CAN bus transceiver interface circuit with intelligent fault diagnosis function

Abstract

This invention discloses a CAN bus transceiver interface circuit with intelligent fault diagnosis function, including a CAN bus transceiver, a microcontroller unit, a CAN bus protection module, a CAN bus status monitoring module, and a fault indication module. The CAN bus transceiver is electrically connected to the microcontroller unit, the CAN bus protection module is connected in series between the transceiver and the CAN bus, the status monitoring module collects differential voltage and single-line absolute voltage, the microcontroller unit identifies various physical layer faults through a fault diagnosis algorithm, and the fault indication module issues an alarm. This circuit solves the problems of passive and untimely fault diagnosis in traditional CAN bus interface circuits, realizing real-time proactive diagnosis of physical layer faults, simplifying fault troubleshooting, and enhancing the reliability of in-vehicle CAN communication and vehicle operation safety.

Description

Technical Field

[0001] This invention relates to the field of vehicle electronic equipment technology, and more specifically to a CAN bus transceiver interface circuit with intelligent fault diagnosis function. Background Technology

[0002] As the core communication protocol of automotive electronic systems, the CAN bus undertakes the data transmission tasks between various electronic control units, and its communication stability directly determines the vehicle's operating status. In the vehicle environment, factors such as electromagnetic interference, power fluctuations, and wire wear can easily cause physical layer faults such as open circuits and short circuits in the CAN bus. Existing CAN bus interface circuits only focus on signal transmission and reception, lacking an active monitoring mechanism. They can only passively detect problems when communication is completely interrupted or a large number of error frames occur, and cannot identify the fault type in real time. This results in time-consuming fault location, low maintenance efficiency, and may even lead to vehicle operational safety hazards due to the escalation of the fault.

[0003] Based on the above problems, there is an urgent need for an interface circuit that can actively and in real time monitor the bus status and accurately identify the fault type, so as to solve the core problems of lagging fault diagnosis and difficult troubleshooting in traditional solutions. Summary of the Invention

[0004] The purpose of this invention is to provide a CAN bus transceiver interface circuit with intelligent fault diagnosis function, including a CAN bus transceiver, a microcontroller unit, a CAN bus protection module, a CAN bus status monitoring module, and a fault indication module. The CAN-TX and CAN-RX pins of the CAN bus transceiver are electrically connected to the microcontroller unit, and the CAN-H and CAN-L pins of the CAN bus transceiver are used to connect to the CAN bus. The CAN bus protection module is connected in series between the CAN bus transceiver and the CAN bus to suppress common-mode noise and absorb transient high voltage. The CAN bus status monitoring module is used to collect in real time the differential voltage between the CAN-H and CAN-L pins, the absolute voltage level of the CAN-H pin relative to ground, and the absolute voltage level of the CAN-L pin relative to ground. The microcontroller unit has a built-in fault diagnosis algorithm to receive the data collected by the CAN bus status monitoring module and identify CAN-H open circuit, CAN-L open circuit, CAN-H short circuit to ground, CAN-L short circuit to power supply, CAN-H and CAN-L short circuit, and transceiver faults based on the collected data. The fault indication module is electrically connected to the microcontroller unit to receive fault signals output by the microcontroller unit and issue alarms.

[0005] Preferably, the CAN bus transceiver uses the TJA1043T chip. The CAN-H and CAN-L pins of the TJA1043T chip are electrically connected to the CAN bus protection module, and the CAN-TX and CAN-RX pins of the TJA1043T chip are electrically connected to the corresponding pins of the microcontroller unit. The TJA1043T chip has a built-in bus short-circuit protection unit and an over-temperature protection unit, and is equipped with an ERR_N pin as a fault signal output terminal.

[0006] Preferably, the microcontroller unit uses the S32K144 chip, which integrates a CAN module, an ADC module, and an error counter. The CAN1_RX pin of the CAN module is electrically connected to the CAN-RX pin of the CAN bus transceiver, and the CAN1_TX pin of the CAN module is electrically connected to the CAN-TX pin of the CAN bus transceiver. The ADC module is used to sample the absolute voltage levels of the CAN-H and CAN-L pins. The error counter is used to count the number of CAN signal transmission errors and reception errors, and the threshold of the error counter is set to 128.

[0007] More preferably, the CAN bus protection module includes a common-mode inductor and a transient voltage suppressor; the common-mode inductor is model ACT45B-510-2P-TL003, with its two input terminals electrically connected to the CAN-H and CAN-L pins of the CAN bus transceiver, respectively, and its two output terminals electrically connected to the corresponding lines of the CAN bus; the transient voltage suppressor is model PESD2IVN24-T, with its two input terminals electrically connected to the CAN-H and CAN-L pins of the CAN bus transceiver, respectively, and its output terminal grounded.

[0008] More preferably, the CAN bus status monitoring module includes a resistor divider network, a Zener diode, and a comparator. The resistor divider network consists of two resistors with a precision of 10KΩ±1%. One end of one resistor is electrically connected to the CAN-H pin, and the other end is electrically connected to the non-inverting input of the comparator. One end of the other resistor is electrically connected to the CAN-L pin, and the other end is electrically connected to the inverting input of the comparator. The Zener diode is a BZT52C5V1TQ-7-F type and is connected in parallel between the output of the resistor divider network and ground. The comparator is used to compare the output voltage of the resistor divider network with a preset threshold voltage and output a digital level signal to the microcontroller unit.

[0009] Further preferred, the fault judgment criteria of the fault diagnosis algorithm are as follows: CAN-H open circuit corresponds to CAN-L pin voltage in the range of 1.5V-3.5V and CAN-H pin voltage continuously below 0.5V or above 4.5V; CAN-L open circuit corresponds to CAN-H pin voltage in the range of 1.5V-3.5V and CAN-L pin voltage continuously below 0.5V or above 4.5V; CAN-H short circuit to ground corresponds to CAN-H pin voltage continuously below 0.5V; CAN-L short circuit to power supply corresponds to CAN-L pin voltage continuously above 4.5V; CAN-H and CAN-L short circuit corresponds to differential voltage between the two pins continuously in the range of 0V-0.5V; transceiver fault corresponds to CAN-RX pin continuously having no signal and CAN bus differential voltage within the normal range.

[0010] Further preferably, the differential voltage sampling period of the CAN bus status monitoring module is 1ms, and the normal range of the differential voltage is 2V-4V in the dominant state and 0V-1V in the recessive state; the microcontroller unit is set with a monitoring time window of 10ms-50ms, and when the differential voltage continuously exceeds the normal range within the set time window, a communication abnormality warning is triggered.

[0011] Further preferably, the fault indication module includes a fault flag pin and a CAN-INH pin; the fault flag pin is electrically connected to the ERR_N pin of the TJA1043T chip, and the CAN-INH pin is electrically connected to the CAN-INH-DET pin of the microcontroller unit through a resistor with a precision of 10KΩ±1%; after receiving a fault signal, the microcontroller unit records a 16-bit binary code fault code in its internal memory, with each fault type corresponding to a unique fault code.

[0012] Further preferred, the self-test process of the microcontroller unit is as follows: First, after power-on, the static voltage of the CAN-H pin and CAN-L pin is detected for 200ms, and no CAN message is sent during the detection period; Second, the initial value of the CAN module error counter is read. If the initial value is greater than 0, an alarm is issued through the fault indication module; Third, a test message containing 8 bytes of data is sent, and the response message is detected after 100ms. If no response is received, it is determined that the communication link is faulty.

[0013] Further preferred, the auxiliary diagnostic methods for the microcontroller unit are as follows: sending test messages at 500ms intervals, waiting 50ms for a response after each transmission, and triggering a fault diagnosis process if no response is received after 3 consecutive transmissions; sampling the single-ended levels of the CAN-H and CAN-L pins at a frequency of 10kHz using the ADC module, and processing the sampled data through a moving average filter of 5 sampling points; and receiving explicit timeout, implicit bus monitoring, over-temperature, and under-voltage diagnostic information transmitted by the TJA1043T chip through the I2C communication interface.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] The core innovation of this invention lies in integrating a dual-dimensional monitoring mechanism of differential voltage and single-line absolute voltage, combined with a built-in fault diagnosis algorithm to achieve proactive identification of physical layer faults. This design accurately solves the core problems of passive and lagging fault diagnosis in traditional CAN bus interface circuits, capturing abnormal bus status in real time, clearly distinguishing multiple fault types, significantly shortening fault troubleshooting time, and ensuring the circuit's anti-interference capability through a protection module, thus significantly improving the reliability of in-vehicle CAN communication and the safety of vehicle operation. Attached Figure Description

[0016] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0017] Figure 1 This is a block diagram of the CAN bus transceiver interface circuit with intelligent fault diagnosis function of the present invention.

[0018] Figure 2 This is a schematic diagram of the CAN bus transceiver interface circuit with intelligent fault diagnosis function of the present invention.

[0019] Figure 3 This is a circuit diagram showing the test points and pinout of the CAN bus transceiver interface circuit of this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The concepts involved in this application will first be described with reference to the accompanying drawings. It should be noted that the following descriptions of various concepts are only for the purpose of making the content of this application easier to understand and do not constitute a limitation on the scope of protection of this application; furthermore, the embodiments and features in the embodiments of this application can be combined with each other unless otherwise specified. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] Technical problems with existing technologies: Traditional CAN bus interface circuits only focus on signal transmission and reception functions, lack an active monitoring mechanism for the status of the bus physical layer, cannot synchronously collect differential voltage and single-line absolute voltage data, and have no dedicated fault diagnosis algorithm to identify specific fault types. As a result, faults can only be passively discovered and are difficult to troubleshoot, affecting the stability of vehicle communication and the safety of vehicle operation.

[0023] Based on this, please refer to Figures 1-3 This embodiment provides a CAN bus transceiver interface circuit with intelligent fault diagnosis function, including a CAN bus transceiver, a microcontroller unit, a CAN bus protection module, a CAN bus status monitoring module, and a fault indication module. The CAN-TX and CAN-RX pins of the CAN bus transceiver are electrically connected to the microcontroller unit, and the CAN-H and CAN-L pins of the CAN bus transceiver are used to connect to the CAN bus. The CAN bus protection module is connected in series between the CAN bus transceiver and the CAN bus to suppress common-mode noise and absorb transient high voltage. The CAN bus status monitoring module is used to collect the differential voltage between the CAN-H and CAN-L pins, the absolute voltage level of the CAN-H pin relative to ground, and the absolute voltage level of the CAN-L pin relative to ground in real time. The microcontroller unit has a built-in fault diagnosis algorithm to receive the data collected by the CAN bus status monitoring module and identify CAN-H open circuit, CAN-L open circuit, CAN-H short circuit to ground, CAN-L short circuit to power supply, CAN-H and CAN-L short circuit, and transceiver faults based on the collected data. The fault indication module is electrically connected to the microcontroller unit to receive the fault signal output by the microcontroller unit and issue an alarm.

[0024] It is worth mentioning that the CAN bus transceiver uses the TJA1043T chip, a dedicated transceiver for automotive CAN communication. Its CAN-TX and CAN-RX pins establish a stable electrical connection directly with the corresponding pins of the microcontroller unit via wires, ensuring reliable transmission of logic level signals. The CAN-H and CAN-L pins serve as differential signal input / output terminals, directly connecting to the CAN bus protection module to achieve physical layer conversion and driving of bus signals. The microcontroller unit uses the S32K144 chip, which integrates a high-performance CAN module, a 12-bit ADC module, and a dedicated error counter. The CAN module is responsible for data interaction with the transceiver, the ADC module is specifically used to acquire the single-line absolute voltage of CAN-H and CAN-L, and the error counter counts the number of transmission and reception errors in real time. The built-in fault diagnosis algorithm is pre-stored in the chip's flash memory. After the algorithm is started, it continuously receives two-dimensional voltage data transmitted by the CAN bus status monitoring module. By comparing the preset voltage threshold with the real-time acquired data, it accurately identifies six types of physical layer faults. The CAN bus protection module consists of a common-mode inductor and a transient voltage suppressor. The common-mode inductor is model ACT45B-510-2P-TL003, with its two inputs soldered to the CAN-H and CAN-L pins of the CAN bus transceiver, respectively, and its two outputs connected to the corresponding lines of the CAN bus. This effectively filters out common-mode interference signals on the bus and improves the anti-interference capability of differential signals. The transient voltage suppressor is model PESD2IVN24-T, with its two inputs connected to the CAN-H and CAN-L pins, respectively, and its output directly grounded. This allows it to quickly absorb transient high voltages generated by electrostatic discharge or load changes, preventing the transceiver chip from being damaged. The CAN bus status monitoring module integrates a resistor divider network, a Zener diode, and a comparator. The resistor divider network consists of two resistors with a precision of 10KΩ±1%, drawing power from the CAN-H and CAN-L pins respectively, dividing the bus voltage to a range recognizable by the comparator. The Zener diode is connected in parallel between the output of the voltage divider network and ground to ensure a stable and fluctuation-free voltage signal input to the comparator. The comparator compares the divided voltage signal with an internal preset threshold, converting the analog voltage signal into a digital level signal before transmitting it to the microcontroller unit, enabling real-time acquisition and conversion of voltage data. The fault indication module includes a fault flag pin and a CAN-INH pin. The fault flag pin is connected to the ERR_N pin of the CAN bus transceiver, and the CAN-INH pin is connected to the CAN-INH-DET pin of the microcontroller unit via a resistor. When the microcontroller unit detects a fault, it sends a fault alarm to the external system by controlling the level states of these two pins.Each module establishes a data connection through wires or a dedicated bus, forming a complete closed loop of "signal transmission and reception - status monitoring - fault diagnosis - alarm output", ensuring comprehensive monitoring and rapid response to the physical layer status of the CAN bus.

[0025] Technical effects achieved: Real-time proactive diagnosis of CAN bus physical layer faults, accurate identification of various fault types, simplification of fault diagnosis process, and improvement of vehicle CAN communication reliability and vehicle operation safety.

[0026] Technical problems with existing technologies: Ordinary CAN bus transceivers lack a dedicated fault signal output interface and have no built-in protection unit, making it impossible to directly feedback the fault status. They are easily damaged by bus anomalies, resulting in delayed fault diagnosis response and affecting the stability of the entire interface circuit.

[0027] Based on this, the CAN bus transceiver uses the TJA1043T chip. The CAN-H and CAN-L pins of the TJA1043T chip are electrically connected to the CAN bus protection module, and the CAN-TX and CAN-RX pins of the TJA1043T chip are electrically connected to the corresponding pins of the microcontroller unit. The TJA1043T chip has a built-in bus short-circuit protection unit and an over-temperature protection unit, and it also has an ERR_N pin as a fault signal output terminal.

[0028] It's worth noting that the TJA1043T chip is a high-reliability transceiver specifically designed for automotive CAN communication. Its CAN-H and CAN-L pins employ a differential drive structure, enabling the output of differential voltage signals conforming to the CAN protocol specifications. These pins establish a low-impedance connection with the common-mode inductor input of the CAN bus protection module via gold-plated pads, reducing signal transmission loss. The CAN-TX and CAN-RX pins are logic-level interfaces, directly connected to their corresponding pins in the microcontroller unit via a point-to-point connection, supporting a maximum transmission rate of 1Mbps to meet the real-time requirements of automotive communication. The chip's built-in bus short-circuit protection unit detects current changes on the CAN-H and CAN-L pins. When a short circuit is detected causing the current to exceed a safe threshold, the output drive is automatically cut off to prevent the internal power transistors from burning out. The over-temperature protection unit monitors the chip's junction temperature in real time using a built-in temperature sensor. When the junction temperature exceeds 150°C, a protection mechanism is triggered to reduce the chip's power consumption until the temperature returns to a safe range. The ERR_N pin is a dedicated fault signal output terminal for the chip. Under normal operating conditions, it remains high. When the chip detects abnormal conditions such as bus short circuits, over-temperature, or under-voltage, this pin is immediately pulled low, directly outputting a fault signal to the microcontroller unit without a complex signal conversion process, ensuring the timeliness and accuracy of fault signal transmission. The chip's power supply pin is connected to the automotive power supply via decoupling capacitors, reducing the impact of power fluctuations on chip operation and enabling the chip to operate stably within a wide input voltage range of 10V-28V, adapting to the voltage fluctuation characteristics of automotive power supplies.

[0029] Technical effects achieved: The built-in protection unit enhances the transceiver's anti-interference and anti-damage capabilities, and the dedicated fault output pin enables rapid feedback of fault signals, ensuring the overall stability of the interface circuit and the real-time fault diagnosis.

[0030] Technical problems with existing technologies: Ordinary microcontrollers lack integrated CAN modules, ADC modules and error counters, requiring multiple external dedicated chips to achieve the corresponding functions, resulting in complex circuit structures, large data transmission delays, and an inability to meet the computing power requirements of fault diagnosis algorithms for multi-module collaborative operation.

[0031] Based on this, the microcontroller unit uses the S32K144 chip, which integrates a CAN module, an ADC module, and an error counter. The CAN1_RX pin of the CAN module is electrically connected to the CAN-RX pin of the CAN bus transceiver, and the CAN1_TX pin of the CAN module is electrically connected to the CAN-TX pin of the CAN bus transceiver. The ADC module is used to sample the absolute voltage levels of the CAN-H and CAN-L pins. The error counter is used to count the number of CAN signal transmission errors and reception errors, and the threshold of the error counter is set to 128.

[0032] It's worth noting that the S32K144 chip is a high-performance microcontroller designed for automotive applications. Its built-in CAN module conforms to the CAN 2.0A / B protocol specifications, supporting standard and extended frame transmission. The CAN1_RX and CAN1_TX pins employ a differential input / output structure, connected to the corresponding pins of the CAN bus transceiver via shielded wires to reduce the impact of electromagnetic interference on signal transmission. The ADC module is a 12-bit successive approximation analog-to-digital converter with multi-channel sampling capability. Two channels are dedicated to acquiring the absolute voltage levels of the CAN-H and CAN-L pins, with a sampling rate up to 1MHz, enabling rapid capture of dynamic changes in bus voltage. The ADC module incorporates a sample-and-hold circuit and a reference voltage source, ensuring that the accuracy error of the sampled data does not exceed ±1LSB. Error counters include a transmit error counter and a receive error counter, operating independently to count error events during CAN signal transmission and reception. Error events include bit errors, stuffing errors, and CRC errors. When the value of either counter reaches 128, the chip automatically triggers an interrupt signal, notifying the fault diagnosis algorithm to initiate the fault investigation process. The chip's central processing unit uses an ARM Cortex-M4 core with a maximum operating frequency of 112MHz. It has powerful digital signal processing capabilities, enabling efficient operation of fault diagnosis algorithms and real-time analysis of voltage data and identification of fault types. The chip has a built-in flash memory capacity of up to 1MB and a RAM capacity of up to 128KB, providing ample memory space for the storage and operation of fault diagnosis algorithms. The chip also supports multiple communication interfaces such as SPI and I2C, facilitating data interaction with other modules and enabling multi-module collaborative work.

[0033] Technical effects achieved: The integrated modular design simplifies the circuit structure, improves data transmission rate and processing efficiency, meets the requirements of fault diagnosis for computing power and sampling accuracy, and ensures the accuracy and real-time performance of fault identification.

[0034] Technical problems with existing technologies: Traditional CAN bus protection circuits use only a single protection element, which cannot simultaneously suppress common-mode noise and transient high voltage, resulting in limited protection effects. This makes CAN bus transceivers susceptible to damage from harsh vehicle environments, affecting communication stability.

[0035] Based on this, the CAN bus protection module includes a common-mode inductor and a transient voltage suppressor. The common-mode inductor is model ACT45B-510-2P-TL003. The two input terminals of the common-mode inductor are electrically connected to the CAN-H pin and CAN-L pin of the CAN bus transceiver, respectively, and the two output terminals of the common-mode inductor are electrically connected to the corresponding lines of the CAN bus. The transient voltage suppressor is model PESD2IVN24-T. The two input terminals of the transient voltage suppressor are electrically connected to the CAN-H pin and CAN-L pin of the CAN bus transceiver, respectively, and the output terminal of the transient voltage suppressor is grounded.

[0036] It is worth mentioning that the ACT45B-510-2P-TL003 common-mode inductor has an inductance of 510μH and a rated current of 2A, which can effectively suppress common-mode interference signals in the frequency range of 10kHz-100MHz. Its magnetic core uses high-permeability ferrite material, which has the characteristics of low loss and high saturation magnetic flux density. While suppressing interference, it will not cause significant attenuation of the differential signal of the CAN bus. The pins of the common-mode inductor are gold-plated, which can form a stable electrical connection when soldered on the PCB board and reduce contact resistance. The PESD2IVN24-T transient voltage suppressor has a breakdown voltage of 24V, a clamping voltage of 33V, and a peak pulse current of up to 3A. It can quickly respond to and absorb transient interference such as electrostatic discharge and surge voltage, with a response time of less than 1ns. This device employs a bidirectional protection structure, simultaneously protecting the CAN-H and CAN-L pins from positive and negative transient voltage impacts. The device is packaged in SOT-23, making it compact and easy to place on a PCB, with excellent heat dissipation and the ability to withstand multiple transient voltage impacts without damage. The common-mode inductor and transient voltage suppressor are placed on the PCB according to the principle of "close to the transceiver." The common-mode inductor is directly adjacent to the CAN-H and CAN-L pins of the CAN bus transceiver, and the transient voltage suppressor is connected in parallel on the line between the common-mode inductor and the transceiver, forming a protection link of "transceiver-transient voltage suppressor-common-mode inductor-bus." This ensures that the bus signal undergoes double protection before entering the transceiver, minimizing the impact of interference on the transceiver.

[0037] The achieved technical effects are: the dual protection structure simultaneously suppresses common-mode noise and transient high voltage, improves the interface circuit's ability to withstand harsh environments, effectively protects the CAN bus transceiver, and ensures stable and reliable CAN communication.

[0038] Technical problems with existing technologies: CAN bus voltage monitoring circuits are susceptible to voltage fluctuations, have insufficient accuracy in sampling data, and lack voltage stabilization mechanisms, leading to deviations in monitoring results and affecting the accuracy of fault diagnosis algorithms.

[0039] Based on this, the CAN bus status monitoring module includes a resistor divider network, a Zener diode, and a comparator. The resistor divider network consists of two resistors with a precision of 10KΩ±1%. One end of one resistor is electrically connected to the CAN-H pin, and the other end is electrically connected to the non-inverting input of the comparator. One end of the other resistor is electrically connected to the CAN-L pin, and the other end is electrically connected to the inverting input of the comparator. The Zener diode is a BZT52C5V1TQ-7-F model, connected in parallel between the output of the resistor divider network and ground. The comparator is used to compare the output voltage of the resistor divider network with a preset threshold voltage and output a digital level signal to the microcontroller unit.

[0040] It is worth mentioning that the two 10KΩ resistors used in the resistor divider network are metal film resistors with an accuracy class of ±1% and a temperature coefficient of ±50ppm / ℃. They can maintain a stable resistance value within a wide temperature range of -40℃ to 85℃ in the automotive environment, ensuring the accuracy of the voltage division ratio. One end of one resistor is connected to the CAN-H pin by soldering, and the other end is directly connected to the non-inverting input of the comparator. One end of the other resistor is soldered to the CAN-L pin, and the other end is connected to the inverting input of the comparator. The common terminal of the two resistors is grounded, forming a symmetrical voltage divider structure that can simultaneously acquire the voltage signals of CAN-H and CAN-L and convert them into low-voltage signals that the comparator can process. The BZT52C5V1TQ-7-F Zener diode has a Zener voltage of 5.1V, a maximum operating current of 200mA, a dynamic resistance of less than 5Ω, and a fast voltage regulation response. Connected in parallel between the output of the resistor divider network and ground, when the voltage after voltage division exceeds 5.1V, the diode will conduct to shunt current, clamping the output voltage to 5.1V to prevent damage to the comparator due to excessive voltage. The diode uses an SOD-123 package, which is compact, has good heat dissipation, and is suitable for placement on high-density PCBs. The comparator is a high-speed voltage comparator with a response time of less than 10ns, enabling rapid capture of voltage signal changes. The non-inverting and inverting inputs of the comparator receive voltage divider signals from CAN-H and CAN-L, respectively. The internally preset threshold voltage is set based on the CAN protocol specification: 2V in dominant mode and 1V in recessive mode. When the input voltage is higher than the threshold voltage, the comparator outputs a high level; when it is lower, it outputs a low level. The output digital signal is directly transmitted to the GPIO pins of the microcontroller unit via signal lines, providing real-time voltage status data for the fault diagnosis algorithm. The entire monitoring module is powered by a stable 3.3V voltage provided by the microcontroller unit, ensuring stable module operation and further improving the accuracy of voltage sampling.

[0041] Technical effects achieved: Through voltage regulation and precise voltage division design, the accuracy and stability of CAN bus voltage monitoring data are improved, providing reliable data support for fault diagnosis algorithms and ensuring the accuracy of fault type identification.

[0042] Technical problems with existing technologies: Fault diagnosis lacks clear and unified judgment standards, and the voltage characteristics of different fault types are vaguely defined, leading to misjudgment or omission of faults and affecting the reliability of fault diagnosis.

[0043] Based on this, the fault judgment criteria of the fault diagnosis algorithm are as follows: CAN-H open circuit corresponds to CAN-L pin voltage in the range of 1.5V-3.5V and CAN-H pin voltage continuously below 0.5V or above 4.5V; CAN-L open circuit corresponds to CAN-H pin voltage in the range of 1.5V-3.5V and CAN-L pin voltage continuously below 0.5V or above 4.5V; CAN-H short circuit to ground corresponds to CAN-H pin voltage continuously below 0.5V; CAN-L short circuit to power supply corresponds to CAN-L pin voltage continuously above 4.5V; CAN-H and CAN-L short circuit corresponds to differential voltage between the two pins continuously in the range of 0V-0.5V; transceiver fault corresponds to CAN-RX pin continuously having no signal and CAN bus differential voltage within the normal range.

[0044] It's worth noting that the fault diagnosis algorithm's judgment criteria are based on the CAN protocol specification and the electrical characteristics of the vehicle's CAN bus. All voltage ranges have undergone extensive experimental verification to ensure high recognition accuracy even under the influence of temperature and voltage fluctuations in the vehicle environment. The normal range of 1.5V-3.5V for the CAN-L pin voltage is determined based on the common-mode voltage in the recessive state of the CAN bus. When the CAN-H pin voltage is consistently below 0.5V or above 4.5V, it indicates an open circuit fault in the CAN-H line, preventing normal transmission of differential signals. Similarly, if the CAN-H pin voltage is within the normal range while the CAN-L pin voltage exceeds the 0.5V-4.5V range, it is determined to be a CAN-L open circuit. When CAN-H is short-circuited to ground, its voltage will be pulled down to near ground potential; therefore, a sustained value below 0.5V is set as the judgment criterion. When CAN-L is short-circuited to the power supply, its voltage will be pulled up to near the vehicle's power supply voltage; therefore, a sustained value above 4.5V is set as the judgment criterion. When CAN-H and CAN-L are working normally, the differential voltage is 2V-4V in the dominant state and 0V-1V in the recessive state. When they are short-circuited, the differential voltage will drop significantly, remaining in the 0V-0.5V range, which is considered a short-circuit fault. The transceiver itself must meet two conditions simultaneously: first, the CAN-RX pin must have no signal output; second, the differential voltage of the CAN bus must be within the normal range of 2V-4V or 0V-1V, ensuring the fault is located in the transceiver itself rather than the bus line. The fault diagnosis algorithm also incorporates a time-based judgment condition during the judgment process; all voltage states must remain consistent for more than 50ms before a corresponding fault is identified, avoiding misjudgments due to instantaneous voltage fluctuations. The algorithm continuously reads the sampling data from the CAN bus status monitoring module and compares it one by one with preset judgment criteria, employing a logic of first judging the overall bus status and then subdividing the fault type to ensure the orderly and accurate fault identification.

[0045] Technical effects achieved: Clear quantitative standards for fault diagnosis, avoiding misdiagnosis and missed diagnosis, improving the reliability and accuracy of fault diagnosis algorithms, and providing clear basis for fault troubleshooting.

[0046] Technical problems with existing technologies: CAN bus differential voltage monitoring lacks clear sampling rules and anomaly judgment mechanisms, the sampling period is unreasonable or the anomaly judgment threshold is ambiguous, which makes it impossible to capture communication anomalies in a timely manner and affects the real-time performance of fault diagnosis.

[0047] Based on this, the differential voltage sampling period of the CAN bus status monitoring module is 1ms, and the normal range of differential voltage is 2V-4V in the dominant state and 0V-1V in the recessive state. The microcontroller unit is set with a monitoring time window of 10ms-50ms. When the differential voltage exceeds the normal range continuously within the set time window, a communication abnormality warning is triggered.

[0048] It's worth noting that the differential voltage sampling period of the CAN bus status monitoring module is set to 1ms. This setting is determined by comprehensively considering the CAN bus's maximum transmission rate of 1Mbps and the real-time requirements of fault diagnosis. The 1ms sampling period ensures that the monitoring module can quickly capture voltage changes when the bus signal changes, preventing data loss due to excessively long sampling intervals. The normal range of the differential voltage strictly follows the CAN 2.0 protocol specification. In the dominant state, 2V-4V is the normal differential voltage range for bus data transmission, and in the recessive state, 0V-1V is the normal voltage range when the bus is idle. This range has been verified through extensive experiments and is compatible with different brands and models of CAN bus transceivers. The monitoring time window set by the microcontroller unit can be adjusted according to the actual application scenario. The default setting is 30ms. When applied to scenarios with high requirements for communication latency, it can be adjusted to 10ms. When applied to scenarios with strong electromagnetic interference, it can be adjusted to 50ms to balance real-time performance and anti-interference capability. The logic for determining the monitoring time window is as follows: the microcontroller unit continuously counts the duration for which the differential voltage exceeds the normal range. When all continuously sampled differential voltages exceed the normal range, and the cumulative duration reaches the set monitoring time window duration, a communication anomaly warning is immediately triggered. The warning signal is output through the pin of the fault indication module, simultaneously notifying the fault diagnosis algorithm to initiate a detailed fault investigation process. During the monitoring process, the microcontroller unit also performs a moving average filter on the sampled data. After each sampling, the average value of the most recent 5 sampled data is calculated to reduce the fluctuation of sampled data caused by instantaneous electromagnetic interference and ensure the accuracy of anomaly determination. The filtered differential voltage data is not only used for anomaly warning but is also synchronously stored in the microcontroller unit's RAM for subsequent fault tracing and analysis.

[0049] Technical effects achieved: Clearly define the sampling period and anomaly judgment mechanism to ensure timely capture of CAN bus communication anomalies, improve the real-time performance and accuracy of fault early warning, and provide timely trigger signals for fault diagnosis.

[0050] The existing technology has the following technical problems: the signal transmission reliability of the fault indication module is insufficient and it lacks a fault tracing mechanism, making it impossible to record fault type information, which makes it difficult for maintenance personnel to quickly locate the root cause of the fault and affects maintenance efficiency.

[0051] Based on this, the fault indication module includes a fault flag pin and a CAN-INH pin; the fault flag pin is electrically connected to the ERR_N pin of the TJA1043T chip, and the CAN-INH pin is electrically connected to the CAN-INH-DET pin of the microcontroller unit through a resistor with a precision of 10KΩ±1%; after receiving a fault signal, the microcontroller unit records a 16-bit binary code fault code in its internal memory, with each fault type corresponding to a unique fault code.

[0052] It is worth mentioning that the fault flag pin is directly soldered to the ERR_N pin of the TJA1043T chip, forming a hardware-level fault signal transmission channel. When the chip detects abnormalities such as bus short circuits or over-temperature, the ERR_N pin will be immediately pulled low, and the fault flag pin will synchronously output a low level, quickly feeding back the fault status to the external system. This channel does not rely on software control and has a response time of less than 1μs. The CAN-INH pin is connected to the CAN-INH-DET pin of the microcontroller unit through a 10KΩ±1% precision metal film resistor. The 10KΩ resistor acts as a current limiting protection to prevent excessive pin current from damaging the chip. The microcontroller unit can enable or disable the CAN bus transceiver by controlling the level of the CAN-INH pin. When a serious fault is detected, the CAN-INH pin level will be pulled low to disable the transceiver and prevent the fault from escalating. The microcontroller unit's internal memory uses non-volatile flash memory, which can retain fault code data without loss after power failure. The fault codes are encoded using 16-bit binary codes, with different fault types corresponding to unique codes. The specific encoding rules are as follows: CAN-H open circuit corresponds to 0000000000000001, CAN-L open circuit corresponds to 0000000000000010, CAN-H short circuit to ground corresponds to 0000000000000100, CAN-L short circuit to power supply corresponds to 0000000000001000, CAN-H and CAN-L short circuit corresponds to 0000000000010000, and transceiver fault corresponds to 0000000000100000. When multiple faults occur simultaneously, the fault codes are encoded using a binary OR operation combination. After receiving a fault signal, the microcontroller unit immediately writes the corresponding fault code into the flash memory and records the time of the fault occurrence (based on the chip power-on time). The fault code storage adopts a cyclic overwrite mechanism, where the latest fault code overwrites the earliest stored fault code, and a maximum of 100 fault records can be stored. Maintenance personnel can read the fault codes in the flash memory through a dedicated diagnostic interface to quickly identify the fault type and the order of occurrence, providing a direct basis for fault diagnosis.

[0053] Technical effects achieved: Improved reliability of fault signal transmission, recording and tracing of fault types, helping maintenance personnel to quickly locate the root cause of faults and improve maintenance efficiency.

[0054] Technical problems with existing technologies: The microcontroller unit lacks a comprehensive self-test process after power-on, making it impossible to troubleshoot initial faults during the startup phase. This can easily lead to operation with faults, affecting the startup reliability of the interface circuit and the stability of subsequent operation.

[0055] Based on this, the self-test process of the microcontroller unit is as follows: First, after power-on, the static voltage of the CAN-H and CAN-L pins is detected for 200ms, and no CAN message is sent during the detection period; Second, the initial value of the CAN module error counter is read. If the initial value is greater than 0, an alarm is issued through the fault indication module; Third, a test message containing 8 bytes of data is sent, and after waiting for 100ms, a response message is detected. If no response is received, the communication link is determined to be faulty.

[0056] It's worth noting that the microcontroller unit's self-test process automatically starts after the chip's power-on reset, requiring no external trigger, ensuring troubleshooting is completed on every startup. The first step, static voltage detection, is set to 200ms to ensure the CAN bus stabilizes after power-on, avoiding detection errors caused by unstable bus voltage. No CAN messages are sent during the detection period to prevent signal transmission from affecting the static voltage detection results. During the detection process, the ADC module continuously collects voltage data from CAN-H and CAN-L, calculating the average voltage value over 200ms. If the average voltage value exceeds the normal static voltage range of 1.5V-3.5V, it is determined to be an initial power-on fault. The second step, reading the initial value of the error counter, is to check for initialization faults in the CAN module itself. The CAN module automatically resets the error counter after power-on; normally, the initial value should be 0. If the initial value is greater than 0, it indicates an abnormal CAN module initialization or a potential fault. In this case, a low-level alarm is output through the fault indicator module's fault flag pin to remind maintenance personnel to check the CAN module. The third step, test message sending and reply detection, is used to check the connectivity of the communication link. The test message contains 8 bytes of data, and the data content is fixed as hexadecimal 11, 22, 33, 44, 55, 66, 77, 88. This data combination is unique and easy to identify the reply message. After sending the test message, wait for 100ms. This time takes into account the transmission delay of the CAN bus and the processing time of the receiving end. If no reply message containing the same 8 bytes of data is received within 100ms, it is determined that the communication link is faulty. The fault may exist in the CAN bus transceiver, bus line, or receiving end device. The three steps of the self-test process are executed sequentially. The next step will only proceed after the previous step is passed. If any step fails, the self-test will stop immediately and a corresponding alarm will be issued through the fault indication module. At the same time, the fault code will be stored in the internal memory. The entire self-test process takes no more than 400ms and will not affect the normal startup sequence of the interface circuit.

[0057] The technical effects achieved are: to enable comprehensive fault diagnosis during the power-on phase, avoid operation with faults, improve the startup reliability and operational stability of the interface circuit, and reduce the risk of failure during subsequent operation.

[0058] Technical problems with existing technologies: The fault diagnosis methods of microcontroller units are limited, relying only on single data or single diagnostic functions, and lacking multi-dimensional auxiliary verification, resulting in insufficient reliability of fault identification and easy omissions.

[0059] Based on this, the auxiliary diagnostic methods of the microcontroller unit are as follows: send test messages at a 500ms cycle, wait 50ms for a reply after each transmission, and trigger the fault diagnosis process if no reply is received after 3 consecutive transmissions; sample the single-ended level of the CAN-H and CAN-L pins at a frequency of 10kHz through the ADC module, and process the sampled data through a moving average filter of 5 sampling points; receive diagnostic information such as explicit timeout, implicit bus monitoring, over-temperature, and under-voltage transmitted by the TJA1043T chip through the I2C communication interface.

[0060] It is worth mentioning that the microcontroller unit sends test messages at a 500ms cycle. This cycle setting balances communication resource usage with real-time diagnostics. The 500ms interval will not significantly affect normal communication, while enabling timely detection of communication link anomalies. After each test message is sent, a 50ms response is waited for. This 50ms wait time is sufficient to cover the maximum transmission delay of the CAN bus. The fault diagnosis process is only triggered after three consecutive failures to receive a response, avoiding false triggering due to single transmission interference. The ADC module samples the single-ended levels of CAN-H and CAN-L at a frequency of 10kHz. The 10kHz sampling frequency can capture subtle changes in the bus voltage. The sampled data is processed by a moving average filter of 5 sampling points. That is, after each sampling, the average of the current sampled value and the previous 4 sampled values ​​is taken as the valid data. This filtering method can effectively filter out sampling noise caused by high-frequency electromagnetic interference and improve data accuracy. The filtered single-ended level data is combined with the differential voltage data from the CAN bus status monitoring module to form a two-dimensional data verification, further ensuring the accuracy of fault diagnosis. The TJA1043T chip incorporates multiple diagnostic functions, including dominant timeout diagnostics, recessive bus monitoring, over-temperature diagnostics, and under-voltage diagnostics. This diagnostic information is transmitted to the microcontroller unit in real-time via the I2C communication interface at a rate of 100kbps, ensuring real-time accuracy. Dominant timeout diagnostics detects whether the bus has been in a dominant state for an extended period; recessive bus monitoring detects whether the bus has been inactive for a long time; over-temperature diagnostics monitors the chip junction temperature; and under-voltage diagnostics monitors the chip supply voltage. This diagnostic information supplements fault diagnosis from both the chip's own state and the bus's activity state, helping the microcontroller unit to more comprehensively determine the cause of the fault. The microcontroller unit cross-validates the data obtained from the three auxiliary diagnostic methods with the results of the main fault diagnosis algorithm. If multiple methods point to the same fault type, the fault determination result is confirmed; if contradictions exist, further investigation is initiated to ensure the reliability of fault identification.

[0061] Technical effects achieved: Multi-dimensional auxiliary diagnostic methods form cross-validation, improve the reliability and comprehensiveness of fault identification, reduce the risk of missed fault diagnosis, and provide richer data support for fault diagnosis.

[0062] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the technology of the present invention, and are not intended to limit the implementation methods of the technology of the present invention in any way. Any person skilled in the art can make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in the content of the present invention, but they should still be regarded as the technology or embodiments that are substantially the same as the present invention.

[0063] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this application, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A CAN bus transceiver interface circuit with intelligent fault diagnosis function, characterized in that, The system includes a CAN bus transceiver, a microcontroller unit, a CAN bus protection module, a CAN bus status monitoring module, and a fault indication module. The CAN-TX and CAN-RX pins of the CAN bus transceiver are electrically connected to the microcontroller unit, while the CAN-H and CAN-L pins are used to connect to the CAN bus. The CAN bus protection module is connected in series between the CAN bus transceiver and the CAN bus to suppress common-mode noise and absorb transient high voltage. The CAN bus status monitoring module is used to collect in real-time the differential voltage between the CAN-H and CAN-L pins, the absolute voltage level of the CAN-H pin relative to ground, and the absolute voltage level of the CAN-L pin relative to ground. The microcontroller unit has a built-in fault diagnosis algorithm that receives data from the CAN bus status monitoring module and identifies CAN-H open circuit, CAN-L open circuit, CAN-H short circuit to ground, CAN-L short circuit to power supply, CAN-H and CAN-L short circuit, and transceiver faults based on the collected data. The fault indication module is electrically connected to the microcontroller unit and receives fault signals output by the microcontroller unit to issue alarms. The CAN bus transceiver uses the TJA1043T chip. The CAN-H and CAN-L pins of the TJA1043T chip are electrically connected to the CAN bus protection module, and the CAN-TX and CAN-RX pins are electrically connected to the corresponding pins of the microcontroller unit. The TJA1043T chip has built-in bus short-circuit protection and over-temperature protection units, and also has an ERR_N pin as a fault signal output terminal. The microcontroller unit uses the S32K144 chip, which has built-in CAN module, ADC module, and error counter. The CAN1_RX pin of the CAN module is electrically connected to the CAN-RX pin of the CAN bus transceiver, and the CAN1_TX pin of the CAN module is electrically connected to the CAN-TX pin of the CAN bus transceiver. The ADC module is used to sample the absolute voltage levels of the CAN-H and CAN-L pins. The error counter is used to count the number of CAN signal transmission errors and reception errors. The threshold of the error counter is set to 128. The CAN bus status monitoring module includes a resistor divider network, a Zener diode, and a comparator. The resistor divider network consists of two 10KΩ±1% precision resistors. One end of one resistor is electrically connected to the CAN-H pin, and the other end is electrically connected to the non-inverting input of the comparator. One end of the other resistor is electrically connected to the CAN-L pin, and the other end is electrically connected to the inverting input of the comparator. The Zener diode is a BZT52C5V1TQ-7-F model, connected in parallel between the output of the resistor divider network and ground. The comparator is used to compare the output voltage of the resistor divider network with a preset threshold voltage and output a digital level signal to the microcontroller unit.

2. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The CAN bus protection module includes a common-mode inductor and a transient voltage suppressor. The common-mode inductor is model ACT45B-510-2P-TL003. Its two input terminals are electrically connected to the CAN-H and CAN-L pins of the CAN bus transceiver, respectively, and its two output terminals are electrically connected to the corresponding lines of the CAN bus. The transient voltage suppressor is model PESD2IVN24-T. Its two input terminals are electrically connected to the CAN-H and CAN-L pins of the CAN bus transceiver, respectively, and its output terminal is grounded.

3. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The fault diagnosis algorithm's fault judgment criteria are as follows: CAN-H open circuit corresponds to a CAN-L pin voltage in the range of 1.5V-3.5V and a CAN-H pin voltage that is consistently below 0.5V or above 4.5V; CAN-L open circuit corresponds to a CAN-H pin voltage in the range of 1.5V-3.5V and a CAN-L pin voltage that is consistently below 0.5V or above 4.5V; CAN-H short circuit to ground corresponds to a CAN-H pin voltage that is consistently below 0.5V; CAN-L short circuit to power supply corresponds to a CAN-L pin voltage that is consistently above 4.5V; CAN-H and CAN-L short circuit corresponds to a differential voltage between the two pins that is consistently in the range of 0V-0.5V; transceiver fault corresponds to a continuous absence of signal on the CAN-RX pin and a CAN bus differential voltage within the normal range.

4. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The differential voltage sampling period of the CAN bus status monitoring module is 1ms. The normal range of differential voltage is 2V-4V in the dominant state and 0V-1V in the recessive state. The microcontroller unit is set with a monitoring time window of 10ms-50ms. When the differential voltage exceeds the normal range continuously within the set time window, a communication abnormality warning is triggered.

5. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The fault indication module includes a fault flag pin and a CAN-INH pin. The fault flag pin is electrically connected to the ERR_N pin of the TJA1043T chip, and the CAN-INH pin is electrically connected to the CAN-INH-DET pin of the microcontroller unit through a resistor with a precision of 10KΩ±1%. After receiving a fault signal, the microcontroller unit records a 16-bit binary fault code in its internal memory. Different fault types correspond to unique fault codes.

6. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The self-test process of the microcontroller unit is as follows: First, after power-on, the static voltage of the CAN-H and CAN-L pins is detected for 200ms, and no CAN message is sent during the detection period; Second, the initial value of the CAN module error counter is read. If the initial value is greater than 0, an alarm is issued through the fault indication module; Third, a test message containing 8 bytes of data is sent, and the response message is detected after 100ms. If no response is received, it is determined that the communication link is faulty.

7. The CAN bus transceiver interface circuit with intelligent fault diagnosis function according to claim 1, characterized in that, The auxiliary diagnostic methods for the microcontroller unit are as follows: test messages are sent at 500ms intervals, and a 50ms response is waited after each transmission. If no response is received after 3 consecutive transmissions, the fault diagnosis process is triggered; the single-ended level of the CAN-H and CAN-L pins is sampled at a frequency of 10kHz through the ADC module, and the sampled data is processed by the moving average filtering of 5 sampling points; the dominant timeout, implicit bus monitoring, over-temperature and under-voltage diagnostic information transmitted by the TJA1043T chip through the I2C communication interface is received.

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