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Addressing Incorrect Bus Termination in TJA1055T-1 CAN transceiver Circuits

Addressing Incorrect Bus Termination in TJA1055T/1 CAN Transceiver Circuits

1. Understanding the Problem

The TJA1055T/1 CAN transceiver is a widely used device for Communication in automotive and industrial CAN networks. One of the common issues that engineers face while designing circuits with this transceiver is incorrect bus termination. This issue can lead to communication failures or unreliable CAN data transfer, and understanding its root causes is essential to resolving it effectively.

Incorrect bus termination occurs when the CAN bus is not properly terminated with the correct resistances at both ends of the bus, or when there are other errors in the circuit. It can cause signal reflections, loss of data integrity, or unreliable communication between devices.

2. Causes of Incorrect Bus Termination

Here are the main causes that can lead to incorrect bus termination in TJA1055T/1 CAN transceiver circuits:

Missing Termination Resistors : The most common cause is failing to place termination resistors at the two ends of the CAN bus. According to the CAN protocol, the bus should have a 120Ω resistor at each end to prevent signal reflections and ensure proper communication.

Incorrect Resistor Values: If the termination resistors are not the correct 120Ω value (or are too high or low), it can distort the signal and cause communication issues.

Multiple Resistors at One End: Sometimes, engineers may mistakenly place termination resistors at both ends of the bus or multiple resistors at a single point, leading to short circuits or improper termination.

Damaged Resistor or Connections: A physically damaged resistor or poor soldering/connection at the termination points can create an open circuit or intermittent connections, preventing proper communication.

Incorrect Pin Configuration on Transceivers : Sometimes, the issue might not be with the resistors themselves but with how the TJA1055T/1 transceiver is configured, especially if it has an internal termination option. Misconfiguration can bypass the external termination resistors, leading to issues.

3. How to Detect Incorrect Bus Termination

If you're experiencing issues with communication in your CAN network, here's how you can troubleshoot and identify termination problems:

Check for Bus Communication Failure: The most common sign of incorrect termination is a failure in CAN communication. The devices may not communicate, or error frames may be detected.

Use an Oscilloscope: Using an oscilloscope, you can check the signal quality on the CAN bus. If the termination is incorrect, you may notice reflections or distorted signals.

Look for Physical Damage: Visually inspect the termination resistors and ensure that they are physically intact and correctly placed at both ends of the bus.

4. Step-by-Step Solution to Fix Incorrect Bus Termination

Here’s a practical guide on how to solve the incorrect bus termination issue:

Step 1: Confirm the Placement of Termination Resistors

Ensure that there is a 120Ω resistor placed at each end of the CAN bus, as required by the CAN standard. Double-check that there is no additional resistor or incorrect placement at other points on the bus.

Step 2: Verify the Resistor Value

Use a multimeter to confirm that the value of the termination resistor is indeed 120Ω. Any resistor with a different value (e.g., 100Ω, 150Ω) can cause signal problems.

Step 3: Inspect Transceiver Pin Configuration

If you are using the TJA1055T/1, ensure that its termination settings are correct. Some transceivers, like the TJA1055, have internal termination, which may conflict with external resistors if not properly configured. Refer to the datasheet to ensure that the TXD and RXD pins are connected correctly and that no additional internal resistors are enabled when external resistors are in place.

Step 4: Test with Known Working Setup

If you still experience issues, replace the resistors with new ones or swap in known working transceivers. This helps rule out faulty components.

Step 5: Check for Faulty Connections

Inspect the soldering and wiring for any loose connections or shorts. A poor connection at the termination point can cause intermittent communication problems.

Step 6: Use Proper Cable Length and Quality

Ensure the CAN bus cables are of the correct length. A bus that’s too long or has poor-quality wiring can cause issues even if termination resistors are placed correctly. 5. Preventing Future Termination Issues Standardize Resistor Placement: Always adhere to the CAN bus standard by placing termination resistors at both ends and ensuring they are correctly valued. Use Termination Detection Tools: Tools like the CAN bus analyzer or an oscilloscope can help detect issues early in the design phase. Review Transceiver Settings: When using advanced transceivers like the TJA1055T/1, always check the configuration options to ensure no internal termination conflicts. Documentation: Always refer to datasheets and application notes for guidance on the correct setup of CAN transceivers in your circuits. 6. Conclusion

Incorrect bus termination in TJA1055T/1 CAN transceiver circuits is a common issue that can disrupt communication in CAN networks. By following a systematic approach—ensuring proper resistor placement, verifying resistor values, inspecting connections, and checking the configuration of the transceiver—you can quickly identify and solve termination problems. Proper termination ensures reliable communication and stable CAN network performance.