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TCAN4550: Termination resistance.

Kengo.Y
Guru 11245 points
Part Number: TCAN4550

Hi team,

I'd like to know how to select the resistance.(1/2W?,1/4W)
EVM used 0.5W resistance.

However, the maximum current is 100mA (Ios), and 2.4W is required for the communication line because it is a 24V power supply.

Could you tell me why it can use 0.5W resistance?

Sincerely.
Kengo.

  • 0
    TI__Guru 53555 points

    Hi Kengo,

    There's actually a lot to consider when selecting the power rating for termination resistors in CAN systems. While small values such as 1/4W are suitable for most normal operation, very conservative approaches may use 5W ratings to survive even the most extreme and prolonged fault conditions.  Since not all fault conditions in CAN systems are hard shorts to battery voltages, may not persist for long enough for resistor heating to cause damage, and may even be dependent on the ratio of dominant to recessive bits in the datastream, a system can still see considerable increase in reliability when only increasing the rating from 1/4W to 1/2W. Because of the benefits this increase offers and the fact that 1/2W resistors are readily available and do not radically impact design size, this is a typical recommended value from us. This is likely why it was included on the TCAN4550 EVM. 

    The E2E post linked below goes into detail on some of these points so I'll encourage you to reach through if your curious about specific conditions or calculation. 
    Wattage Requirements for CAN-Bus Terminating Resistor with SN65HVD233

    Let me know if you have any other questions about this topic or the linked post. 

    Regards,
    Eric Schott