KR102100861B1 - An Apparatus And A Method For Testing A Low-side Driving IC - Google Patents

Abstract

According to an embodiment of the present invention, provided is a low-side driving IC, which includes a load driving transistor, a load driving driver, a control unit, shunt resistance, a back-to-back diode, a failure detection unit, and a ground opening detection unit. The failure detection unit can detect a short circuit in a battery of a low-side output terminal, a short circuit in a low-side ground, and the opening of the load, and the ground opening detection unit can detect the opening of the low-side ground.

Description

Fault diagnosis device and method for low-side driving IC {An Apparatus And A Method For Testing A Low-side Driving IC}

The present invention relates to an electronic control device, and more particularly, to a low-side driving IC failure diagnosis apparatus and method for detecting a failure of the low-side driving IC output terminal.

In general, various actuators belonging to an electronically controlled fuel injection device in a vehicle are electronically controlled through an engine control unit, and the combustion state is changed by changing the air-fuel ratio of the mixer according to the use environment or operating conditions of the engine. It performs the function of optimizing.

The actuator (load) is driven by controlling and supplying current through a driving circuit, and stable driving of the actuator has a significant effect on vehicle safety. Therefore, it is important that the current is precisely monitored and controlled in order to accurately control the actuator.

However, in recent years, due to an increase in electronic components in a vehicle, such as an engine controller (ECU) and an actuator, failures in the actuator (load) driving circuit frequently occur, which may increase vehicle safety.

In particular, a ground open (OG) failure may occur at the output terminal of the actuator driving circuit. When the controller is mass-produced, the wire bonding in the semiconductor package is passed over time even if the ground of the actuator driving circuit is normally connected to the controller ground. (Wire Bonding) When the connection is disconnected or a soldering (solder) connection between the actuator's ground pin and the PCB ground occurs, a ground opening failure may occur at the output terminal of the actuator driving circuit.

In addition, if the output transistor of the actuator driving circuit is turned on while the ground of the actuator driving circuit is open, the output current cannot escape outside the actuator driving circuit, and the current can escape through the circuit to the ground of another power domain. do. At this time, since a large current flows inside the actuator driving circuit, the reference voltage of the actuator driving circuit changes, which may cause malfunction and reset, and in severe cases, a serious failure such as destruction of the actuator driving circuit may occur.

The present invention has been devised to meet the above-mentioned needs, and to provide a low-side driving IC fault diagnosis apparatus and method capable of detecting ground open (OG, Open Ground) of a low-side driving IC output.

A low-side driving IC according to an embodiment of the present invention includes a load driving transistor for driving a load connected between a battery and a low-side output terminal; A load driving driver for controlling the load driving transistor; A control unit connected to the load driving driver and applying a driving signal for driving the load driving transistor to the load driving driver; A shunt resistor connected in series between the load and the low side ground; A back-to-back diode connected between the low-side ground and another shunt resistor connected to another power domain-in ground; A fault detector for detecting a fault based on a potential across the shunt resistor that changes as the load driving transistor is turned on or off; And a ground open detection unit connected between the load driving transistor and the shunt resistor, wherein the failure detection unit detects a battery short of the low side output terminal, the low side ground short and the load open, and the ground open The detection unit may detect the opening of the low side ground.

In this case, the ground open detection unit includes a ground open fault diagnosis resistor connected to the shunt resistor; A ground open signal transmission unit connected to the ground open fault diagnosis resistance and the control unit; A switch connected to the ground open signal transmission unit; And a power source connected to the switch.

In addition, the power source includes a pull-up current source, and the ground open detection unit is based on the potential of the ground open sensing node between the ground open failure diagnosis resistance and the ground open signal transmission unit whether a ground open failure occurs. A signal indicative of may be generated and output to the controller.

In addition, the ground open signal transmitting unit may include a comparator that compares a potential and a reference voltage of the ground open sensing node.

In addition, the reference voltage may be configured to be set differently according to the voltage of the back-to-back diode that changes according to the temperature inside the low-side driving IC.

In addition, the voltage flowing through the ground open sensing node may be a value obtained by adding the voltage value flowing through the back-to-back diode and the voltage flowing through the shunt resistor and the ground open fault diagnosis resistor.

In addition, the voltage value of the shunt resistor and the ground open fault diagnostic resistor may be a value obtained by multiplying the resistance value of the shunt resistor and the resistance value of the ground open fault diagnostic resistor and the current value of the pull-down current source, respectively.

In addition, the comparator may be configured to transmit a ground open fault signal and an interrupt signal to the control unit when the potential of the ground open sensing node is greater than the reference voltage.

In addition, the comparator may be configured to apply a high signal to the control unit when the ground open failure occurs, and to apply a low signal to the control unit when the ground open failure does not occur.

In addition, when the ground open fault signal and the interrupt signal are applied through the comparator, the control unit may apply a control signal to turn off the load driving transistor to the load driving driver.

In addition, the control unit may control the operation of the ground opening detection unit by turning the switch on or off.

In addition, a current sensing unit connected between the load driving transistor and the shunt resistor to sense a current flowing through the shunt resistor may be further included.

On the other hand, the low-side driving IC fault diagnosis method according to an embodiment of the present invention, in the low-side IC fault diagnosis method using a low-side driving IC, applying power to the low-side driving IC, and executing a self-diagnostic mode ; Applying power to the ground opening detection unit; Comparing a voltage of a ground open sensing node and a reference voltage in the ground open detection unit; And determining whether the ground opening failure is based on the comparison value.

In this case, the ground open detection unit includes a ground open fault diagnosis resistor connected to the shunt resistor; A ground open signal transmission unit connected to the ground open fault diagnosis resistance and the control unit; A switch connected to the ground open signal transmission unit; And a power source connected to the switch, wherein the comparing step includes: a signal indicating whether a ground open failure occurs based on a potential of a ground open sensing node between the ground open failure diagnosis resistance and the ground open signal transmission unit. It can be generated and output to the control unit.

In addition, after the step of determining whether the ground is open, exiting the self-diagnosis mode and entering a normal operation mode; further comprising, when determining as the ground open failure in the determining whether the ground is open, the After the normal mode entry step, the ground open fault signal and the interrupt signal may be applied to the controller.

In addition, the control unit may be controlled to receive the ground open fault signal and the interrupt signal, and apply a control signal to turn off the load driving transistor to the load driving driver so that the normal operation mode cannot be performed. have.

In addition, if it is determined that the ground is not an open fault in the determining whether the ground is open, the controller may control to perform the normal operation mode.

A low-side driving IC failure diagnosis apparatus and method according to an embodiment of the present invention made as described above is a semiconductor and a controller generated due to a ground open failure by detecting a failure in the case where the ground of the low-side driving IC output terminal is opened Malfunctions, semiconductor destruction, and the like can be prevented. Of course, the scope of the present invention is not limited by these effects.

1 is a circuit diagram of a low-side driving IC fault diagnosis apparatus according to an embodiment of the present invention.
2 is a view for explaining the operation of the ground opening detection unit according to an embodiment of the present invention.
3 is a flowchart illustrating a low-side driving IC failure diagnosis method according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and the following embodiments make the disclosure of the present invention complete, and the scope of the invention to those skilled in the art It is provided to inform you completely. In addition, for convenience of description, in the drawings, the size of components may be exaggerated or reduced. In addition, the following embodiments are provided to those of ordinary skill in the art to fully understand the present invention and may be modified in various other forms, and the scope of the present invention is limited to the embodiments described below. It does not work.

1 is a circuit diagram of a low-side driving IC fault diagnosis apparatus according to an embodiment of the present invention.

1, the low-side driving IC fault diagnosis apparatus 110 according to an embodiment of the present invention includes a control unit 130, a load driving transistor 113, a load driving driver 111, a shunt resistor 143, It may include a current detection unit 117, a failure detection unit 115, a back-to-back (back-to-back) diode 140 and the ground open detection unit 120.

The control unit 130 performs overall control of the low-side driving IC 110 and may apply a driving signal for driving the load driving transistor 113 to the load driving driver 111.

The load driving transistor 113 is a switch for driving the load 100, and is typically implemented as a MOSFET. However, a person skilled in the art can appropriately implement the load driving transistor 113 as a bipolar transistor or IGBT depending on the situation.

The load driving driver 111 is connected to the load driving transistor 113 and, in more detail, connected to the gate of the load driving transistor 113. The load driving driver 111 may control the load driving transistor 113 to be turned on or off by supplying a voltage to the load driving transistor 113 under the control of the control unit 130, wherein the load driving transistor 113 is turned on or off. ) Is turned on, the load 100 is operated by receiving current from a power source (VBAT).

Since the shunt resistor 143 is connected between the load driving transistor 113 and the low side ground (PGND, 150) and is connected in series with the load 100, the current flowing through the load 100 is applied to the shunt resistor 143. It flows the same as the current that flows.

The current sensing unit 117 may detect whether or not an overcurrent flows through the load 100 by sensing the current flowing through the shunt resistor 143.

The current sensing unit 117 may be configured as, for example, a comparator, and compare a current flowing through the shunt resistor 143 with a reference current for determining an overcurrent and input a signal related to the overcurrent to the controller 130. .

The failure detection unit 115 is based on the potential of both ends of the shunt resistor 143 that changes as the load driving transistor 113 is turned on or off, a short circuit to the short circuit to the output terminal of the low side IC 110 (SCB) Faults such as Battery, Short Circuit to Ground (SCG) and Open load (OL) can be detected.

The back-to-back diode (140) is connected between the low-side ground (PGND, 150) and another domain ground (GND, 160) connected to another power domain and the shunt resistor (143), and the back-to-back diode (140) ) Includes a first diode 141 and a second diode 142, and the first diode 141 and the second diode 142 are connected in parallel to each other.

For example, in general, the driver IC circuit structure has separate high-current / high-voltage circuit regions and low-current / low-voltage circuit regions, and each circuit region uses independent power domains. In this case, a back-to-back diode 140 ) To adjust the ground potential difference between the high current / high voltage circuit region and the low current / low voltage circuit region.

On the other hand, the present invention, in addition to the battery short circuit (SCB), ground short circuit (SCG) and load open (OL) of the low-side driving IC 110 output terminal through the fault detection unit 115, the ground of the low-side driving IC 110 output terminal In order to further detect an open (OG) fault, a low-side ground open (OG) fault may be further detected through the ground open detector 120.

The ground open detection unit 120 may include a pull-up current source 123, a switch 125, a ground open detection resistor 129, and a ground open signal transmission unit 127, and the ground open detection unit 120 ) Is connected between the load driving transistor 113 and the shunt resistor 143.

The pull-up current source 123 is connected to the switch 125 and may receive power VDD.

On the other hand, the present invention can reduce the amount of current flowing through the ground opening detection unit 120 using the pull-up current source 123, in this case, the current size can be reduced by using a resistor instead of the pull-up current source 123, but the ground is open. In order to reduce the amount of current flowing through the detector 120, a large resistor should be used, and if a large resistor is used, a space limitation in the circuit may occur. Therefore, using a relatively small pull-up current source 123 uses a large resistor. It is more efficient than that.

For example, the pull-up current source 123 used in the ground open detection unit 120 of the low-side driving IC failure diagnosis device 110 of the present invention may be omitted.

The switch 125 is connected between the pull-up current source 123 and the ground open fault diagnosis resistor 129, and may be turned on or off under the control of the controller 13.

At this time, the control unit 130 may turn on the switch 125 to detect a ground open failure of the output terminal of the low side driving IC 110, or turn off the switch 125 when not detecting a low side ground open failure. I can do it.

That is, the controller 130 may turn on or off the switch 125 to diagnose the ground open detection failure of the output terminal of the low-side driving IC 110.

The ground open fault diagnosis resistor 129 of the ground open detection unit 120 is connected between the shunt resistor 143 and the ground open signal transmission unit 127.

The ground open signal transmission unit 127 is connected between the switch 125 and the control unit 130, and may include a comparator that compares the potential of the ground open sensing node 128 and the reference voltage V _{TH_OG} .

In addition, the ground open signal transmitting unit 127 may compare the potential of the ground open sensing node 128 and the reference voltage V _{TH_OG} to input a signal related to a low side ground open failure to the controller 130.

When the potential of the ground open sensing node 128 is greater than the reference voltage V _{TH_OG} , the ground open signal transmitting unit 127 may apply a low side ground open fault signal and an interrupt signal to the controller 130. have.

More specifically, the detection of the ground open failure of the low-side driving IC output terminal will be described later in detail with reference to FIG. 2.

2 is a view for explaining the operation of the ground opening detection unit according to an embodiment of the present invention.

Referring to FIG. 2, when the control unit 130 first turns on the switch 125 to detect the ground opening of the output terminal of the low-side driving IC 110, power VDD may be applied to the ground opening detection unit 120. .

At this time, when the power supply (VDD) is applied to the ground opening detection unit 120, a current flows to the ground opening detection unit 120, and the current is a switch 125 from the pull-up current source 123, a ground opening failure diagnosis resistance 129 ), The shunt resistor 143 and the first diode (V _D , 141).

The ground open detection unit 120 generates a signal indicating whether a low-side ground open failure occurs based on the potential of the ground open sensing node 128 between the ground open failure diagnosis resistor 129 and the ground open signal transmission unit 127 It can be output to the control unit 130.

More specifically, the ground open signal transmitting unit 127 may compare the potential of the ground open sensing node 128 and the reference voltage V _{TH_OG} to output a signal regarding whether the low side ground is open to the control unit 130. have.

In this case, the reference voltage V _{TH_OG} applied to the ground open signal transmission unit 127 may be set differently according to the voltage of the back-to-back diode 140 that changes according to the temperature inside the low-side driving IC 110.

For example, the back-to-back diode 140 has a voltage value of 0.7 V at room temperature, and when the temperature is high, the voltage may decrease to a voltage value of 0.3 V. Therefore, the reference voltage (V _{TH_OG} ) applied to the ground open signal transmitting unit 127 to detect an accurate ground open failure is based on the voltage of the back-to-back diode 140 that changes according to the temperature inside the low-side driving IC 110. It can be set differently accordingly.

The voltage flowing through the ground open sensing node 128 is a value obtained by adding the voltage flowing through the back-to-back diode 140 and the voltage flowing through the shunt resistor 143 and the ground open failure diagnosis resistor 129.

Here, the voltage values of the shunt resistor 143 and the ground open fault diagnostic resistor 129 are the resistance values of the shunt resistor 143 and the resistance value of the ground open fault diagnostic resistor 129 and the current of the pull-up current source I _SOURCE , 123 It is the value multiplied by each.

Meanwhile, when the potential of the ground open fault sensing node 128 is greater than the reference voltage (V _{TH_OG} ), the ground open signal transmitting unit 127 opens the low side ground to the controller 130. A fault signal and an interrupt signal can be applied, and expressed as Equation 1 below.

Here, V _{TH_OG} is the reference voltage, V _D is the voltage of the first diode 141, R _S is the resistance value of the ground open fault diagnosis resistor 129, R _SHUNT is the resistance value of the shunt resistor 143, I _SOURCE is It is the current value of the pull-up current source 123.

As described above, when the ground open signal transmitting unit 127 compares the potential of the ground open sensing node 128 and the reference voltage V _{TH_OG} , the potential of the ground open sensing node 128 is greater than the reference voltage V _{TH_OG} . The ground open signal transmission unit 127 may apply a low side ground open fault signal to the controller 130.

In more detail, the ground open signal transmitting unit 127 may input a HIGH signal to the controller 130 when the potential of the ground open sensing node 127 is greater than the reference voltage V _{TH_OG} , and the ground open sensing node 128 When the potential of) is less than the reference voltage V _{TH_OG} , a LOW signal may be input to the controller 130.

3 is a flowchart of a low-side driving IC failure diagnosis method according to an embodiment of the present invention.

Referring to FIG. 3, first, a power supply VBAT is applied to the low-side driving IC 110 and may enter a power-up mode. (Step S300)

Here, the power-up mode is a state in which a current flows through the low-side driving IC 110 while a power supply VBAT is applied to the low-side driving IC 110.

At this time, power (VBAT) is applied to the low-side driving IC 110, and the low-side driving IC 110 may enter a built-in self test mode (BIST). (Step S310)

When the self-diagnosis mode (BIST) is performed in the low-side driving IC 110, the ground-opening detection unit 120 may be operated to detect a ground (PGND, 150) open failure of the output of the low-side driving IC 110. . (Step S320)

In more detail, in order to operate the ground open detection unit 120, the control unit 130 of the low side driving IC 110 may turn on the switch 125 of the ground open detection unit 120, and the ground open detection unit 120 may be turned on. When the switch 125 is turned on, the ground open detection unit 120 may be operated while power VDD is applied to the ground open detection unit 120.

Meanwhile, as the ground open detection unit 120 is operated, the ground open detection unit 120 may check whether a ground open failure has occurred at the output terminal of the low side driving IC 110. (Step S330)

When the ground open detection unit 120 is operated, a current flows through the ground open detection unit 120, and the potential and reference voltage of the ground open sensing node 128 in the ground open signal transmission unit 127 of the ground open detection unit 120 ( V _{TH_OG} ) may be compared to input a signal regarding whether the low side ground is open or not.

At this time, when the potential of the ground open sensing node 128 in the ground open signal transmitting unit 127 is greater than the reference voltage V _{TH_OG} , the control unit 130 controls a signal indicating that a low side ground open failure has occurred and an interrupt signal. ), And when the potential of the ground open sensing node 128 is lower than the reference voltage V _{TH_OG} , a signal that the low side ground open failure has not occurred may be applied to the controller 130.

For example, the ground open signal transmitting unit 127 may apply a HIGH signal to the control unit 130 when a low side ground opening occurs, and a low signal to the control unit 130 when a low side ground opening does not occur. Can apply.

On the other hand, when a low side ground open failure does not occur or when a low side ground open failure occurs, the self-diagnosis mode of the low side driving IC may be terminated and the normal operation mode may be entered. (Step S340)

Here, entering the normal operation mode refers to a step immediately before executing the normal operation mode, rather than executing the normal operation mode. In addition, regardless of whether a low-side ground opening failure occurs, the low-side driving IC failure diagnosis device 110 detects the ground opening of the low-side driving IC 110 output terminal, terminates the self-diagnosis mode, and enters a normal operation mode. However, if a ground open failure of the output terminal of the low-side driving IC 110 does not occur, the normal operation mode may be performed while entering the normal operation mode.

When a ground open failure of the output side of the low-side driving IC 110 occurs, the system enters a normal mode, but the ground open signal transmission unit 127 inputs a ground open failure signal and an interrupt signal to the control unit 130 Then, the control unit 130 receiving the interrupt signal may control the load driving transistor 113. (Step S350)

In more detail, the controller 130 applies a driving signal to the load driving driver 111 so that the load driving transistor 113 is turned off, and the load driving driver 111 turns the load driving transistor 113 off. Can be switched.

For example, when a ground open failure occurs in the output terminal of the low-side driving IC 110, a large current flows in the low-side driving IC 110, and the circuit configuration is unreasonable, and a problem may occur in driving the load 100. Therefore, it is possible to control the load driving transistor 113 to be turned off so that the load 100 is not driven.

Meanwhile, a battery short circuit (SCB), a ground short circuit (SCG), and a load open (OL) failure of the low-side driving IC output terminal based on a potential difference between shunt resistors according to turn-on or turn-off of a load driving transistor through a failure detection unit in the related art Bay was detected, and ground opening of the low-side driving IC output was not detected.

However, since the present invention can additionally detect a ground opening failure of the low-side driving IC output terminal through the ground opening detection unit 120, when an actual ground opening occurs, semiconductor and controller malfunctions, semiconductor destruction, and the like can be prevented. have.

In the detailed description and the accompanying drawings, specific embodiments have been described, but the present invention is not limited to the disclosed embodiments and does not depart from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. Various substitutions, modifications and changes are possible within the scope. Therefore, the scope of the present invention should be construed as being limited to the described embodiments, and should be interpreted as including the claims and equivalents as well as the claims described later.

100: load
120: ground opening detection unit
123: pull-up current source
125: switch
129: Ground open fault diagnosis resistance
127: ground open signal transmission unit
130: control unit
140: back-to-back diode
143: Shunt resistance
150: ground

Claims (17)

A load driving transistor for driving a load connected between the battery and the low side output terminal;
A load driving driver for controlling the load driving transistor;
A control unit connected to the load driving driver and applying a driving signal for driving the load driving transistor to the load driving driver;
A shunt resistor connected in series between the load and the low side ground;
A back-to-back diode connected between the low-side ground and another shunt resistor connected to another power domain-in ground;
A fault detector for detecting a fault based on a potential across the shunt resistor that changes as the load driving transistor is turned on or off; And
And a ground open detection unit connected between the load driving transistor and the shunt resistor.
The failure detection unit detects a short circuit in the battery of the low side output terminal, the low side ground short circuit, and the load open,
The ground opening detection unit detects the opening of the low side ground,
Low side driving IC.
According to claim 1,
The ground opening detection unit,
A ground open fault diagnosis resistor connected to the shunt resistor;
A ground open signal transmission unit connected to the ground open fault diagnosis resistance and the control unit;
A switch connected to the ground open signal transmission unit; And
Power supply connected to the switch; including,
Low side driving IC.
According to claim 2,
The power source includes a pull-up current source,
The ground opening detection unit,
Generating a signal indicating whether a ground open failure is based on the potential of the ground open sensing node between the ground open failure diagnosis resistance and the ground open signal transmission unit, and outputs a signal to the control unit,
Low side driving IC.
The method of claim 3,
The ground open signal transmission unit includes a comparator that compares the potential of the ground open sensing node with a reference voltage,
Low side driving IC.
The method of claim 4,
The reference voltage is configured to be set differently according to the voltage of the back-to-back diode that changes according to the temperature inside the low-side driving IC,
Low side driving IC.
The method of claim 4,
The voltage flowing through the ground open sensing node is a value obtained by adding the voltage value flowing through the back-to-back diode and the voltage flowing through the shunt resistor and the ground open fault diagnosis resistor.
Low side driving IC.
The method of claim 6,
The voltage value of the shunt resistor and the ground open fault diagnostic resistor is a value obtained by multiplying the resistance value of the shunt resistor and the resistance value of the ground open fault diagnostic resistor and the current value of the pull-up current source, respectively.
Low side driving IC.
The method of claim 4,
The comparator is configured to transmit a ground open fault signal and an interrupt signal to the control unit when the potential of the ground open sensing node is greater than the reference voltage,
Low side driving IC.
The method of claim 8,
The comparator is configured to apply a high signal to the control unit when the ground open failure occurs, and to apply a low signal to the control unit when the ground open failure does not occur,
Low side driving IC.
The method of claim 8,
When the ground open fault signal and the interrupt signal are applied through the comparator, the control unit applies a control signal to turn off the load driving transistor to the load driving driver.
Low side driving IC.
According to claim 2,
The control unit controls the operation of the ground opening detection unit by turning on or off the switch,
Low side driving IC.
According to claim 2,
Further comprising a current sensing unit connected between the load driving transistor and the shunt resistor to sense the current flowing through the shunt resistor,
Low side driving IC.
In the low-side IC fault diagnosis method using the low-side driving IC of claim 1,
Applying power to the low-side driving IC and executing a self-diagnosis mode;
Applying power to the ground opening detection unit;
Comparing a voltage of a ground open sensing node and a reference voltage in the ground open detection unit; And
Including the ground opening failure based on the comparison value; includes,
Low side driving IC fault diagnosis method.
The method of claim 13,
The ground opening detection unit,
A ground open fault diagnosis resistor connected to the shunt resistor;
A ground open signal transmission unit connected to the ground open fault diagnosis resistance and the control unit;
A switch connected to the ground open signal transmission unit; And
It includes; a power source connected to the switch;
The comparing step,
Generating a signal indicating whether a ground open failure is based on the potential of the ground open sensing node between the ground open failure diagnosis resistance and the ground open signal transmission unit, and outputs a signal to the control unit,
Low side driving IC fault diagnosis method.
The method of claim 13,
After the ground open failure determination step,
Further comprising the step of exiting the self-diagnosis mode and entering the normal operation mode,
If it is determined that the ground open failure occurs in the ground open failure determination step, applying a ground open failure signal and an interrupt signal to the control unit after the step of entering the normal operation mode,
Low side driving IC fault diagnosis method.
The method of claim 15,
The control unit receives the ground open fault signal and the interrupt signal and applies a control signal to turn off the load driving transistor to the load driving driver to control the normal operation mode from being performed.
Low side driving IC fault diagnosis method.
The method of claim 15,
If it is determined in the step of determining whether the ground is open, the ground is not open, the control unit controls to perform the normal operation mode.
Low side driving IC fault diagnosis method.

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