Power Dissipation Calculation for CAN interface

Hello,

  I'm not specifically aware of an available app note on calculating the power dissipation for the CAN transceivers, but this would be a good topic for one in the future.

  In the mean time, here are some comments which hopefully would help you perform this calculation.

The datasheet lists the supply current under different operating conditions.  Depending on the mode of operation for the transceiver, the power dissipation may be simply the input supply current times the supply voltage which will be the case when the part isn't actively driving a load.  Standby and recessive states are 2 examples.  Note that the ADM3055 has 2 supply inputs, the ICC which powers the isolated supply and IIO which powers the input side isolator IC.

When the part is actively driving the CAN bus, then a portion of the input power is being absorbed by the CAN bus/terminating resistor and is not dissipated by the the transceiver.  The amount of this power is going to depend on the bus activity and ratio of dominant to recessive.  For this operational mode I'd suggest using the ICC current at the closest speed to calculate the input power and then subtract off the expected output power, Pbus. 

Pbus can be estimated by using the VOD for the CAN bus load range (see datasheet's Driver section), the effective CAN bus termination load and the assumed dominant to recessive ratio:  Pbus = (Tdominant/(Trecessive+Tdominant)) * (VOD^2) / Rbus.

If there is a load connected to the AUXout pin, then you can calculate that load's power and subtract that off as well.

If you have the circuit built up, instead of using the datasheet, you can measure the input voltage, currents and VOD as well as using the actual bus load with above calculations to get a more accurate estimation.

Eric

Thank you so much Eric