The CAN bus intelligent node design scheme is designed. It uses the LPC2294 with built-in multi-channel CAN bus controller as the main controller, and uses the isolated CAN transceiver CTM1050T as the transceiver, which makes the node small in size, low in power consumption and anti-interference. Good, so it is especially suitable for automotive, industrial control and medical systems and fault-tolerant maintenance buses.
1. Hardware design
1.1 Features of LPC2294
The LPC2294 is a powerful ultra-low power 32-bit microcontroller with ARM7TDMI core from PHILIPS. Internally embedded 256 KB of high-speed flash memory and 16 KB of static RAM. The 128-bit wide memory interface and unique acceleration structure allow 32-bit code to run at maximum clock rate (60MHz). Applications that have tight control over code size can use 16-bit Thumb mode to reduce code size by more than 30% with minimal performance loss.
Due to the LTC2294's 144-pin package, very low power consumption, two 32-bit timers, eight 10-bit ADCs, four interconnected CAN interfaces, PWM channels (six-way), and up to nine external interrupt pins They are especially suitable for automotive, industrial control applications as well as medical systems and fault-tolerant maintenance buses.
The LPC2294 integrates a 4-way CAN controller. They have the following characteristics:
â˜… Data transfer rate on a single bus is up to 1Mb/s
â˜… 32-bit register and RAM access
â˜… Compatible with CAN 2.0B, ISO 11898-1 standard
â˜… Global Acceptance Filter identifies 11-bit and 29-bit Rx identifiers for all CAN buses
â˜… Acceptance filter provides Full CAN-style automatic reception for selected standard identifiers
1.2 Isolated CAN Transceiver CTM1050T
The CTM1050T is an isolated high-speed CAN transceiver chip whose main function is to convert the logic level of the CAN controller to the differential level of the CAN bus, with (DC 2500V) isolation, ESD protection and TVS protection. Bus overvoltage function. The CTM1050T has the following features:
â˜† CAN transceiver fully compliant with CAN 2.0 and ISO 11898 standards
â˜† With isolation, ESD protection and TVS tube anti-bus overvoltage function;
â˜† The rate is up to 1Mbit/s;
â˜†Isolation voltage: DC 2500V
â˜† Electromagnetic radiation EME is extremely low, and electromagnetic immunity is extremely high;
â˜† It can be used directly without additional components.
1.3 CAN intelligent node hardware circuit design
The CAN intelligent node hardware circuit is shown in Figure 1.
Figure 1 is based on LPC2294 CAN bus intelligent node hardware circuit
The crystal frequency of the main controller LPC2294 ranges from 1 to 30 MHz. The crystal frequency of this design is 20MHz. Internal 256KB of high-speed flash memory for code and data storage. For FLASH memory, ISP In-System Programming or IAP In-ApplicaTIon Programming can be performed through the built-in serial JTAG interface. In order to facilitate debugging and system upgrades, these interface circuits can always be reserved in the design.
The LPC2294 is powered by dual power supplies. The CPU supply voltage range is 1.65 to 1.95V (1.8Â±0.15V), and the I/O supply voltage range is 3.0 to 3.6V (3.3Â±03V).
The isolated CAN bus transceiver CTM1050T is the interface between the CAN protocol controller and the physical bus. In the previous design, high-speed optocoupler (6N137), DC/DC power supply isolation module, CAN transceiver and other components are required to realize CAN transceiver circuit with isolation. Now, only one piece of CTM1050T interface chip can be used to isolate. CAN transceiver circuit, and the isolation voltage can reach DC 2500V.
1.4 hardware anti-jamming design
In the application of this design, there are many devices that generate electromagnetic signals, including ultrashort wave devices, audio devices, power supplies, etc., so anti-interference design is particularly important. The main measures were taken as follows:
(1) In order to further improve the anti-interference ability of the CAN bus node and ensure that the nodes are electrically isolated and independent, we use the isolated CAN transceiver CTM1050T to replace the traditional optocoupler and power isolation module to improve performance. Simultaneously simplify the circuit design.
(2) Two 120Î© resistors are added at both ends of the CAN bus. These two resistors play an important role in matching the bus impedance. Removing them will greatly reduce the anti-interference and reliability of data communication, and even fail to communicate.
(3) Two small 30pF capacitors are connected in parallel between CANH and CANL and ground, which can avoid high frequency interference on the bus and have certain anti-electromagnetic radiation capability.
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The following are the model parameters we product:
|APG-A||AL 16-70Â²||Single Bolt|
|APG-B1||AL 16-35Â²||Double Bolt|
|APG-B2||AL 16-70Â²||Double Bolt|
|APG-B3||AL 16-150Â²||Double Bolt|
|CAPG-A1||CU 6-50Â² AL 16-70/12Â²||Single Bolt|
|CAPG-A2||CU 10-95Â² AL 25-150Â²||Single Bolt|
|CAPG-B1||CU 6-50Â² AL 16-70Â²||Double Bolt|
|CAPG-B2||CU 10-95Â² AL 25-150Â²||Double Bolt|
|CAPG-C1||CU 16-120Â² AL 16-120Â²||Double Bolt|
|CAPG-C2||CU 50-240Â²AL 50-240Â²||Double Bolt|
|CAPG-D||CU 35-240Â²AL 35-300Â²||Tri-Bolt|
|Wire Core Section||16-120||50-240|
|Wire Core Section,mm2||10-95||16-120||50-240|
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