How to Use TJA1021: Examples, Pinouts, and Specs

The TJA1021 is a high-speed CAN (Controller Area Network) transceiver manufactured by NXP. It is designed for automotive applications, enabling robust and reliable communication between microcontrollers and CAN networks. The TJA1021 is compliant with ISO 11898-2 and ISO 11898-5 standards, making it suitable for a wide range of automotive and industrial applications.

• Automotive in-vehicle networking (e.g., engine control units, body control modules)
• Industrial automation systems
• Electric vehicle (EV) battery management systems
• Diagnostic tools and equipment
• Communication between embedded systems in harsh environments

The TJA1021 is available in an 8-pin SO8 package. Below is the pinout and description:

1. Power Supply: Connect the Vcc pin to a regulated 5 V power supply and the GND pin to the system ground.
2. CAN Bus Connection: Connect the CANH and CANL pins to the respective high and low lines of the CAN bus.
3. Microcontroller Interface:
   • Connect the TXD pin to the microcontroller's CAN transmit pin.
   • Connect the RXD pin to the microcontroller's CAN receive pin.
4. Mode Selection:
   • Use the S pin to select the operating mode:
     • High: Normal mode (active communication).
     • Low: Standby mode (low power consumption).
5. Enable/Disable: Use the EN pin to enable or disable the transceiver.

• Termination Resistor: Ensure a 120 Ω termination resistor is present at each end of the CAN bus for proper signal integrity.
• ESD Protection: While the TJA1021 has built-in ESD protection, consider adding external TVS diodes for additional protection in harsh environments.
• Power Supply Decoupling: Place a 100 nF ceramic capacitor close to the Vcc pin to filter noise and stabilize the power supply.
• Signal Integrity: Keep the CANH and CANL lines as short as possible and use twisted-pair cables to minimize electromagnetic interference (EMI).

Below is an example of how to interface the TJA1021 with an Arduino UNO using the MCP2515 CAN controller library:

#include <SPI.h>
#include <mcp_can.h>

// Define the SPI CS pin for the MCP2515 CAN controller
#define CAN_CS_PIN 10

// Initialize the MCP2515 CAN controller
MCP_CAN CAN(CAN_CS_PIN);

void setup() {
  Serial.begin(115200);
  while (!Serial);

  // Initialize the CAN bus at 500 kbps
  if (CAN.begin(MCP_ANY, CAN_500KBPS, MCP_8MHZ) == CAN_OK) {
    Serial.println("CAN bus initialized successfully!");
  } else {
    Serial.println("CAN bus initialization failed!");
    while (1);
  }

  // Set the CAN controller to normal mode
  CAN.setMode(MCP_NORMAL);
  Serial.println("CAN controller set to normal mode.");
}

void loop() {
  // Example: Send a CAN message
  byte data[8] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08};
  if (CAN.sendMsgBuf(0x100, 0, 8, data) == CAN_OK) {
    Serial.println("Message sent successfully!");
  } else {
    Serial.println("Error sending message.");
  }

  delay(1000); // Wait 1 second before sending the next message
}

1. No Communication on the CAN Bus:

   • Verify that the TXD and RXD pins are correctly connected to the microcontroller.
   • Check the termination resistors on the CAN bus.
   • Ensure the S pin is set to the correct mode (Normal mode for communication).

2. High Power Consumption in Standby Mode:

   • Ensure the S pin is set to low for Standby mode.
   • Check for any leakage currents in the circuit.

3. Data Corruption or Noise on the CAN Bus:

   • Use twisted-pair cables for the CANH and CANL lines.
   • Verify that the 120 Ω termination resistors are properly installed.
   • Add external filtering capacitors if necessary.

4. Overheating of the TJA1021:

   • Ensure the supply voltage does not exceed 5.5 V.
   • Check for short circuits on the CANH and CANL lines.

Q: Can the TJA1021 operate at 3.3 V?
A: No, the TJA1021 requires a supply voltage between 4.5 V and 5.5 V. It is not compatible with 3.3 V systems without a level shifter.

Q: What is the maximum cable length supported by the TJA1021?
A: The maximum cable length depends on the data rate. For example, at 1 Mbps, the maximum length is approximately 40 meters. For lower data rates, longer cable lengths are possible.

Q: Is the TJA1021 suitable for non-automotive applications?
A: Yes, the TJA1021 can be used in industrial and other embedded systems requiring CAN communication.

Q: How do I protect the TJA1021 from voltage spikes?
A: Use external TVS diodes and proper grounding techniques to protect the transceiver from voltage spikes and surges.