CAN Bus Termination Resistor

Formula

Description

CAN bus requires two termination resistors, one at each end of the bus, to prevent signal reflections. Each resistor is nominally half the cable characteristic impedance, so the two in parallel equal Z₀. Standard CAN bus cable has Z₀ = 120 Ω, so each termination resistor is 60 Ω. However, the ISO 11898 standard specifies 120 Ω at each end (not 60 Ω), because the bus is driven differentially and each termination bridges CAN_H to CAN_L. The parallel combination of two 120 Ω resistors provides the correct DC bias and AC termination.

Variables

• R_term — Termination resistor value at each bus end (Ω)
• Z₀ — Characteristic impedance of the CAN bus cable (Ω)

Practical Notes

Standard CAN: 120 Ω termination at each end of the bus. CAN FD uses the same termination. Split termination (two 60 Ω resistors with a capacitor to ground at the midpoint) provides better EMI performance by filtering common-mode noise. Missing or incorrect termination causes reflections, bit errors, and can prevent communication entirely. The total resistance measured between CAN_H and CAN_L with both terminators in place should be about 60 Ω.