CN215268318U

CN215268318U - CAN bus resistance matching circuit

Info

Publication number: CN215268318U
Application number: CN202121359970.2U
Authority: CN
Inventors: 刘冰
Original assignee: Shanghai Tongli Information Technology Co ltd
Current assignee: Shanghai Tongli Information Technology Co ltd
Priority date: 2021-06-18
Filing date: 2021-06-18
Publication date: 2021-12-21
Anticipated expiration: 2031-06-18

Abstract

The utility model provides a CAN bus resistance matching circuit, include: the circuit comprises a MOS transistor Q1, a triode Q2, a first matching resistor R8, a second matching resistor R11 and a pull-up resistor R7; the base electrode of the triode Q2 forms an MCU control connection end, the emitting electrode of the triode Q2 is grounded, the collector electrode of the triode Q2 is respectively connected with the grid electrode of the MOS tube Q1 and the pull-up resistor R7, the drain electrode of the MOS tube Q1 is connected with one end of the first matching resistor R8, the other end of the first matching resistor R8 forms a first bus connection end, the source electrode of the MOS tube Q1 is connected with one end of the second matching resistor R11, and the other end of the second matching resistor R11 forms a second bus connection end. The utility model discloses guaranteeing under the correct condition of wiring, according to the exactness of CAN data, deciding whether to concatenate the bus with 120R resistance, simple and practical is lower to the installation requirement.

Description

CAN bus resistance matching circuit

Technical Field

The utility model relates to an electronic circuit specifically, relates to a CAN bus resistance matching circuit.

Background

According to the ISO 11898 specification, in order to enhance the reliability of CAN bus communication, a termination matching resistor (120 Ω) is usually added to two terminals of the CAN bus network, and the magnitude of the termination matching resistor is determined by the characteristic impedance of the transmission cable, for example, the characteristic impedance of a twisted pair is 120 Ω, and then the two terminals on the bus should also be matched with a 120 Ω termination resistor. The device plays a very important role in matching bus impedance, if the resistor is ignored, the anti-interference performance and reliability of digital communication are greatly reduced, even communication cannot be achieved, especially in a vehicle-mounted environment, a plurality of devices integrated on a CAN bus cannot determine which device is an endpoint device, sometimes the device needs to be connected with the CAN bus through a matching resistor with 120R, the device CAN normally communicate, sometimes the device needs to be connected with the CAN bus through a matching resistor without 120R, the device CAN normally communicate, and the 120R resistor is generally processed in the following modes:

1. whether 120R is connected in series with the CAN bus is achieved through the dial switch, structural problems need to be considered in circuit design, if the dial switch is arranged inside equipment, a machine needs to be disassembled every time, time and labor are wasted, if the dial switch is leaked on the structure, false triggering is possible, and more space needs to be sacrificed on the structure.

2. Whether 120R is connected in series with the CAN bus or not is realized by using a special change-over switch, and the general change-over switch in the mode CAN be damaged, needs a special chip and has higher cost.

3. Whether 120R is connected in series with the CAN bus or not is achieved by using 3 wires, when the space is limited too much, the method is not suitable, a special wiring mode needs to be marked during installation, if the connection is wrong, communication is not successful, and the installation needs to be disconnected again on site.

In chinese utility model patent document with publication number CN202159271U, a device for automatically matching CAN bus terminal resistance is disclosed, the device includes: the two ends of the resistor array are respectively connected with the two lines of the CAN bus; the control unit is used for sending test data, calculating the resistance value of a terminal resistor accessed to the CAN bus, and controlling whether the resistor in the resistor array is accessed to the CAN bus or not, and the control unit is connected with each switch in the resistor array; and the transceiver is used for receiving the test data from the control unit, receiving the test result from the bus, sending the test result to the control unit and sending the test data to the bus, and is respectively connected with the control unit and the CAN bus.

SUMMERY OF THE UTILITY MODEL

To the defect among the prior art, the utility model aims at providing a CAN bus resistance matching circuit.

According to the utility model provides a pair of CAN bus resistance matching circuit, include: the circuit comprises a MOS transistor Q1, a triode Q2, a first matching resistor R8, a second matching resistor R11 and a pull-up resistor R7; the base electrode of the triode Q2 forms an MCU control connection end, the emitting electrode of the triode Q2 is grounded, the collector electrode of the triode Q2 is respectively connected with the grid electrode of the MOS tube Q1 and the pull-up resistor R7, the drain electrode of the MOS tube Q1 is connected with one end of the first matching resistor R8, the other end of the first matching resistor R8 forms a first bus connection end, the source electrode of the MOS tube Q1 is connected with one end of the second matching resistor R11, and the other end of the second matching resistor R11 forms a second bus connection end.

Preferably, the MOS transistor Q1 is an NMOS transistor, and the triode Q2 is an NPN transistor.

Preferably, the pull-up resistor R7 is connected to a 5V power supply.

Preferably, the first matching resistor and the second matching resistor are both 60R4 in model.

Preferably, the base of the triode Q2 is connected in series with a current limiting resistor R9.

Preferably, a base of the triode Q2 is connected with a voltage dividing resistor R10, one end of the voltage dividing resistor R10 is connected with the base of the triode Q2, and the other end of the voltage dividing resistor R10 is grounded.

Preferably, a filter capacitor C7 is connected to a base of the transistor Q2, one end of the filter capacitor C7 is connected to the transistor Q2, and the other end of the filter capacitor C7 is grounded.

Preferably, a zener diode T1 is connected to the gate of the MOS transistor Q1, the anode of the zener diode T1 is connected to the gate of the MOS transistor Q1, and the cathode of the zener diode T1 is connected to the source of the MOS transistor Q1.

Preferably, the MOS transistor Q1 is model 2N 7002.

Preferably, the model of the triode Q2 is MMBT 3904.

Compared with the prior art, the utility model discloses following beneficial effect has:

1. the circuit provided by the invention has the advantages of fewer required components, low cost, small volume and small occupied area of the PCB.

2. Under the condition of ensuring correct wiring, whether the 120R resistor is connected into the bus in series or not is determined according to the correctness of CAN data, and the method is simple and practical and has lower installation requirements.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

fig. 1 is a circuit diagram of a CAN bus resistor matching circuit of the present invention.

Detailed Description

The present invention will be described in detail with reference to the following embodiments. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that various changes and modifications can be made by one skilled in the art without departing from the spirit of the invention. These all belong to the protection scope of the present invention.

As shown in fig. 1, the utility model provides a CAN bus resistance matching circuit, include: the circuit comprises a MOS transistor Q1, a triode Q2, a first matching resistor R8, a second matching resistor R11, a pull-up resistor R7, a current-limiting resistor R9, a voltage-dividing resistor R10, a filter capacitor C7 and a Zener diode T1. The MOS transistor Q1 is 2N7002, the triode Q2 is MMBT3904, and the first matching resistor R8 and the second matching resistor R11 are both 60R 4.

The base of the triode Q2 forms an MCU control connection end and is connected with the MCU _ ODT _ SWITCH, the base of the triode Q2 is also connected with one end of a divider resistor R10 and one end of a filter capacitor C7, and the other end of the divider resistor R10 and the other end of the filter capacitor C7 are both connected with the emitter of the triode Q2 and grounded. A current limiting resistor R9 is connected in series with the base of the triode Q2, one end of the current limiting resistor R9 is connected with the MCU _ ODT _ SWITCH, and the other end of the current limiting resistor R9 is connected with one end of the voltage dividing resistor R10 and one end of the filter capacitor C7 respectively.

The collector of the transistor Q2 is connected to the gate of the MOS transistor Q1, one end of a pull-up resistor R7, and the anode of the zener diode T1, respectively, wherein the other end of the pull-up resistor R7 is connected to a 5V power supply. The drain electrode of the MOS transistor Q1 is connected to one end of the first matching resistor R8, the other end of the first matching resistor R8 forms a first bus connection end, the source electrode of the MOS transistor Q1 is connected to one end of the second matching resistor R11, and the other end of the second matching resistor R11 forms a second bus connection end. The cathode of the zener diode T1 is connected to one end of the second matching resistor R11.

The automatic matching circuit of the CAN bus matching resistor is automatically switched into the following two conditions:

1. when the MCU _ ODT _ SWITCH outputs a high level of 3.3V, the current-limiting resistor R9 and the voltage-dividing resistor R10 divide the 3.3V level into 1.65V, the filter capacitor C7 prevents external interference, which causes the mis-triggering of the transistor Q2, at this time, the Vbe voltage of the transistor Q2 is >0.7V, the transistor Q2 is turned on, the Vg voltage of the MOS transistor Q1 is 0V (close to 0V), since the source of the MOS transistor is connected to CANL on the CAN bus through the second matching resistor R11, the dominant level of CANL is 1.5V and the recessive level is 2.5V according to the CAN communication standard, so the Vgs voltage is always smaller than the turn-on voltage of the MOS transistor Q1, the MOS transistor Q1 is always off, and at this time, the first matching resistor R8 and the second matching resistor R11, the two 60.4R resistors are not connected between CANH and CANL.

2. When the MCU _ ODT _ SWITCH outputs a low level (less than 0.7V), the low level is divided through the current limiting resistor R9 and the voltage dividing resistor R10 until the base voltage of the transistor Q2 is less than 0.7V, the filter capacitor C7 prevents external interference, the transistor Q2 is caused to trigger by mistake, the Vbe voltage of the transistor Q2 is less than 0.7V at the moment, the transistor Q2 is not conducted, the Vg voltage of the MOS transistor Q1 is pulled up to 5V through the pull-up resistor R7, as the source level of the MOS transistor is connected to CANL on the CAN bus through the second matching resistor R11, the dominant level of the CANL is 1.5V according to the CAN communication standard, the recessive level is 2.5V, the voltage of Vgs is always greater than the turn-on voltage of the MOS transistor Q1 by 2.1V, the MOS transistor Q1 is always conducted, and at the moment, the two resistors 60.4R of the first matching resistor R8 and the second matching resistor R11 are connected between CANH and CANL.

Note that the low level here means equal to or close to 0V; high means at or near the supply voltage.

In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.

The foregoing description of the specific embodiments of the invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims

1. A CAN bus resistance matching circuit, comprising: the circuit comprises a MOS transistor Q1, a triode Q2, a first matching resistor R8, a second matching resistor R11 and a pull-up resistor R7; the base electrode of the triode Q2 forms an MCU control connection end, the emitting electrode of the triode Q2 is grounded, the collector electrode of the triode Q2 is respectively connected with the grid electrode of an MOS tube Q1 and a pull-up resistor R7, the drain electrode of the MOS tube Q1 is connected with one end of a first matching resistor R8, the other end of the first matching resistor R8 forms a first bus connection end, the source electrode of the MOS tube Q1 is connected with one end of a second matching resistor R11, and the other end of the second matching resistor R11 forms a second bus connection end.

2. The CAN bus resistor matching circuit of claim 1, wherein: the MOS transistor Q1 is an NMOS transistor, and the triode Q2 is an NPN transistor.

3. The CAN bus resistor matching circuit of claim 1, wherein: the pull-up resistor R7 is connected with a 5V power supply.

4. The CAN bus resistor matching circuit of claim 1, wherein: the first matching resistor and the second matching resistor are both 60R4 in model.

5. The CAN bus resistor matching circuit of claim 1, wherein: the base of the triode Q2 is connected in series with a current limiting resistor R9.

6. The CAN bus resistor matching circuit of claim 1, wherein: the base electrode of the triode Q2 is connected with a voltage division resistor R10, one end of the voltage division resistor R10 is connected with the base electrode of the triode Q2, and the other end of the voltage division resistor R10 is grounded.

7. The CAN bus resistor matching circuit of claim 1, wherein: the base electrode of the triode Q2 is connected with a filter capacitor C7, one end of the filter capacitor C7 is connected with the triode Q2, and the other end of the filter capacitor C7 is grounded.

8. The CAN bus resistor matching circuit of claim 1, wherein: the gate of the MOS transistor Q1 is connected with a zener diode T1, the anode of the zener diode T1 is connected with the gate of the MOS transistor Q1, and the cathode of the zener diode T1 is connected with the source of the MOS transistor Q1.

9. The CAN bus resistor matching circuit of claim 1, wherein: the MOS transistor Q1 is model 2N 7002.

10. The CAN bus resistor matching circuit of claim 1, wherein: the model of the triode Q2 is MMBT 3904.