Overview
ISO 11898-3:2006 - "Road vehicles - Controller area network (CAN) - Part 3: Low-speed, fault-tolerant, medium-dependent interface" defines the physical-layer and fault‑tolerance requirements for low‑speed CAN links used in road vehicles. It covers CAN transmission rates above 40 kbit/s up to 125 kbit/s and specifies the Medium Dependent Interface (MDI) and Physical Medium Attachment (PMA) behaviours that enable distributed control and multiplexing between ECUs.
Key topics and technical requirements
- Physical medium: Two-wire pair (CAN_H and CAN_L), twisted or parallel, shielded or unshielded depending on EMC needs. Logical bus states are dominant and recessive using a differential voltage between CAN_H and CAN_L.
- Termination and network impedance: Overall termination resistance recommendations (network values typically around 120 Ω). Individual node termination must not be below 500 Ω; overall termination should be ≥100 Ω.
- Operating capacitance and timing: Methods to calculate operating capacitance from cable length, conductor-to-conductor and conductor-to-ground capacitances, node and plug capacitances. Timing equations (time constant τ, sample point, loop delays) are provided to derive maximum allowable capacitance and achievable bit rates.
- Electrical boundaries: ECU connection voltage tolerances specified for 12 V and 42 V systems (examples in the standard show surviving transients to approximately −27 V to +40 V for 12 V systems and up to ±58 V for 42 V systems).
- Fault tolerance and failure handling: Definitions of fault tolerance, bus/physical failures, and failure events. The PMA and transceiver behaviour under failures (including operating and low‑power modes, transceiver loop delay, and failure management) are specified.
- Layer scope: Focuses on the physical layer (MDI and PMA) and parts of the physical layer signalling (PLS) and medium access control (MAC) relevant to fault‑tolerant low‑speed CAN.
Applications and who uses it
ISO 11898-3:2006 is essential for:
- Automotive OEMs and vehicle system architects defining in-vehicle networks
- ECU and transceiver IC designers implementing low‑speed, fault‑tolerant CAN interfaces
- Wiring harness and connector designers calculating capacitance and termination
- Test labs and suppliers validating EMC, electrical tolerance and failure behaviour
- System integrators ensuring reliable body, comfort and diagnostics networks where reduced-speed, high-reliability CAN is required
Keywords: ISO 11898-3:2006, low-speed CAN, fault-tolerant CAN, MDI, PMA, automotive CAN transceiver, ECU, differential signalling.
Related standards
This part complements the broader ISO 11898 family by defining the medium-dependent and attachment requirements that make low‑speed CAN fault tolerant and robust for automotive applications.