Semiconductor integrated circuit

Abstract

To provide a semiconductor integrated circuit capable of detecting power fault or ground fault regardless of a temperature.SOLUTION: In a power fault detection circuit 260, first ends of a first resistor R11 and a second resistor R12 are grounded to an installation line 206. A first switch SW11 is connected between the first resistor R11 and an output line 204, and is turned on when a low-side transistor ML is in an on-state. A first transistor Q11 is connected to the first resistor R11, and a second transistor Q12 is connected to the second resistor R12. A third resistor R13 is provided on a path of detection current being proportional to current flowing through the second transistor Q12. A determination circuit 270 generates a power fault detection signal SDET based on a comparison result between voltage drop (detection voltage) Vdet across the third resistor R13 and a threshold value voltage Vth. A fourth resistor R14 of a reference voltage source 290 has the temperature dependency of the same polarity as the third resistor R13, and thus the temperature dependency of determination conditions for a power fault state is made smaller.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a semiconductor integrated circuit.

Background Art

[0002] Semiconductor integrated circuits such as class-D amplifiers, DC / DC converters, and motor drivers include a switching circuit (inverter) including a high-side transistor and a low-side transistor.

[0003] When the low-side transistor is turned on with the output node of the switching circuit shorted to the power supply line (short to the power line), an overcurrent flows through the low-side transistor. Therefore, a semiconductor integrated circuit may be provided with a short-to-power detection circuit. Similarly, when the high-side transistor is turned on with the output node of the switching circuit shorted to the ground (short to the ground), an overcurrent flows through the high-side transistor. Therefore, a semiconductor integrated circuit may be provided with a short-to-ground detection circuit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] [Summary] The present disclosure has been made in such circumstances, and an exemplary object of one aspect thereof is to provide a semiconductor integrated circuit capable of detecting a short to the power supply line or a short to the ground regardless of temperature.

[0006] A semiconductor integrated circuit according to an aspect of the present disclosure includes a power supply line, an output line, and a ground line, an output stage including a high-side transistor connected between the power supply line and the output line and a low-side transistor connected between the output line and the ground line, a sky connection detection circuit that detects a sky connection of the output line, and a reference voltage source that supplies a threshold voltage to the sky connection detection circuit. The sky connection detection circuit includes a first resistor having a first end connected to the ground line, a second resistor having a first end connected to the ground line, a first switch connected between the second end of the first resistor and the output line and turning on when the low-side transistor is on, a first current source, a first N-type transistor having a first electrode connected to the second end of the first resistor, a control electrode connected to the first current source, and a second electrode, a second N-type transistor having a first electrode connected to the second end of the second resistor and a control electrode connected to the control electrode of the first transistor, a third resistor provided on a path of a detection current proportional to a current flowing through the second transistor, and a determination circuit that generates a sky connection detection signal based on a comparison result between a voltage drop across the third resistor and the threshold voltage. The reference voltage source includes a second current source that generates a reference current, and a series connection circuit including a fourth resistor and a MOS (Metal Oxide Semiconductor) transistor whose gate is biased at a constant voltage and connected in series on a path of the reference current, and the fourth resistor has a temperature dependence of the same polarity as that of the third resistor. The reference voltage source outputs a threshold voltage according to a voltage drop of the series connection circuit.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0008] [Detailed Description] (Overview of Embodiment) An overview of some exemplary embodiments of the present disclosure will be described. This overview is for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description that follows, and simplifies and describes some concepts of one or more embodiments. It is not intended to limit the scope of the invention or disclosure. This overview is not an exhaustive overview of all possible embodiments, nor is it intended to identify the important elements of all embodiments or to delineate the scope of some or all aspects. For convenience, "an embodiment" may be used to refer to one embodiment (example or variation) or a plurality of embodiments (examples or variations) disclosed in this specification.

[0009] A semiconductor integrated circuit according to an embodiment includes a power line, an output line, and a ground line, an output stage including a high-side transistor connected between the power line and the output line and a low-side transistor connected between the output line and the ground line, a floating node detection circuit that detects a floating node of the output line, and a reference voltage source that supplies a threshold voltage to the floating node detection circuit. The floating node detection circuit includes a first resistor having a first end connected to the ground line, a second resistor having a first end connected to the ground line, a first switch connected between a second end of the first resistor and the output line and turned on when the low-side transistor is on, a first current source, a first N-type transistor having a first electrode connected to the second end of the first resistor, a control electrode connected to the first current source, and a second electrode, a second N-type transistor having a first electrode connected to the second end of the second resistor and a control electrode connected to the control electrode of the first transistor, a third resistor provided on a path of a detection current proportional to a current flowing through the second transistor, and a determination circuit that generates a floating node detection signal based on a comparison result between a voltage drop of the third resistor and the threshold voltage. The reference voltage source includes a second current source that generates a reference current, and a series connection circuit including a fourth resistor and a MOS (Metal Oxide Semiconductor) transistor whose gate is biased at a constant voltage, connected in series on a path of the reference current, and the fourth resistor has a temperature dependence with the same polarity as the third resistor. The reference voltage source outputs a threshold voltage according to a voltage drop of the series connection circuit.

[0010] According to this configuration, by generating a threshold voltage using a fourth resistor having a temperature dependence with the same polarity as the third resistor, fluctuations in the resistance value of the third resistor can be canceled by the fourth resistor. Thereby, the temperature dependence of the determination condition for floating node detection can be further reduced.

[0011] In one embodiment, the third resistor and the fourth resistor may be resistor elements having the same structure.

[0012] In one embodiment, the third resistor and the fourth resistor may be polysilicon resistors.

[0013] In one embodiment, the reference voltage source may further include an amplifier that amplifies the voltage drop across the fourth resistor and outputs a threshold voltage. In this case, by using the gain of the amplifier as a design parameter, the temperature dependence of the determination condition for open-circuit detection can be reduced.

[0014] In one embodiment, the open-circuit detection circuit may further include a second switch connected between the second terminal of the first resistor and the ground line, which turns on when the high-side transistor is on.

[0015] In one embodiment, the semiconductor integrated circuit may further include a ground fault detection circuit that detects a ground fault in the output line. The ground fault detection circuit includes a fifth resistor having a first terminal connected to the power supply line, a sixth resistor having a first terminal connected to the power supply line, a third switch connected between the second terminal of the fifth resistor and the output line and turning on when the high-side transistor is on, a third current source, a P-type third transistor having a first electrode connected to the second terminal of the fifth resistor, a control electrode connected to the third current source, and a second electrode, a P-type fourth transistor having a first electrode connected to the second terminal of the sixth resistor and a control electrode connected to the control electrode of the third transistor, a seventh resistor provided on a path of a detection current proportional to the current flowing through the fourth transistor, and a determination circuit that generates a ground fault detection signal based on a comparison result between the voltage drop across the seventh resistor and the threshold voltage. The seventh resistor may have the same polarity temperature dependence as the third resistor and the fourth resistor.

[0016] According to this configuration, by generating the threshold voltage using the fourth resistor having the same polarity temperature dependence as the seventh resistor, the variation in the resistance value of the seventh resistor can be canceled by the fourth resistor. Thereby, the temperature dependence of the determination condition for ground fault detection can be reduced.

[0017] In one embodiment, the ground fault detection circuit may further include a fourth switch connected between the second terminal of the fifth resistor and the power supply line, which turns on when the low-side transistor is on.

[0018] A semiconductor integrated circuit according to an embodiment includes a power supply line, an output line, and a ground line, an output stage including a high-side transistor connected between the power supply line and the output line and a low-side transistor connected between the output line and the ground line, a ground fault detection circuit that detects a ground fault of the output line, and a reference voltage source that supplies a threshold voltage to the ground fault detection circuit. The ground fault detection circuit includes a fifth resistor having a first end connected to the power supply line, a sixth resistor having a first end connected to the power supply line, a third switch connected between a second end of the fifth resistor and the output line and turned on when the high-side transistor is on, a third current source, a P-type third transistor having a first electrode connected to the second end of the fifth resistor, a control electrode connected to the third current source, and a second electrode, a P-type fourth transistor having a first electrode connected to the second end of the sixth resistor and a control electrode connected to the control electrode of the third transistor, a seventh resistor provided on a path of a detection current proportional to a current flowing through the fourth transistor, and a determination circuit that generates a ground fault detection signal based on a comparison result between a voltage drop of the seventh resistor and the threshold voltage. The reference voltage source may include a second current source that generates a reference current, and a series connection circuit including a fourth resistor and a MOS transistor whose gate is biased, connected in series on a path of the reference current. The fourth resistor has a temperature dependence with the same polarity as the seventh resistor. The reference voltage source outputs a threshold voltage according to a voltage drop of the series connection circuit.

[0019] According to this configuration, by generating a threshold voltage using a fourth resistor having a temperature dependence with the same polarity as the seventh resistor, fluctuations in the resistance value of the seventh resistor can be canceled by the fourth resistor. Thereby, the temperature dependence of the determination condition for ground fault detection can be reduced.

[0020] In one embodiment, the seventh resistor and the fourth resistor may be resistor elements having the same structure.

[0021] In one embodiment, the seventh resistor and the fourth resistor may be polysilicon resistors.

[0022] In one embodiment, the reference voltage source may further include an amplifier that amplifies the voltage drop across the fourth resistor and outputs a threshold voltage. In this case, by using the gain of the amplifier as a design parameter, the temperature dependence of the determination condition for antenna disconnection detection can be further reduced.

[0023] In one embodiment, the ground fault detection circuit may further include a fourth switch connected between the second end of the fifth resistor and the power supply line, which turns on when the low-side transistor is on.

[0024] In one embodiment, the semiconductor integrated circuit may be an audio class-D amplifier.

[0025] In one embodiment, the semiconductor integrated circuit may be a switching regulator.

[0026] In one embodiment, the semiconductor integrated circuit may be for in-vehicle use.

[0027] (Embodiment) Hereinafter, preferred embodiments will be described with reference to the drawings. The same or equivalent components, members, and processes shown in the respective drawings are denoted by the same reference numerals, and duplicate explanations will be omitted as appropriate. Also, the embodiments are illustrative and not intended to limit the disclosure and the invention, and not all features and combinations thereof described in the embodiments are necessarily essential to the disclosure and the invention.

[0028] In this specification, the phrase "member A is in a state of being connected to member B" includes not only the case where member A and member B are physically directly connected, but also the case where member A and member B are indirectly connected via other members that do not substantially affect their electrical connection state or impair the functions and effects achieved by their combination.

[0029] Similarly, the phrase "member C is connected (provided) between member A and member B" includes not only the case where member A and member C, or member B and member C are directly connected, but also the case where they are indirectly connected via other members that do not substantially affect their electrical connection state or impair the functions and effects achieved by their combination.

[0030] In this specification, the symbols assigned to electrical signals such as voltage signals and current signals, or circuit elements such as resistors, capacitors, and inductors, represent their respective voltage values, current values, or circuit constants (resistance values, capacitance values, inductance), as required.

[0031] FIG. 1 is a circuit diagram of a semiconductor integrated circuit 200 according to an embodiment. The semiconductor integrated circuit 200 has a power supply terminal VCC, a switching terminal SW, a ground terminal GND, and a bootstrap terminal BS. A power supply voltage (input voltage) V CC is supplied to the power supply terminal VCC, and the ground terminal GND is grounded. An inductive element such as a coil of a speaker, a coil of a motor, or an inductor is connected to the switching terminal SW. A bootstrap capacitor C BS is connected between the bootstrap terminal BS and the switching terminal SW.

[0032] The semiconductor integrated circuit 200 generates one of a high-level voltage V CC , a low-level voltage 0V, and a high-impedance state at the switching terminal SW.

[0033] The semiconductor integrated circuit 200 includes a power supply line 202, an output line (also referred to as a switching line) 204, a ground line 206, a bootstrap line 208, a rectifying element 209, a high-side driver 210, a low-side driver 220, a level shifter 230, a ground fault detection circuit 240, a floating fault detection circuit 260, and a reference voltage source 290.

[0034] The power line 202 is connected to the power supply terminal VCC. The output line 204 is connected to the switching terminal SW. The ground line 206 is connected to the ground terminal GND. The bootstrap line 208 is connected to the bootstrap terminal BS. A constant voltage V REG generated by a power supply circuit (not shown) is supplied to the bootstrap terminal BS via a rectifying element 209. The rectifying element 209 may be a diode whose cathode is connected to the bootstrap line 208 and whose anode receives the constant voltage V REG . The rectifying element 209 may be a synchronous rectifying switch that switches in synchronization with the high-side transistor MH. The rectifying element 209 and an external bootstrap capacitor C BS form a bootstrap circuit, and generate a bootstrap voltage V SW on the bootstrap line 208 that is higher than the switching voltage V REG generated at the switching terminal SW (output line 204) by V BS - Vf. Vf is the forward voltage of the rectifying element 209.

[0035] The high-side transistor MH and the low-side transistor ML are N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The high-side transistor MH is connected between the power line 202 and the output line 204, and the low-side transistor ML is connected between the output line 204 and the ground line 206.

[0036] The level shifter 230 level-shifts the control signal HIN upward and delivers it to the high-side driver 210. The high-side driver 210 drives the high-side transistor MH according to the control signal HIN. The low-side driver 220 drives the low-side transistor ML according to the control signal LIN.

[0037] When the high-side transistor MH is on and the low-side transistor ML is off, the switching voltage V SW is at a high-level voltage VCC When the high-side transistor MH is off and the low-side transistor ML is on, the switching voltage V SW is the low-level voltage 0V. When both the high-side transistor MH and the low-side transistor ML are off, the switching terminal SW has a high impedance.

[0038] The open-circuit detection circuit 260 is enabled in the low-output state where the high-side transistor MH is off and the low-side transistor ML is on. The open-circuit detection circuit 260 can detect an open-circuit abnormality of the switching terminal SW in the enabled state, and when detecting an open-circuit abnormality, asserts (for example, a high level) an open-circuit detection signal SDET. The gate signal of the low-side transistor ML is supplied to the open-circuit detection circuit 260 as an active-high enable signal EN.

[0039] The short-circuit detection circuit 240 is enabled in the high-output state where the high-side transistor MH is on and the low-side transistor ML is off. The short-circuit detection circuit 240 can detect a short-circuit abnormality of the switching terminal GND in the enabled state, and when detecting a short-circuit abnormality, asserts (for example, a high level) a short-circuit detection signal GDET. The gate signal of the high-side transistor MH is supplied to the short-circuit detection circuit 240 as an active-high enable signal EN.

[0040] The reference voltage source 290 supplies a threshold voltage Vth to the open-circuit detection circuit 260 and the short-circuit detection circuit 240.

[0041] FIG. 2 is a circuit diagram of the open-circuit detection circuit 260 and the reference voltage source 290 according to the embodiment. First, the open-circuit detection circuit 260 will be described. The open-circuit detection circuit 260 includes a first switch SW11, a second switch SW12, a first current source 262, a first resistor R11, a second resistor R12, a first transistor Q11, a second transistor Q12, a current mirror circuit 264, and a determination circuit 270. A power supply voltage V REGD is supplied to the power supply line 203.

[0042] The first end of the first resistor R11 is connected to the ground line 206. The first end of the second resistor R12 is connected to the ground line 206.

[0043] The first switch SW11 is connected between the second end of the first resistor R11 and the output line 204. The first switch SW11 turns on when the low-side transistor ML is on. For example, the first switch SW11 is an NMOS transistor, and its gate is supplied with the gate signal of the low-side transistor ML.

[0044] The second switch SW12 is connected between the ground line 206 and the second end of the first resistor R11, and turns on when the low-side transistor ML is off.

[0045] When the first switch SW11 is on and the second switch SW12 is off, the antenna detection circuit 260 is in an enabled state. When the first switch SW11 is off and the second switch SW12 is on, the antenna detection circuit 260 is in a disabled state.

[0046] The first transistor Q11 is an NPN bipolar transistor, and its first electrode (emitter) is connected to the second end of the first resistor R11. The second electrode (collector) and the control electrode (base) of the first transistor Q11 are connected to the first current source 262. The first current source 262 includes, for example, a reference current source 263 and a current mirror circuit CM10. The current mirror circuit CM10 sources a constant current Ic that is the mirror ratio times the reference current Iref generated by the reference current source 263.

[0047] The second transistor Q12 is an NPN bipolar transistor of the same type as the first transistor Q11. Its first electrode (emitter) is connected to the second end of the second resistor R12, and its control electrode (base) is connected to the control electrode (base) of the first transistor Q11.

[0048] The current mirror circuit 264 folds back the current Idet flowing through the second transistor Q12.

[0049] The third resistor R13 is connected between the output node 265 of the current mirror circuit 264 and the ground line 206. A voltage drop proportional to the output current Idet’ of the current mirror circuit 264 occurs across the third resistor R13. Vdet = R13 × Idet’ …(1)

[0050] The determination circuit 270 generates a sky connection detection signal SDET based on the comparison result between the voltage drop (detection voltage) Vdet of the third resistor R13 and a predetermined threshold voltage Vth. Specifically, the determination circuit 270 asserts the sky connection detection signal SDET when Vdet > Vth.

[0051] In this embodiment, the determination circuit 270 includes a comparator 272, a filter 274, a filter 276, and an AND gate 278. The comparator 272 compares the detection voltage Vdet with the threshold voltage Vth. The filter 274 is a low-pass filter that removes the high-frequency components of the output signal COMP of the comparator 272. By the filter 274, noise components are removed. The filter 276 is a low-pass filter that removes the high-frequency components of the gate signal of the low-side transistor LH which is the enable signal EN. The output of the filter 276 becomes a mask signal MSK that is at a high level when the sky connection detection circuit 260 is in an enabled state. The AND gate 278 takes the logical product of the output of the filter 274 and the mask signal MSK and outputs it as the sky connection detection signal SDET.

[0052] Next, the reference voltage source 290 will be described. The reference voltage source 290 includes a second current source 292, a fourth resistor R14, MOS transistors M11 to M13, and an amplifier 296.

[0053] The second current source 292 generates a reference current Ir. For example, the second current source 292 includes a reference current source 293 and a current mirror circuit CM11. The current mirror circuit CM11 has a current amplification factor (mirror ratio) A, and sources a constant current Ir (= Iref × A) which is A times the reference current Iref generated by the reference current source 293. The current amplification factor A may be 1, may be greater than 1, or may be less than 1.

[0054] The fourth resistor R14 and the MOS transistors M11 to M13 are connected in series, and the series connection circuit 294 including them is provided on the path of the reference current Ir. The gates of the MOS transistors M11 to M13 are biased by a constant voltage V REG . The constant voltage V REG may be substantially the same voltage level as the gate high voltage of the low side transistor ML. A voltage drop (reference voltage) Vr based on the reference current Ir occurs in the series connection circuit 294. The reference voltage Vr is represented by Equation (2). Vr = Vds + R14 × Ir …(2) Vds is the sum of the drain-source voltages of the MOS transistors M11 to M13.

[0055] The fourth resistor R14 has the same polarity temperature dependence as the third resistor R13. The third resistor R13 and the fourth resistor R14 preferably have the same element structure. For example, the third resistor R13 and the fourth resistor R14 may be polysilicon resistors having negative temperature characteristics.

[0056] The reference voltage source 290 outputs a threshold voltage Vth corresponding to the reference voltage Vr. In this example, the reference voltage source 290 includes an amplifier 296 and outputs, as the threshold voltage Vth, a voltage obtained by amplifying the voltage drop Vr. The amplifier 296 is, for example, a non-inverting amplifier and includes an operational amplifier OA31 and resistors R31, R32. The threshold voltage Vth is represented by Equation (3). Vth = g × Vr = g × (Vds + R14 × Ir) …(3) g is the gain of the amplifier 296 and g = (R31 + R32) / R31.

[0057] The above is the configuration of the antenna short - circuit detection circuit 260 and the reference voltage source 290. Subsequently, the operation of the antenna short - circuit detection circuit 260 will be described.

[0058] Figure 3 is a circuit diagram for explaining the antenna short - circuit detection of the antenna short - circuit detection circuit 260. The switching terminal SW is short - circuited (antenna short - circuit) to the power supply line 202 via the antenna path 4, and a short - circuit current flows through the low - side transistor ML. At this time, in the antenna short - circuit detection circuit 260, the short - circuit current Ishort flows through the antenna path 4, the first switch SW11, and the first resistor R11.

[0059] Since the total current of the short - circuit current Ishort and the current Ic generated by the first current source 262 flows through the first resistor R11, the voltage Ve at the emitter of the first transistor Q11 is expressed by Equation (3). Ve = R11×(Ishort + Ic) …(3)

[0060] Since the base - emitter voltage of the first transistor Q11 and the base - emitter voltage of the second transistor Q12 are substantially equal, the same voltage as the emitter voltage Ve of the first transistor Q11 is also generated at the emitter of the second transistor Q12. At this time, the detection current Idet expressed by Equation (4) flows through the second resistor R12. Idet = Ve / R12 = R11×(Ishort + Ic) / R12 …(4)

[0061] When R11 = R12, Idet=(Ishort + Ic) …(4’) It becomes.

[0062] This detection current Idet is folded back by the current mirror circuit 264, and the detection current Idet’ is supplied to the third resistor R13. When the current amplification factor (mirror ratio) of the current mirror circuit 264 is α, the detection current Idet’ is expressed by Equation (5). Idet’ = Idet×α …(5) The current amplification factor α may be 1 or may be a value greater than 1.

[0063] When the detection current Idet’ flows, the voltage drop generated across the third resistor R13 becomes the detection voltage Vdet and is represented by Equation (6). Vdet = Idet’ × R13 = α × (Ishort + Ic) × R13 …(6)

[0064] The threshold voltage Vth is determined to be higher than the detection voltage Vdet when there is no sky connection (Ishort = 0) and lower than the detection voltage Vdet when a sky connection occurs (Ishort > 0). When a sky connection occurs and a large short-circuit current Ishort flows, Vdet > Vth, and the sky connection detection signal GDET is asserted.

[0065] Thus, according to the semiconductor integrated circuit 200 according to the embodiment, the sky connection of the switching terminal SW can be detected by the sky connection detection circuit 260.

[0066] The determination circuit 270 compares the detection voltage Vdet represented by Equation (6) with the threshold voltage Vth represented by Equation (3). Vdet = Idet’ × R13 = α × (Ishort + Ic) × R13 …(6) Vth = g × Vr = g × (Vds + R14 × Ir) …(3)

[0067] When the third resistor R13 has a negative temperature characteristic, the detection voltage Vdet also has a negative temperature characteristic. If the threshold voltage Vth has no temperature dependence or has a positive temperature characteristic, the determination condition for the sky connection state will vary greatly with temperature.

[0068] On the other hand, in this embodiment, the fourth resistor R14 has the same polarity (negative) temperature characteristic as the third resistor R13. Therefore, the threshold voltage Vth represented by Equation (3) also has a negative temperature dependence and follows the temperature variation of the detection voltage Vdet. Thereby, the temperature dependence of the determination condition for the sky connection state can be reduced.

[0069] Specifically, according to the reference voltage source 290 in FIG. 2, it is possible to design the voltage level of the threshold voltage Vth and its temperature characteristics using the number of MOS transistors M11 to M13, the element size, the resistance value of the fourth resistor R14, and the gain g as parameters. When the gain g = 1, the amplifier 296 can be omitted.

[0070] Subsequently, the ground fault detection circuit 240 will be described.

[0071] FIG. 4 is a circuit diagram of the ground fault detection circuit 240 according to the embodiment. The ground fault detection circuit 240 has a configuration in which the sky and ground (power line and ground line) of the sky fault detection circuit 260 are inverted and the P-type transistor and the N-type transistor are interchanged.

[0072] The ground fault detection circuit 240 includes a third switch SW21, a fourth switch SW22, a third current source 242, a fifth resistor R21, a sixth resistor R22, a seventh resistor R23, a third transistor Q21, a fourth transistor Q22, a level shifter 246, and a determination circuit 250.

[0073] The first end of the fifth resistor R21 is connected to the power line 202. The first end of the sixth resistor R22 is connected to the power line 202. A power supply voltage V CC is supplied to the power line 202.

[0074] The third switch SW21 is connected between the second end of the fifth resistor R21 and the output line 204. The third switch SW21 turns on when the high-side transistor MH is on. For example, the third switch SW21 is an NMOS transistor, and the gate signal of the high-side transistor MH is supplied to its gate.

[0075] The fourth switch SW22 is connected between the power line 202 and the second end of the fifth resistor R21, and turns on when the high-side transistor MH is off and the low-side transistor ML is on.

[0076] When the third switch SW21 is on and the fourth switch SW22 is off, the ground fault detection circuit 240 is in an enabled state. When the third switch SW21 is off and the fourth switch SW22 is on, the ground fault detection circuit 240 is in a disabled state.

[0077] The third transistor Q21 is a PNP bipolar transistor, and the first electrode (emitter) is connected to the second end of the fifth resistor R21. The second electrode (collector) and the control electrode (base) of the third transistor Q21 are connected to the third current source 242. The third current source 242 includes, for example, the first current source 243 and the current mirror circuit CM10, and sinks a constant current Ic.

[0078] The fourth transistor Q22 is a PNP bipolar transistor of the same type as the third transistor Q21. The first electrode (emitter) is connected to the second end of the sixth resistor R22, and the control electrode (base) is connected to the control electrode (base) of the third transistor Q21.

[0079] The seventh resistor R23 is provided on the path of the detection current Idet flowing through the fourth transistor Q22 or a current Idet' proportional thereto. A voltage drop proportional to the detection current Idet(Idet)' occurs across the seventh resistor R23. Vdet = R23×Idet

[0080] The determination circuit 250 generates a ground fault detection signal GDET based on the comparison result between the voltage drop (detection voltage) Vdet of the seventh resistor R23 and a predetermined threshold voltage Vth. Specifically, the determination circuit 250 asserts the ground fault detection signal GDET when Vdet > Vth. The threshold voltage Vth is generated by a reference voltage source 290 having the configuration shown in FIG. 2.

[0081] In this embodiment, the determination circuit 250 includes a comparator 252, a filter 254, a filter 256, and an AND gate 258. The comparator 252 compares the detected voltage Vdet with a predetermined threshold voltage Vth. The filter 254 is a low-pass filter that removes the high-frequency components of the output signal COMP of the comparator 252. By the filter 254, noise components are removed. The level shifter 246 level-shifts down the gate signal of the high-side transistor MH which is the enable signal EN. The filter 256 is a low-pass filter that removes the high-frequency components of the output of the level shifter 246. The output of the level shifter 246 becomes a mask signal MSK that is at a high level when the ground fault detection circuit 240 is in an enabled state. The AND gate 258 takes the logical product of the output of the filter 254 and the mask signal MSK, and outputs it as the ground fault detection signal GDET.

[0082] The above is the configuration of the ground fault detection circuit 240. According to this ground fault detection circuit 240, by operating in the same manner as the open circuit detection circuit 260, it is possible to detect a ground fault at the output terminal SW.

[0083] Similar to what has been described for the open circuit detection circuit 260, according to the ground fault detection circuit 240, the temperature dependence of the determination condition for ground fault detection can be reduced.

[0084] Modification examples of the open circuit detection circuit 260 and the ground fault detection circuit 240 will be described. Regarding the open circuit detection circuit 260, the first switch SW11 may be composed of a PMOS transistor. Also, the second switch SW12 may be omitted. Regarding the ground fault detection circuit 240, the fourth switch SW22 may be composed of an NMOS transistor similar to the high-side transistor MH. Alternatively, the fourth switch SW22 may be omitted.

[0085] The configuration of the determination circuit 270 is not limited to that in FIG. 2. For voltage comparison, circuit elements other than a voltage comparator may be used. For example, a MOS transistor may be used as the voltage comparison means. The same applies to the determination circuit 250.

[0086] In the embodiment, the semiconductor integrated circuit 200 including both the sky connection detection circuit 260 and the ground connection detection circuit 240 has been described, but only one of them may be provided.

[0087] Subsequently, the use of the switching circuit will be described.

[0088] FIG. 5 is a block diagram of an audio system 400. The audio system 400 includes an audio IC 200C, a speaker 402, a filter 404, a bootstrap capacitor C BS , and a battery 410.

[0089] The audio IC 200C is a class-D amplifier and includes a high-side transistor MH, a low-side transistor ML, a high-side driver 210, a low-side driver 220, level shifters 230, 232, a ground connection detection circuit 240, and a pulse width modulator 310. The high-side transistor MH is connected between the power supply pin VCC and the switching pin SW, and the low-side transistor ML is connected between the switching pin SW and the ground pin GND.

[0090] The pulse width modulator 310 converts the audio signal V AUD into a PWM (pulse width modulation) signal and generates control signals HIN and LIN.

[0091] The control signal HIN is level-shifted up by the level shifter 230 and supplied to the high-side driver 210.

[0092] The level shifter 232 is provided as a dummy to equalize the delay amounts between the high side and the low side. The level shifter 232 may be omitted. The low-side driver 220 drives the low-side transistor ML in response to the output of the level shifter 232.

[0093] FIG. 6 is a block diagram of the step-down converter 500. The step-down converter 500 includes a controller IC200D and a main circuit 510 of the step-down converter. The step-down converter 500 receives the power supply voltage V from the battery 506 as the input voltage V via the input line 502, steps it down to an output voltage V having a predetermined voltage level, and supplies it to a load (not shown) connected to the output line 504. The main circuit 510 includes a high-side transistor MH, a low-side transistor ML, an inductor L2, and an output capacitor C2. BAT and receives it as the input voltage V via the input line 502, steps it down to an output voltage V having a predetermined voltage level, and supplies it to a load (not shown) connected to the output line 504. The main circuit 510 includes a high-side transistor MH, a low-side transistor ML, an inductor L2, and an output capacitor C2. CC and receives it as the input voltage V via the input line 502, steps it down to an output voltage V having a predetermined voltage level, and supplies it to a load (not shown) connected to the output line 504. The main circuit 510 includes a high-side transistor MH, a low-side transistor ML, an inductor L2, and an output capacitor C2. OUT and receives it as the input voltage V via the input line 502, steps it down to an output voltage V having a predetermined voltage level, and supplies it to a load (not shown) connected to the output line 504. The main circuit 510 includes a high-side transistor MH, a low-side transistor ML, an inductor L2, and an output capacitor C2.

[0094] The controller IC200D includes a high-side transistor MH, a low-side transistor ML, a high-side driver 210, a low-side driver 220, a level shifter 230, a ground fault detection circuit 240, and a feedback circuit 320. Resistors R41 and R42 divide the output voltage V, and supply the divided feedback voltage V to the feedback pin FB of the controller IC200D. OUT and supply the divided feedback voltage V to the feedback pin FB of the controller IC200D. FB and supply the divided feedback voltage V to the feedback pin FB of the controller IC200D.

[0095] The feedback circuit 320 generates a PWM signal whose duty cycle is adjusted so that the feedback voltage V approaches a predetermined reference voltage V. The feedback circuit 320 generates control signals HIN and LIN according to the PWM signal. The level shifter 230 level-shifts the control signal HIN and supplies it to the high-side driver 210. Also, the control signal LIN is directly supplied to the low-side driver 220. A dummy level shifter may be inserted between the feedback circuit 320 and the low-side driver 220. FB and generates a PWM signal whose duty cycle is adjusted so that the feedback voltage V approaches a predetermined reference voltage V. The feedback circuit 320 generates control signals HIN and LIN according to the PWM signal. The level shifter 230 level-shifts the control signal HIN and supplies it to the high-side driver 210. Also, the control signal LIN is directly supplied to the low-side driver 220. A dummy level shifter may be inserted between the feedback circuit 320 and the low-side driver 220. REF and generates a PWM signal whose duty cycle is adjusted so that the feedback voltage V approaches a predetermined reference voltage V. The feedback circuit 320 generates control signals HIN and LIN according to the PWM signal. The level shifter 230 level-shifts the control signal HIN and supplies it to the high-side driver 210. Also, the control signal LIN is directly supplied to the low-side driver 220. A dummy level shifter may be inserted between the feedback circuit 320 and the low-side driver 220.

[0096] The step-down converter 500 may be of a diode rectification type. In that case, a rectifier diode is connected instead of the low-side transistor ML, and the low-side driver 220 is omitted.

[0097] (Appendix) The following techniques are disclosed in this specification.

[0098] (Item 1) A power line, an output line, and a ground line, an output stage including a high-side transistor connected between the power line and the output line and a low-side transistor connected between the output line and the ground line, a floating detection circuit for detecting the floating of the output line, a reference voltage source for supplying a threshold voltage to the floating detection circuit, and comprising, the floating detection circuit includes, a first resistor having a first end connected to the ground line, a second resistor having a first end connected to the ground line, a first switch connected between a second end of the first resistor and the output line and turning on when the low-side transistor is on, a first current source, an N-type first transistor having a first electrode connected to the second end of the first resistor, a control electrode connected to the first current source, and a second electrode, an N-type second transistor having a first electrode connected to the second end of the second resistor and a control electrode connected to the control electrode of the first transistor, a third resistor provided on a path of a detection current proportional to the current flowing through the second transistor, a determination circuit for generating a floating detection signal based on a comparison result between a voltage drop across the third resistor and the threshold voltage, and comprising, the reference voltage source includes, a second current source for generating a reference current, a series connection circuit including a fourth resistor and a MOS (Metal Oxide Semiconductor) transistor whose gate is biased at a constant voltage and connected in series on a path of the reference current, and the fourth resistor has a temperature dependence with the same polarity as the third resistor and outputs the threshold voltage corresponding to a voltage drop of the series connection circuit, a semiconductor integrated circuit.

[0099] (Item 2) The semiconductor integrated circuit according to item 1, wherein the third resistor and the fourth resistor are resistor elements having the same structure.

[0100] (Item 3) The semiconductor integrated circuit according to item 2, wherein the third resistor and the fourth resistor are polysilicon resistors.

[0101] (Item 4) The semiconductor integrated circuit according to any one of items 1 to 3, wherein the reference voltage source further includes an amplifier that amplifies the voltage drop of the fourth resistor and outputs the threshold voltage.

[0102] (Item 5) The semiconductor integrated circuit according to any one of items 1 to 4, wherein the ground fault detection circuit is connected between the second end of the first resistor and the ground line, and further includes a second switch that turns on when the high-side transistor is on.

[0103] (Item 6) Further comprising a ground fault detection circuit for detecting a ground fault of the output line, The ground fault detection circuit is A fifth resistor having a first end connected to the power supply line, A sixth resistor having a first end connected to the power supply line, A third switch connected between the second end of the fifth resistor and the output line, and turning on when the high-side transistor is on, A third current source, A P-type third transistor having a first electrode connected to the second end of the fifth resistor, and having a control electrode and a second electrode connected to the third current source, A P-type fourth transistor having a first electrode connected to the second end of the sixth resistor, and having a control electrode connected to the control electrode of the third transistor, A seventh resistor provided on a path of a detection current proportional to the current flowing through the fourth transistor, A determination circuit that generates a ground fault detection signal based on a comparison result between the voltage drop of the seventh resistor and the threshold voltage; The semiconductor integrated circuit according to any one of items 1 to 5, comprising the seventh resistor having a temperature dependence with the same polarity as the third resistor and the fourth resistor.

[0104] (Item 7) The semiconductor integrated circuit according to item 6, wherein the ground fault detection circuit is connected between the second end of the fifth resistor and the power supply line, and further includes a fourth switch that turns on when the low-side transistor is on.

[0105] (Item 8) A power supply line, an output line, and a ground line, An output stage including a high-side transistor connected between the power supply line and the output line and a low-side transistor connected between the output line and the ground line, A ground fault detection circuit that detects a ground fault of the output line, A reference voltage source that supplies a threshold voltage to the ground fault detection circuit, Comprising The ground fault detection circuit A fifth resistor having a first end connected to the power supply line, A sixth resistor having a first end connected to the power supply line, A third switch connected between the second end of the fifth resistor and the output line and that turns on when the high-side transistor is on, A third current source, A P-type third transistor having a first electrode connected to the second end of the fifth resistor, a control electrode connected to the third current source, and a second electrode, A P-type fourth transistor having a first electrode connected to the second end of the sixth resistor and a control electrode connected to the control electrode of the third transistor, A seventh resistor provided on a path of a detection current proportional to the current flowing through the fourth transistor, A determination circuit that generates a ground fault detection signal based on a comparison result between the voltage drop of the seventh resistor and the threshold voltage; comprising The reference voltage source a second current source that generates a reference current; a series connection circuit including a fourth resistor and a MOS transistor with a biased gate connected in series on the path of the reference current; and the fourth resistor has a temperature dependence with the same polarity as the seventh resistor, and outputs the threshold voltage according to the voltage drop of the series connection circuit, a semiconductor integrated circuit.

[0106] (Item 9) The semiconductor integrated circuit according to item 8, wherein the seventh resistor and the fourth resistor are resistor elements having the same structure.

[0107] (Item 10) The semiconductor integrated circuit according to item 9, wherein the seventh resistor and the fourth resistor are polysilicon resistors.

[0108] (Item 11) The semiconductor integrated circuit according to any one of items 8 to 10, wherein the reference voltage source further includes an amplifier that amplifies the voltage drop of the fourth resistor and outputs the threshold voltage.

[0109] (Item 12) The semiconductor integrated circuit according to any one of items 8 to 11, wherein the ground fault detection circuit is connected between the second end of the fifth resistor and the power supply line, and further includes a fourth switch that turns on when the low-side transistor is on.

[0110] (Item 13) The semiconductor integrated circuit according to any one of items 1 to 12, which is an audio class D amplifier.

[0111] (Item 14) The semiconductor integrated circuit according to any one of items 1 to 12, which is a switching regulator.

[0112] (Item 15) The semiconductor integrated circuit according to any one of Items 1 to 12, which is for vehicle use.

[0113] Regarding the embodiments according to the present disclosure, specific terms have been used for explanation, but this explanation is merely an exemplification for aiding understanding and does not limit the present disclosure or the scope of the claims. The scope of the present invention is defined by the scope of the claims, and thus, embodiments, examples, and modifications not described herein are also included in the scope of the present invention.

Explanation of Reference Numerals

[0114] 200 Semiconductor integrated circuit 210 High-side driver 220 Low-side driver 230 Level shifter MH High-side transistor ML Low-side transistor VCC Power supply terminal SW Switching terminal GND Ground terminal BS Bootstrap terminal 202 Power supply line 204 Switching line 206 Ground line 208 Bootstrap line 209 Rectifying element 240 Ground fault detection circuit SW21 Third switch SW22 Fourth switch R21 Fifth resistor R22 Sixth resistor R23 Seventh resistor Q21 Third transistor Q22 Fourth transistor 242 Current source 246 Level shifter 250 Judgment circuit 252 Comparator 254, 256 Filters 258 AND gate 260 Open circuit detection circuit SW11 First Switch SW12 Second Switch R11 First Resistor R12 Second Resistor R13 Third Resistor Q11 First Transistor Q12 Second Transistor 262 First Current Source 263 Reference Current Source 264 Current Mirror Circuit 270 Judgment Circuit 272 Comparator 274,276 Filter 278 AND Gate 290 Reference Voltage Source 292 Second Current Source 293 Reference Current Source CM11 Current Mirror Circuit R14 Fourth Resistor M11 MOS Transistor 294 Series Connection Circuit 296 Amplifier OA31 Operational Amplifier R31,R32 Resistors 200C Audio IC 200D Controller IC 400 Audio System 402 Speaker 404 Filter 500 Step-down Converter 502 Input Line 504 Output Line 510 Main Circuit

Claims

1. A power line, an output line, and a ground line, an output stage including a high-side transistor connected between the power line and the output line and a low-side transistor connected between the output line and the ground line, a floating detection circuit for detecting a floating of the output line, a reference voltage source for supplying a threshold voltage to the floating detection circuit, characterized in that, the floating detection circuit includes a first resistor having a first end connected to the ground line, a second resistor having a first end connected to the ground line, a first switch connected between a second end of the first resistor and the output line and turning on when the low-side transistor is on, a first current source, an N-type first transistor having a first electrode connected to the second end of the first resistor, a control electrode connected to the first current source, and a second electrode, an N-type second transistor having a first electrode connected to the second end of the second resistor and a control electrode connected to the control electrode of the first transistor, a third resistor provided on a path of a detection current proportional to a current flowing through the second transistor, a determination circuit for generating a floating detection signal based on a comparison result between a voltage drop across the third resistor and the threshold voltage, characterized in that, the reference voltage source includes a second current source for generating a reference current, a series connection circuit including a fourth resistor connected in series on a path of the reference current and a MOS (Metal Oxide Semiconductor) transistor whose gate is biased at a constant voltage, wherein the fourth resistor has a temperature dependence with the same polarity as the third resistor and outputs the threshold voltage corresponding to a voltage drop across the series connection circuit, a semiconductor integrated circuit.

2. The semiconductor integrated circuit according to claim 1, wherein the third resistor and the fourth resistor are resistor elements having the same structure.

3. The semiconductor integrated circuit according to claim 2, wherein the third resistor and the fourth resistor are polysilicon resistors.

4. The semiconductor integrated circuit according to any one of claims 1 to 3, wherein the reference voltage source further includes an amplifier for amplifying the voltage drop across the fourth resistor and outputting the threshold voltage.

5. The semiconductor integrated circuit according to any one of claims 1 to 3, wherein the floating detection circuit further includes a second switch connected between the second end of the first resistor and the ground line and turning on when the high-side transistor is on.

6. Further comprising a ground fault detection circuit for detecting a ground fault of the output line, The ground fault detection circuit is, A fifth resistor having a first end connected to the power supply line, A sixth resistor having a first end connected to the power supply line, A third switch connected between the second end of the fifth resistor and the output line and turned on when the high-side transistor is on, A third current source, A P-type third transistor having a first electrode connected to the second end of the fifth resistor, a control electrode connected to the third current source, and a second electrode, A P-type fourth transistor having a first electrode connected to the second end of the sixth resistor and a control electrode connected to the control electrode of the third transistor, A seventh resistor provided on a path of a detection current proportional to the current flowing through the fourth transistor, A determination circuit for generating a ground fault detection signal based on a comparison result between the voltage drop across the seventh resistor and the threshold voltage, The semiconductor integrated circuit according to any one of claims 1 to 3, wherein the seventh resistor has a temperature dependence of the same polarity as that of the third resistor and the fourth resistor.

7. The semiconductor integrated circuit according to claim 6, wherein the ground fault detection circuit further includes a fourth switch connected between the second end of the fifth resistor and the power supply line and turned on when the low-side transistor is on.

8. A power supply line, an output line, and a ground line, An output stage including a high-side transistor connected between the power supply line and the output line and a low-side transistor connected between the output line and the ground line, A ground fault detection circuit for detecting a ground fault of the output line, A reference voltage source for supplying a threshold voltage to the ground fault detection circuit, Comprising, The ground fault detection circuit is, A fifth resistor having a first end connected to the power supply line, A sixth resistor having a first end connected to the power supply line, A third switch connected between the second end of the fifth resistor and the output line and turned on when the high-side transistor is on, A third current source, A P-type third transistor having a first electrode connected to the second end of the fifth resistor, a control electrode connected to the third current source, and a second electrode, A P-type fourth transistor having a first electrode connected to the second end of the sixth resistor and a control electrode connected to the control electrode of the third transistor, A seventh resistor provided on a path of a detection current proportional to a current flowing through the fourth transistor; A determination circuit that generates a ground fault detection signal based on a comparison result between a voltage drop of the seventh resistor and the threshold voltage; Comprising; The reference voltage source is; A second current source that generates a reference current; A series connection circuit including a fourth resistor and a MOS transistor with a biased gate connected in series on a path of the reference current; Including, the fourth resistor has a temperature dependence with the same polarity as the seventh resistor, and outputs the threshold voltage according to a voltage drop of the series connection circuit, a semiconductor integrated circuit.

9. The semiconductor integrated circuit according to claim 8, wherein the seventh resistor and the fourth resistor are resistor elements having the same structure.

10. The semiconductor integrated circuit according to claim 9, wherein the seventh resistor and the fourth resistor are polysilicon resistors.

11. The semiconductor integrated circuit according to claim 8, wherein the reference voltage source further includes an amplifier that amplifies the voltage drop of the fourth resistor and outputs the threshold voltage.

12. The semiconductor integrated circuit according to claim 8, wherein the ground fault detection circuit is connected between a second end of the fifth resistor and the power supply line, and further includes a fourth switch that turns on when the low-side transistor is on.

13. The semiconductor integrated circuit according to any one of claims 1 to 3, which is an audio class-D amplifier.

14. The semiconductor integrated circuit according to any one of claims 1 to 3, which is a switching regulator.

15. The semiconductor integrated circuit according to any one of claims 1 to 3, which is for in-vehicle use.

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