# CAN BUS Termination resistor sizing

I am using ISO1042 CAN Transceiver to establish communication between my board micro-controller with other board controller separated by 0.5m distance. I am using standard 120 ohm termination resistance. I would like to size the resistor. For that I would like to estimate worst case power dissipation for the resistor. How can I do that?

Vcc1 of ISO1042 is 3.3V and Vcc2 is 5V.

The differential output voltage specification (in section 6.10 of the datasheet) says that the driver can generate a voltage drop of at most 3 V over the two termination resistors (2× 120 Ω in parallel). So the theoretical worst-case power dissipation in a single resistor during normal operation is (3 V)² / 120 Ω = 75 mW.

If you want to survive shorting the bus line(s) to some other voltage, you might need more.

• Thanks for the answer. If the bus is shorted to lets say 5V or 10V, could you please tell me how can i calculate the power dissipation of the termination resistor ? Commented Feb 27 at 16:55
• You have to know the voltages at both ends of the resistor.
– CL.
Commented Feb 28 at 7:54
• Could you please elaborate ? Commented Feb 28 at 11:47
• P = (V2 − V1)² / R
– CL.
Commented Feb 28 at 15:05
• Hi, In the datasheet its mentioned like the short circuit current is limited to 100mA by the transceiver IC. so in that case can i use P = I2*R = 0.1*0.1*120 to size the resistor ? Commented Feb 29 at 9:16