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Low Signal Integrity in TJA1043T-1J CAN Transceivers A Common Issue

Low Signal Integrity in TJA1043T-1J CAN transceiver s A Common Issue

Low Signal Integrity in TJA1043T/1J CAN Transceivers : A Common Issue and How to Solve It

Introduction: Low signal integrity in CAN (Controller Area Network) transceivers, like the TJA1043T/1J, can cause Communication failures or errors in automotive and industrial applications. Signal integrity issues typically manifest as data corruption, frequent retransmissions, or communication interruptions. Understanding the root causes of these problems and how to address them is essential for ensuring smooth, reliable CAN communication. Below, we will discuss common causes of low signal integrity in TJA1043T/1J transceivers and provide a step-by-step guide on how to resolve them.

Causes of Low Signal Integrity:

Improper PCB Layout: A common cause of poor signal integrity is an improper PCB (Printed Circuit Board) layout. Issues like long trace lengths, inadequate grounding, and improper routing of the CANH and CANL signals can cause reflections, noise, and signal attenuation.

Termination Resistor Problems: CAN bus systems require termination Resistors to prevent signal reflections. If the termination resistors are missing, improperly valued, or not placed at the correct locations, signal degradation can occur, leading to low signal integrity.

Electromagnetic Interference ( EMI ): External noise or EMI from nearby electronic devices can corrupt CAN signals, especially in environments with heavy electrical equipment. Without proper shielding or filtering, this interference can drastically reduce signal quality.

Improper Voltage Levels: The TJA1043T/1J transceiver operates within specific voltage ranges. If the supply voltage or the voltage levels on the CAN bus are too low or unstable, signal integrity can degrade.

Incorrect Cable Type or Length: The physical wiring of the CAN bus is also critical. Using cables with improper impedance or excessively long cables can introduce signal attenuation and reflections, which compromises signal integrity.

Step-by-Step Guide to Resolve Low Signal Integrity:

Step 1: Review PCB Layout Action: Ensure that the traces for CANH and CANL are as short and as matched in length as possible. Use a ground plane to minimize noise and reduce the risk of electromagnetic interference. Why: Proper PCB layout ensures that the signals travel with minimal resistance and noise, improving their integrity. Tip: Implement a differential pair for CANH and CANL signals, ensuring that both traces are routed parallel to each other and at the correct impedance (typically 120Ω). Step 2: Check Termination Resistors Action: Verify that 120Ω resistors are placed at both ends of the CAN bus. These resistors are crucial for maintaining the integrity of the signals and preventing reflections. Why: Termination resistors match the impedance of the bus and ensure that the signal is properly absorbed at both ends of the network. Tip: Check that the resistors are correctly rated (120Ω) and securely connected. If you're unsure, replace them with known good components. Step 3: Minimize Electromagnetic Interference (EMI) Action: Use proper shielding on the CAN bus cables to protect against EMI. Additionally, use capacitor s and filters to reduce high-frequency noise. Why: EMI from surrounding devices can corrupt CAN signals, leading to data corruption or loss. Shielding and filtering help mitigate this risk. Tip: For high-EMI environments, consider using twisted pair cables for CANH and CANL to further reduce noise pickup. Step 4: Verify Voltage Levels Action: Check the supply voltage to the TJA1043T/1J transceiver and ensure it meets the specifications. For example, the Vcc should typically be between 4.5V and 5.5V. Why: Low or unstable voltages can cause malfunction in the transceiver, affecting signal integrity. Tip: Use a stable power supply and ensure that there is no significant voltage drop across the power lines. Step 5: Check CAN Bus Wiring Action: Ensure that the CAN bus wiring is of the correct type and length. Use twisted-pair cables with the correct impedance (typically 120Ω) for the best signal quality. Avoid excessively long cable runs. Why: Using the wrong cable type or running the cable too long can cause signal loss or reflections, leading to data errors. Tip: Keep the cable lengths as short as possible and avoid running cables near high-power sources that can induce noise.

Testing and Validation:

Once the steps above have been implemented, the next step is testing the CAN network to ensure that the signal integrity has been improved:

Use an Oscilloscope: Measure the signal on the CANH and CANL lines using an oscilloscope. You should see a clean differential signal without significant noise or distortion. Expected result: A differential signal with a voltage swing of approximately 3.5V to 4.5V, with clean transitions between logic high and low. Check Communication Stability: Test the CAN bus by sending messages between devices and monitor for errors or communication interruptions. Expected result: No bus errors (such as CRC or form errors) and stable communication without retransmissions. Monitor CAN Bus Load: Check the load on the bus using a CAN bus analyzer. Excessive bus load can also lead to signal integrity issues. Expected result: A bus load of less than 60% for optimal performance.

Conclusion:

Low signal integrity in TJA1043T/1J CAN transceivers can stem from a variety of causes, including improper PCB layout, incorrect termination, EMI, voltage issues, and poor wiring. By following the steps outlined above—reviewing the PCB layout, checking termination resistors, minimizing EMI, verifying voltage levels, and using proper wiring—you can address these issues and restore reliable CAN communication.

By conducting thorough testing and validation, you can ensure that the signal integrity is restored and that your CAN network operates smoothly and without errors.

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