Controller area network (CAN) bus terminal resistor control switch circuit

Abstract

The utility model relates to the technical field of CAN bus control, in particular to a CAN bus terminal resistance control switch circuit, which comprises a CAN transceiver, an NMOS (N-channel Metal Oxide Semiconductor) switch module and a micro-control chip, and is characterized in that the CAN transceiver comprises a first pin, a second pin, a sixth pin and a seventh pin, and the first pin and the fourth pin are respectively connected with a CAN bus; the seventh pin is connected with one end of the terminal resistor, and the other end of the terminal resistor is connected with the MOSFET switch module; the MOSFET switch module comprises a first NMOS tube and a second NMOS tube which are connected with each other, the D pole of the first NMOS tube is connected with the terminal resistor, the S pole of the first NMOS tube is connected with the sixth pin, the G pole of the first NMOS tube is connected with the D pole of the second NMOS tube, and the G pole of the second NMOS tube is connected with the micro-control chip. The circuit is simple in structure, few in device, low in cost, small in occupied space of a circuit board and convenient to control, control can be achieved only by sending out a high-low level through a micro-control chip, and manual maintenance and assembly are not needed.

Description

Technical Field

[0001] This utility model relates to the field of CAN bus control technology, and in particular to a CAN bus terminating resistor control switch circuit. Background Technology

[0002] Controller Area Network (CAN) is a serial communication protocol bus used in real-time applications. It uses twisted-pair cabling to transmit signals and is one of the most important and widely used fieldbuses. The CAN protocol is used for communication between multiple electronic devices, replacing outdated wiring schemes to save costs and provide reliability. Its robustness extends its application to other automation and industrial applications. The CAN bus termination resistor is typically 120Ω, and its function is mainly reflected in the following three aspects:

[0003] 1. Improve anti-interference capability: By helping high-frequency, low-energy signals to attenuate rapidly, reducing the load and electromagnetic interference on the line, and suppressing sudden noise interference, the system can ensure stable operation and enhance the reliability of the vehicle control system.

[0004] 2. Ensure the bus quickly enters a recessive state: The energy decays more rapidly through parasitic capacitance, helping the bus quickly enter a low-energy state and reducing unnecessary signal interference.

[0005] 3. Improve signal quality: By placing it at both ends of the bus, reflection energy is reduced, thereby improving signal quality and transmission efficiency.

[0006] Termination resistors are typically connected between two CAN lines, and their on / off state is controlled by a switch connected in series with the resistor. Current methods for controlling the on / off state of the resistor are as follows:

[0007] Relay control: A relay is connected in series between two CAN lines, and controlling the relay's conduction controls the connection of the terminating resistor. However, relay control circuits are bulky and expensive.

[0008] Fuse control: A fuse is connected in series between the two CAN lines. By applying a large current to the fuse and blowing it, the connection of the terminating resistor is controlled. However, fuse control can only achieve single-use control; a new fuse is required each time the configuration is changed.

[0009] Manual shorting switch: This type of switch is connected in series between two CAN lines via a pin header shorting cap or a switch connector, and is manually controlled by a mechanical switch. While simple and reliable, manual shorting switches require manual configuration, and for waterproof or dustproof equipment, disassembly is necessary, which can affect equipment performance.

[0010] Therefore, a new technical solution is urgently needed to solve the above-mentioned technical problems. Utility Model Content

[0011] The purpose of this invention is to overcome the problems of the prior art and provide a CAN bus terminating resistor control switch circuit to solve the technical problems of existing technologies that use mechanical contacts, such as relay control, fuse control, and manual short-circuit switches, which have large electrical control volume and high cost, fuses can only achieve single-use control, and manual short-circuit switches require manual disassembly and configuration.

[0012] The above objectives are achieved through the following technical solutions:

[0013] A CAN bus terminating resistor control switch circuit includes a CAN transceiver, an NMOS switching module, and a microcontroller chip. The CAN transceiver includes a first pin, a second pin, a sixth pin, and a seventh pin. The first pin and the fourth pin are respectively connected to the CAN bus. The seventh pin is connected to one end of a terminating resistor, and the other end of the terminating resistor is connected to the MOSFET switching module. The MOSFET switching module includes a first NMOS transistor and a second NMOS transistor connected to each other. The drain (D) of the first NMOS transistor is connected to the terminating resistor, the source (S) of the first NMOS transistor is connected to the sixth pin, the gate (G) of the first NMOS transistor is connected to the drain (D) of the second NMOS transistor, and the gate (G) of the second NMOS transistor is connected to the microcontroller chip.

[0014] Furthermore, the resistance of the terminating resistor is 120Ω.

[0015] Furthermore, the gate of the first NMOS transistor is pulled up to a 10V power supply through a first resistor and a second resistor.

[0016] Furthermore, a first capacitor, a third resistor, and a fourth resistor are provided between the gate and source of the second NMOS transistor to form a gate drive circuit.

[0017] Furthermore, both the first NMOS transistor and the second NMOS transistor are BSS138.

[0018] Furthermore, a first self-resetting fuse is provided between the seventh pin (CANH) and the terminating resistor, and a second self-resetting fuse is provided between the sixth pin and the source terminal of the first NMOS transistor.

[0019] Furthermore, the CAN transceiver also includes an eighth pin, between which a fifth resistor and a first transient voltage suppression diode are provided, and a second transient voltage suppression diode is provided on the sixth pin and grounded.

[0020] Furthermore, the CAN transceiver also includes a third pin, which is connected to a 5V power supply and decoupled from the power supply through a second capacitor.

[0021] Furthermore, the CAN transceiver also includes a fifth pin, which is connected to a 3V power supply and decoupled from the power supply through a third capacitor.

[0022] Furthermore, the model of the CAN transceiver is TCAN1051HDR.

[0023] The CAN bus terminating resistor control switch circuit provided by this utility model is not only simple in structure, with few components, low cost, and little space occupied on the circuit board, but also easy to control. It can be controlled by only a high or low level output from the microcontroller chip, without the need for manual maintenance and assembly. Attached Figure Description

[0024] Figure 1 This is a circuit diagram of a CAN bus terminating resistor control switch circuit according to the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] like Figure 1 As shown, this solution provides a CAN bus terminating resistor control switch circuit, including a CAN transceiver U28, an NMOS switching module, and a microcontroller chip (not labeled in the figure). The CAN transceiver U28 includes a first pin TXD, a second pin GND, a sixth pin CANL, and a seventh pin CANH. The first pin TXD and the fourth pin RXD are respectively connected to the CAN bus; the seventh pin CANH is connected to one end of the terminating resistor R178, and the other end of the terminating resistor R178 is connected to the MOSFET switching module.

[0027] The MOSFET switching module includes a first NMOS transistor Q23 and a second NMOS transistor Q24 connected to each other. The drain (D) of the first NMOS transistor Q23 is connected to the terminating resistor R178, the source (S) of the first NMOS transistor Q23 is connected to the sixth pin CANL, the gate (G) of the first NMOS transistor Q23 is connected to the drain (D) of the second NMOS transistor Q24, and the gate (G) of the second NMOS transistor Q24 is connected to the microcontroller chip.

[0028] The terminating resistor R178 has a resistance of 120Ω.

[0029] In this embodiment, the gate of the first NMOS transistor Q23 is pulled up to a 10V power supply through the first resistor R181 and the second resistor R182.

[0030] The CAN transceiver U28 mentioned above is model TCAN1051HDR, a CAN (Controller Area Network) transceiver manufactured by Texas Instruments.

[0031] Working principle:

[0032] When the CAN bus is affected by electromagnetic interference, overvoltage, and overcurrent, the microcontroller chip sends a high-level signal of 3.3V to the base of the second NMOS transistor Q24 to control it, thereby pulling down the base of the first NMOS transistor Q23 and realizing the disconnection control of the terminating resistor R178.

[0033] When the electromagnetic interference, overvoltage, and overcurrent effects on the CAN bus disappear, the microcontroller chip sends a low-level signal to the base of the second NMOS transistor Q24 for control. When the base of the second NMOS transistor Q24 is 0V, the base of the first NMOS transistor Q23 is pulled up to 10V, thereby realizing the conduction control of the terminating resistor R178.

[0034] like Figure 1 As shown, as an optimization of this embodiment, a first capacitor C78, ​​a third resistor R183, and a fourth resistor R185 are provided between the gate and source of the second NMOS transistor Q24 to form a gate drive circuit.

[0035] Specifically, the third resistor R183 is used to limit the gate current and protect the MOSFET gate from damage caused by excessive current. When the second NMOS transistor Q24 needs to be turned off, the third resistor R183 provides a discharge path, allowing the gate voltage to drop quickly to the 0V ground potential.

[0036] The fourth resistor R185 provides a pull-up resistor to ensure that the gate voltage is pulled high to the power supply voltage when no other signal drives the gate, thereby keeping the second NMOS transistor Q24 in the off state.

[0037] The first capacitor C78 serves as a bypass capacitor, connected between the fourth resistor R185 and ground. Together with the fourth resistor R185, it forms an RC filter to filter out high-frequency noise in the gate drive signal, stabilize the gate voltage, and prevent malfunction of the second NMOS transistor Q24. Furthermore, it can accelerate the switching speed of the second NMOS transistor Q24 because it can provide instantaneous gate current, helping the MOSFET to turn on and off more quickly.

[0038] The first NMOS transistor Q23 and the second NMOS transistor Q24 are both BSS138.

[0039] like Figure 1 As shown, a first self-resetting fuse R175 is provided between the seventh pin CANH and the terminating resistor R178, and a second self-resetting fuse R176 is provided between the sixth pin CANL and the source terminal of the first NMOS transistor Q23.

[0040] This embodiment uses a first self-resetting fuse R175 and a second self-resetting fuse R176 to provide overcurrent protection for the CANH and CANL pins.

[0041] The CAN transceiver U28 also includes an eighth pin S. A fifth resistor R172 and a first transient voltage suppression diode TVS28 are provided between the eighth pin S and the seventh pin CANH. A second transient voltage suppression diode TVS29 is also provided on the sixth pin CANL and grounded.

[0042] Specifically, in this embodiment, a first transient voltage suppressor diode TVS28 and a second transient voltage suppressor diode TVS29 are used to provide overvoltage protection for the sixth pin CANL and the seventh pin CANH of the CAN transceiver U28 to prevent electrostatic discharge and voltage spikes.

[0043] In this embodiment, the first transient voltage suppression diode TVS28 and the second transient voltage suppression diode TVS29 are model SMBJ6.0AH\6.0\.

[0044] The CAN transceiver U28 also includes a third pin VCC, which is connected to a 5V power supply and decoupled from the power supply through a second capacitor C75.

[0045] The CAN transceiver U28 also includes a fifth pin, VIO, which is connected to a 3V power supply and decoupled from the power supply through a third capacitor, C77.

[0046] The above description is only for illustrating the embodiments of this utility model and is not intended to limit this utility model. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A CAN bus termination resistor control switch circuit, characterized by, The CAN transceiver (U28) includes a first pin (TXD), a second pin (GND), a sixth pin (CANL) and a seventh pin (CANH), wherein the first pin (TXD) and the fourth pin (RXD) are connected with the CAN bus respectively; one end of the seventh pin (CANH) is connected with the terminal resistor (R178), and the other end of the terminal resistor (R178) is connected with the MOSFET switch module. The MOSFET switch module includes a first NMOS tube (Q23) and a second NMOS tube (Q24) connected with each other, wherein the D pole of the first NMOS tube (Q23) is connected with the terminal resistor (R178), the S pole of the first NMOS tube (Q23) is connected with the sixth pin (CANL), the G pole of the first NMOS tube (Q23) is connected with the D pole of the second NMOS tube (Q24), and the G pole of the second NMOS tube (Q24) is connected with the micro control chip.

2. A CAN bus termination resistor control switch circuit according to claim 1, characterized in that The resistance value of the terminal resistor (R178) is 120Ω.

3. A CAN bus termination resistor control switch circuit according to claim 2, characterised in that, The G pole of the first NMOS tube (Q23) is pulled up to the 10V power supply through the first resistor (R181) and the second resistor (R182).

4. A CAN bus termination resistor control switch circuit according to claim 1 or 2, characterized in that, The G pole and the S pole of the second NMOS tube (Q24) are provided with the first capacitor (C78), the third resistor (R183) and the fourth resistor (R185), thereby forming a gate drive circuit.

5. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that, The models of the first NMOS tube (Q23) and the second NMOS tube (Q24) are both BSS138.

6. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that The first self-resetting fuse (R175) is arranged between the seventh pin (CANH) and the terminal resistor (R178), and the second self-resetting fuse (R176) is arranged between the sixth pin (CANL) and the S pole of the first NMOS tube (Q23).

7. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that, The CAN transceiver (U28) further includes an eighth pin (S), wherein the fifth resistor (R172) and the first transient voltage suppression diode (TVS28) are arranged between the eighth pin (S) and the seventh pin (CANH), and the second transient voltage suppression diode (TVS29) is arranged on the sixth pin (CANL) and grounded.

8. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that, The CAN transceiver (U28) further includes a third pin (VCC), wherein the third pin (VCC) is connected with the 5V power supply and is decoupled by the second capacitor (C75).

9. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that, The CAN transceiver (U28) further includes a fifth pin (VIO), wherein the fifth pin (VIO) is connected with the 3V power supply and is decoupled by the third capacitor (C77).

10. The CAN bus termination resistor control switch circuit according to claim 1, characterized in that The model of the CAN transceiver (U28) is TCAN1051HDR.

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