SLLA636A June 2024 – August 2024 TCAN3403-Q1 , TCAN3404-Q1
Modern-day automotive systems provide a plethora of functions to help improve vehicle safety, performance and comfort. Design engineers create powertrains for advanced driver assistance systems, body electronics and lighting, infotainment and safety systems that include a large number of electronic control units (ECUs) to perform various electromechanical functions. ECUs exchange control and data-log information through in-vehicle network buses. Among network protocols such as Controller Area Network (CAN), Local Interconnect Network (LIN), FlexRay and Ethernet, the CAN bus remains the most popular choice given its ease of use, good common-mode noise rejection, priority-based messaging, bitwise arbitration to handle bus contention, and error detection and recovery features.
Until now, a majority of CAN transceivers deployed in vehicles have been based on a 5V driver and receiver supply. This is because the CAN physical layer (International Organization for Standardization [ISO] 11898-2:2024) and CAN component-level electromagnetic compliance (EMC) standard (International Electrotechnical Commission [IEC] 62228-3) provide specifications and pass/fail limits only for 5V-supplied CAN transceivers. There are subsystems that need a 5V power rail only for the CAN transceiver. A 3.3V-supplied CAN transceiver can simplify the power-stage designs of ECUs by eliminating the required 5V rail, while being fully interoperable with 5V CAN transceivers on the same network bus and meeting strict automotive EMC requirements. This white paper introduces TI’s TCAN3403-Q1 and TCAN3404-Q1 automotive-qualified and EMC-certified 3.3V CAN Flexible Data Rate (FD) transceivers.
All trademarks are the property of their respective owners.
With the electrification of vehicles happening at a rapid pace, multiple ECUs are deployed all through the vehicle. These subsystems talk to each other through a CAN network.
Figure 1-1 shows a CAN network.
Each CAN node consists of at least three components: a CAN transceiver, a microcontroller (MCU) or microprocessor (MPU), with an embedded CAN protocol controller and a power device (a DC/DC converter or linear regulator) that converts the automotive battery voltage to 5V. Additionally, in case the MCU or MPU’s input/output (I/O) voltage is 3.3V, a separate 3.3V power device is used on the ECU’s printed circuit board (PCB). Figure 1-2 shows a simplified schematic.
Typical CAN bus signals consist of dominant and recessive phases. A CAN driver produces a differential signal of at least 1.5V across a 60Ω load during the dominant phase, whereas the driver weakly biases the bus to a common-mode 2.5V level during the recessive phase. This signaling is designed for bitwise arbitration, and the device with the highest priority ID (the CAN frame identification field with the most dominant bits) takes control of the bus, since the dominant (strong) drive is able to overcome recessive (weak) biasing. The receiving nodes monitor CAN high and CAN low differential signals and can decode the CAN message as long as the signal is above 900mV (the dominant threshold) or below 500mV (the recessive threshold).
VD = VCANH – VCANL
For driver: VOD(DOM) ≥ 1.5V @ 60 Ω load
For receiver: VID(DOM) ≥ 900mV, VID(rec) ≤ 500mV
A CAN wiring harness is spread throughout the vehicle. Any common-mode disturbance generated by the CAN transceiver can result in emissions that can impact the functionality of other automotive subsystems. Similarly, the harness is susceptible to electromagnetic interference from other modules. Thus, electromagnetic compliance is an important requirement for any automotive CAN transceiver. Different subsystems can have CAN transceivers from different semiconductor vendors; thus, interoperability is another requirement for any CAN transceiver to be used in a mainstream vehicle network.