TJA1055T-1 CAN transceiver Fault: Identifying Incorrect Resistor Settings

Fault Analysis: TJA1055T/1 CAN Transceiver Fault - Identifying Incorrect Resistor Settings

Fault Cause:

The TJA1055T/1 CAN transceiver is designed to facilitate Communication in a CAN (Controller Area Network) system. When facing a fault related to this transceiver, one of the common causes is incorrect resistor settings. These settings affect the proper functioning of the transceiver, leading to issues like communication failure or improper signal transmission. Incorrect resistor settings can cause problems such as:

Bus Termination Issues: The CAN bus requires proper termination Resistors (typically 120 ohms) at both ends of the bus. If the resistors are missing, incorrectly placed, or have incorrect values, the transceiver might not be able to properly transmit or receive signals.

Biasing Resistor Problems: Biasing resistors help maintain the correct voltage levels on the CAN bus. If these resistors are incorrectly sized or positioned, it can cause incorrect signaling or make the transceiver unable to detect signals correctly.

Faulty CAN Bus Design: An improper resistor setup may cause reflections or signal integrity issues, disrupting communication. This might result in the transceiver being unable to communicate with other devices on the network.

Possible Faults from Incorrect Resistor Settings: No Communication: The CAN transceiver cannot send or receive any messages due to improper bus termination or biasing. Error Frames: The transceiver might constantly detect errors, resulting in frequent error frames. Signal Distortion: Incorrect resistor values can lead to signal integrity issues, resulting in corrupted data. Low-Speed Communication: If the transceiver is incorrectly terminated, the communication speed may drop unexpectedly. Solution to Resolve the Fault:

To resolve this issue, follow these steps to ensure the correct resistor settings for the TJA1055T/1 CAN transceiver:

Step 1: Check Bus Termination Resistors Requirement: The CAN bus must be properly terminated with a 120-ohm resistor at both ends. Action: Check if both ends of the CAN bus are properly terminated with 120-ohm resistors. Ensure that there are no additional resistors in the middle of the bus unless specified by the design. If necessary, replace missing or incorrect resistors with the appropriate 120-ohm value. Step 2: Verify Biasing Resistor Values Requirement: The transceiver requires proper biasing for the CANH and CANL lines to work correctly. Action: Verify the value of any biasing resistors. Typically, these should be between 1kΩ and 10kΩ, depending on the transceiver specifications. Ensure the resistors are placed correctly between the CANH and CANL lines as well as the ground or VCC lines. Step 3: Examine PCB Layout and Connections Requirement: Ensure there are no issues in the PCB layout that could affect the resistor connections. Action: Inspect the PCB for any physical damage or incorrect routing of the CAN signals. Ensure that the resistor networks are connected properly according to the datasheet or design specifications. Step 4: Test the CAN Bus Requirement: After addressing the resistor settings, verify the functionality of the CAN bus. Action: Use a CAN analyzer or a compatible diagnostic tool to check if the transceiver is correctly transmitting and receiving data. Monitor the bus for any error frames, and ensure normal communication is restored. Step 5: Check for External Interference Requirement: Ensure that external noise or interference is not affecting the CAN bus signals. Action: Ensure that the CAN bus wires are properly shielded and that they are not running parallel to high-voltage or high-frequency lines that could introduce noise. Keep the bus short and ensure there are no loops in the wiring. Step 6: Revalidate the System Requirement: Confirm that the CAN system operates correctly after adjustments. Action: After resolving the resistor issues, run a full system test to verify that all connected nodes can communicate without issues. Check the error counters and ensure that no more errors are detected by the transceiver.

By carefully addressing the incorrect resistor settings, you can restore proper communication on the CAN bus and ensure the TJA1055T/1 transceiver operates as expected.