vth1. In other words, Vth2<Vth1<VC(n) holds. Therefore, the detection signal S11a(n) becomes high level and the detection signal S11b(n) becomes low level.

[0085] Note that there is no difference between the behavior when current source 15(n) is stuck off (this figure) and the behavior when light-emitting element 2(n) is short-circuited ( FIG. 10 ). Therefore, when detection signal S11a(n) is at a high level at the timing when drive signal S12(n) is at the on-logic level, fault diagnosis circuit 22(n) diagnoses that light-emitting element 2(n) is short-circuited ( FIG. 10 ) or current source 15(n) is stuck off ( FIG. 13 ).

[0086] <Semiconductor device (third embodiment)> Figure 14 is a diagram showing a third embodiment of the semiconductor device 1 (particularly a specific example of the current source 15(n) and a modified example of the detection circuit 16(n) used in the light-emitting device 100 of the second configuration example (Figure 7)).

[0087] In the semiconductor device 1 of this embodiment, the current source 15(n) includes a transistor 15a(n) (an NMOSFET in this example), a resistor 15b(n), and an amplifier 15c(n). The detection circuit 16(n) includes a comparator 16c(n). The detection circuit 16(n) outputs a detection signal S11c(n) as the aforementioned detection signal S11(n).

[0088] The drain of the transistor 15a(n) is connected to the external terminal CH(n). The source of the transistor 15a(n) is connected to a first terminal of the resistor 15b(n). The second terminal of the resistor 15b(n) is connected to the ground terminal.

[0089] The resistor 15b(n) connected in this manner functions as a current / voltage conversion element that generates a sense voltage Vs(n) (= ILED(n) × Rs, where Rs is the resistance value of the resistor 15b(n)) corresponding to the drive current ILED(n).

[0090] The amplifier 15c(n) controls the gate of the transistor 15a(n) so that a predetermined reference voltage Vref input to the non-inverting input terminal (+) matches the sense voltage Vs(n) input to the inverting input terminal (-). Therefore, the drive current ILED has a voltage value (=Vref / Rs) corresponding to the reference voltage Vref. Note that the reference voltage Vref may be adjustable using a digital-to-analog converter (DAC) or the like.

[0091] The comparator 16c(n) compares the sense voltage Vs(n) input to its inverting input terminal (-) with a threshold voltage Vth3 input to its non-inverting input terminal (+) to output a detection signal S11c(n). Therefore, the detection signal S11c(n) is at a low level when Vs(n) > Vth3, and at a high level when Vs(n) < Vth3. The threshold voltage Vth3 is set to a voltage value lower than the reference voltage Vref (for example, Vth3 = Vref x n, where 0 < n < 1).

[0092] The fault diagnosis circuit 22(n) performs a stuck-on diagnosis or a stuck-off diagnosis of the current source 15(n) by monitoring the detection signal S11c(n) both when the drive signal S12(n) of the current source 15(n) is at the off-logic level and when the drive signal S12(n) of the current source 15(n) is at the on-logic level.

[0093] 15 is a diagram showing a tenth example of fault diagnosis (normal operation in the third embodiment). From the top, the diagram depicts the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the sense voltage Vs(n), and the detection signal S11c(n).

[0094] Under normal conditions where neither the light-emitting element 2(n) nor the current source 15(n) has a fault, when the drive signal S12(n) of the current source 15(n) is at an on logic level, the current source 15(n) is in an on state. At this time, a drive current ILED flows through the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an illuminated state. Furthermore, when the drive current ILED flows, the sense voltage Vs(n) becomes higher than the threshold voltage Vth3. Therefore, the detection signal S11c(n) becomes low level.

[0095] Furthermore, when the light-emitting element 2(n) and current source 15(n) are operating normally, if the drive signal S12(n) of the current source 15(n) is at the off logic level, the current source 15(n) is in the off state. At this time, no drive current ILED flows through the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in the off state. Furthermore, when no drive current ILED flows, the sense voltage Vs(n) becomes lower than the threshold voltage Vth3. Therefore, the detection signal S11c(n) becomes high level.

[0096] In view of the behavior of FIG. 15 , when the detection signal S11c(n) is at a low level when the drive signal S12(n) is at an on-logic level and when the detection signal S11c(n) is at a high level when the drive signal S12(n) is at an off-logic level, the fault diagnosis circuit 22(n) diagnoses that both the light-emitting element 2(n) and the current source 15(n) are normal.

[0097] 16 is a diagram showing an eleventh example of fault diagnosis (when CS is stuck on in the third embodiment). As with the above-mentioned FIG. 15, this diagram depicts, from top to bottom, the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the sense voltage Vs(n), and the detection signal S11c(n).

[0098] When the current source 15(n) is fixed on, even if the drive signal S12(n) is set to the off logic level, the current source 15(n) does not turn off but remains on. As a result, the drive current ILED continues to flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in a light-on state (=unlight-off state). Furthermore, when the drive current ILED flows, the sense voltage Vs(n) becomes higher than the threshold voltage Vth3. Therefore, the detection signal S11c(n) becomes low level.

[0099] In consideration of the behavior shown in FIG. 16, the fault diagnosis circuit 22(n) diagnoses that the current source 15(n) is stuck on when the detection signal S11c(n) is at a low level at the timing when the drive signal S12(n) is at an off logical level.

[0100] 17 is a diagram showing a twelfth example of fault diagnosis (when CS is stuck off in the third embodiment). As with the previously described Figs. 15 and 16, this diagram depicts, from top to bottom, the drive signal S12(n) of the current source 15(n), the on / off state of the light-emitting element 2(n), the sense voltage Vs(n), and the detection signal S11c(n).

[0101] When the current source 15(n) is fixed off, even if the drive signal S12(n) is set to the logic level for on, the current source 15(n) does not turn on and remains in the off state. As a result, the drive current ILED does not flow to the light-emitting element 2(n). Therefore, the light-emitting element 2(n) is in an off state (=unable to light up). Furthermore, when the drive current ILED does not flow, the sense voltage Vs(n) becomes lower than the threshold voltage Vth3. Therefore, the detection signal S11c(n) becomes high level.

[0102] In view of the behavior shown in FIG. 17, the fault diagnosis circuit 22(n) diagnoses that the current source 15(n) is stuck off when the detection signal S11c(n) is at a high level at the timing when the drive signal S12(n) is at the on logical level.

[0103] The second embodiment (FIG. 8) and the third embodiment (FIG. 14) may be combined. By combining the two detection methods, it becomes possible to correctly diagnose the failure mode of each of the light-emitting element 2(n) and the current source 15(n).

[0104] 18 and 19 are diagrams showing the exterior (front and rear) of a vehicle on which the above-described light-emitting device 100 can be mounted. The light-emitting device 100 can be suitably used, for example, as a headlamp (including high beam / low beam / low beam / fog lamp, etc., as appropriate) X11, a daytime running lamp (DRL) X12, a tail lamp (including low beam / low beam / fog lamp, etc., as appropriate) X13, a stop lamp X14, and a turn lamp X15 of the vehicle X10. Although not explicitly shown in the drawings, the light-emitting device 100 may also be an interior lamp (such as an instrument panel lamp) of the vehicle X10.

[0105] <Summary> The various embodiments described above will be summarized below.

[0106] For example, the semiconductor device disclosed in this specification has a configuration (first configuration) including a switch element configured to be connected in parallel to a light-emitting element, a detection circuit configured to generate a detection signal by comparing a voltage across the switch element with a predetermined threshold voltage, and a fault diagnosis circuit configured to diagnose whether the switch element is stuck off by monitoring the detection signal at a timing when a drive signal for the switch element is at an on-logic level.

[0107] In the semiconductor device according to the first configuration, the fault diagnosis circuit may be configured (second configuration) to diagnose whether the switch element is stuck on or whether the light-emitting element to which the switch element is connected in parallel is short-circuited by monitoring the detection signal at a timing when the drive signal is at an off logic level.

[0108] In the semiconductor device according to the first or second configuration, the fault diagnosis circuit may be configured to output a fault diagnosis result to an external device of the semiconductor device (third configuration).

[0109] In the semiconductor device according to any one of the first to third configurations, the fault diagnosis circuit may be configured to transition the semiconductor device to a safe state (fourth configuration).

[0110] The semiconductor device according to any one of the first to fourth configurations may be configured (fifth configuration) further including a control circuit configured to generate a control signal, and a driver configured to generate the drive signal in response to the control signal.

[0111] The semiconductor device according to the fifth configuration may be configured (sixth configuration) further including a level shifter configured to shift the signal level of the control signal between the control circuit and the driver.

[0112] Furthermore, for example, the semiconductor device disclosed in this specification is configured (seventh configuration) to include a switch element or a current source configured to be connected in series to a light-emitting element, a detection circuit configured to generate a detection signal by comparing a voltage across the switch element or the current source with a predetermined threshold voltage, and a fault diagnosis circuit configured to diagnose whether the switch element or the current source is stuck on by monitoring the detection signal at a timing when a drive signal for the switch element or the current source is at an off logic level.

[0113] In the semiconductor device according to the seventh configuration, the fault diagnosis circuit may be configured (eighth configuration) to perform a stuck-off diagnosis of the switch element or the current source, or a short-circuit or open-circuit diagnosis of the light-emitting element by monitoring the detection signal at the timing when the drive signal is at the on-logic level.

[0114] Furthermore, for example, the semiconductor device disclosed in this specification is configured (ninth configuration) to include: a switch element or a current source configured to be connected in series to a light-emitting element; a detection circuit configured to detect a drive current flowing through the switch element or the current source and generate a detection signal; and a fault diagnosis circuit configured to diagnose a stuck-on state of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an off state, and to diagnose a stuck-off state of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an on state.

[0115] Furthermore, for example, the light-emitting device disclosed in this specification has a configuration (tenth configuration) that includes the light-emitting element and a semiconductor device having any one of the first to ninth configurations described above.

[0116] The light emitting device according to the tenth configuration may be configured (eleventh configuration) in which the light emitting element is an LED element or an organic EL element.

[0117] Furthermore, for example, the vehicle disclosed in this specification is configured (twelfth configuration) to include the light-emitting device according to the tenth or eleventh configuration.

[0118] <Other Modifications> In addition to the above-described embodiments, the various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation.

[0119] For example, in the above embodiment, an example configuration using LED elements as light-emitting elements has been described, but the configuration of the present disclosure is not limited to this, and it is also possible to use, for example, organic EL (electroluminescence) elements as light-emitting elements.

[0120] As such, the above-described embodiments should be considered to be illustrative and not restrictive in all respects. The technical scope of the present disclosure is defined by the claims, and it should be understood that all modifications within the meaning and scope of the claims are included.

[0121] 1 Semiconductor device 2, 2 (0) to 2 (7), 2 (n) Light-emitting element 10 Switch circuit 11, 11 (0) to 11 (7), 11 (n) Switch element (NMOSFET) 12 (0) to 12 (7) Driver 13, 13 (0) to 13 (7), 13 (n) Detection circuit 14 (0) to 14 (7) Level shifter 15 (0) to 15 (7) Current source 15 a (n) Transistor (NMOSFET) 15 b (n) Resistor 15 c (n) Amplifier 16 (0) to 16 (7) Detection circuit 16 a (n), 16 b (n) Comparator 16 c (n) Comparator 20 Control circuit 21 (0) to 21 (7) PWM dimming circuit 22, 22 (n) Fault diagnosis circuit 100 Light-emitting device CH(0) to CH(8), CH(n), CH(n+1) External terminal X10 Vehicle X11 Headlamp X12 Daytime running lamp X13 Tail lamp X14 Stop lamp X15 Turn lamp

Claims

1. A switch element configured to be connected in parallel to the light emitting element; a detection circuit configured to compare a voltage across the switch element with a predetermined threshold voltage to generate a detection signal; a fault diagnosis circuit configured to perform a stuck-off diagnosis of the switch element by monitoring the detection signal at a timing when the drive signal of the switch element is at an on-logic level; A semiconductor device comprising:

2. 2. The semiconductor device according to claim 1, wherein the fault diagnosis circuit performs a stuck-on diagnosis of the switch element or a short circuit diagnosis of the light emitting element by monitoring the detection signal at a timing when the drive signal is at an off logic level.

3. 2. The semiconductor device according to claim 1, wherein said fault diagnosis circuit outputs a fault diagnosis result to an external device of said semiconductor device.

4. The semiconductor device according to claim 1 , wherein said fault diagnosis circuit transitions said semiconductor device to a safe state in response to a fault diagnosis result.

5. A control circuit configured to generate a control signal; a driver configured to generate the drive signal in response to the control signal; The semiconductor device according to claim 1 , further comprising:

6. The semiconductor device according to claim 5 , further comprising a level shifter configured to shift a signal level of the control signal between the control circuit and the driver.

7. A switch element or a current source configured to be connected in series to the light emitting element; a detection circuit configured to compare a voltage across the switch element or the current source with a predetermined threshold voltage to generate a detection signal; a fault diagnosis circuit configured to perform a stuck-on diagnosis of the switch element or the current source by monitoring the detection signal at a timing when the drive signal of the switch element or the current source is at an off-logic level; A semiconductor device comprising:

8. 8. The semiconductor device according to claim 7, wherein the fault diagnosis circuit performs a stuck-off diagnosis of the switch element or the current source, or a short circuit diagnosis or an open circuit diagnosis of the light-emitting element by monitoring the detection signal at a timing when the drive signal is at an on-logic level.

9. A switch element or a current source configured to be connected in series to the light emitting element; a detection circuit configured to detect a drive current flowing through the switch element or the current source and generate a detection signal; a fault diagnosis circuit configured to perform a stuck-on diagnosis of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an off state, and to perform a stuck-off diagnosis of the switch element or the current source by monitoring the detection signal at a timing when a drive signal of the switch element or the current source is at a logic level for an on state; A semiconductor device comprising:

10. The light-emitting element; A semiconductor device according to any one of claims 1 to 9, A light emitting device comprising:

11. The light emitting device according to claim 10 , wherein the light emitting element is an LED element or an organic EL element.

12. A vehicle comprising the light emitting device according to claim 10.