SLLS983J June 2009 – September 2019 ISO1050
The device has several protection features that limit the short-circuit current when a CAN bus line is shorted. These include driver current limiting (dominant and recessive). The device has TXD dominant state time out to prevent permanent higher short-circuit current of the dominant state during a system fault. During CAN communication the bus switches between dominant and recessive states with the data and control fields bits, thus the short-circuit current may be viewed either as the instantaneous current during each bus state, or as a DC average current. For system current (power supply) and power considerations in the termination resistors and common-mode choke ratings, use the average short-circuit current. Determine the ratio of dominant and recessive bits by the data in the CAN frame plus the following factors of the protocol and PHY that force either recessive or dominant at certain times:
The short-circuit current of the bus depends on the ratio of recessive to dominant bits and their respective short-circuit currents. The average short-circuit current may be calculated with the following formula:
IOS(AVG) = %Transmit × [(%REC_Bits × IOS(SS)_REC) + (%DOM_Bits × IOS(SS)_DOM)] + [%Receive × IOS(SS)_REC]
Consider the short-circuit current and possible fault cases of the network when sizing the power ratings of the termination resistance and other network components.