CAN bus split termination: What are typical component values?

Component values

The CAN bus split termination typically consists of three components:

• Two resistors of equal value. Typically these are 60Ω resistors, to obtain a total bus termination of 120Ω (this is the standard impedance for CAN cables). Typically, you would use 59.7Ω, 59.9Ω, or 60.4Ω resistors based on availability.
• One capacitor. This capacitor is usually in the range of 33nF to 100nF. Most designers use 47nF or 100nF capacitors. I recommend starting with 47nF.

Component ratings

The ratings depend on the worst case design assumptions:

• Conservative approach: Assume that one of the bus lines (CANH or CANL) is connected to the VCC rail (typically 12V or 24V, depending on the application), and the other line is connected to GND, i.e. a 12V or 24V differential voltage is applied across the bus lines.
• Optimistic approach: Assume that both bus lines are continously driven to dominant state, i.e. the voltage differential is 3.3V (if you ONLY use 3.3V-VCC CAN transceivers) or 5V (if you use ANY 5V-VCC CAN transceivers).

Resistor power

If you are unsure what selection to make, I recommend to use the 5V continous differential voltage as a basis.

• For 3.3V continous differential voltage: 45.4 mW for each resistor, this allows using even 0201 resistors with 0.05W power rating
• For 5V continous differential voltage: 104 mW for each resistor, this allows using some 0603 resistors with at least 0.125W power rating
• For 12V continous differential voltage: 600 mW of power for each resistor. While some special 1206 resistors can handle this, it is recommended to use at least 1210 resistors, or split the power over multiple parallel or series resistors.
• For 24V continous differential voltage: 2.40 W of power for each resistor. Typically you would use multiple resistors in parallel or in series to handle this power.

Capacitor voltage rating

The capacitor voltage rating should be at least 1.5x the maximum voltage that can be applied across the capacitor.

The voltage applied across the capacitor is the larger one of the CANH/CANL lines with respect to GND. In all practically relevant cases, this is the VCC rail voltage, i.e. the same voltage we used for the resistor power calculation.

• For 3.3V VCC: 6.3V capacitor voltage rating, this allows using 0201 capacitors.
• For 5V VCC: 10V capacitor voltage rating, this allows using 0201 capacitors.
• For 12V VCC: 25V capacitor voltage rating, this allows using some 0201 capacitors, but typically you would use 0402 or larger capacitors.
• For 24V VCC: 50V capacitor voltage rating, this allows using some 0402 capacitors but typically you would use 0603 or larger capacitors.

Code to compute resistor power:

from UliEngineering.Electronics.Resistors import *
from UliEngineering.EngineerIO import *
from UliEngineering.EngineerIO import print_value

print_value(power_dissipated_in_resistor_by_voltage(120.0, 3.3) / 2, 'W')
print_value(power_dissipated_in_resistor_by_voltage(120.0, 5.0) / 2, 'W')
print_value(power_dissipated_in_resistor_by_voltage(120.0, 12.0) / 2, 'W')
print_value(power_dissipated_in_resistor_by_voltage(120.0, 24.0) / 2, 'W')

Source: NXP AN10211