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How can the power consumption of a CAN transceiver in active operation be calculated?
Texas Instruments | INT-TRX| Applications Engineer
When calculating power consumption from a CAN transceiver on an active bus, several parameters must be known/assumed/measured. These parameters are:
The current consumption of the transceiver in both states, and the amount of time the bus is in both states is fairly self-explanatory in this calculation. Because the current consumption in either state is significantly different, and the CAN bus state is consistently changing during communication, the amount of time the bus is in recessive vs. dominant state is going to factor heavily into the power consumption of the transceiver. The differential output voltage during dominant mode is necessary because some of the power consumed from the VCC supply will be through the termination resistance. Knowing the drop across this resistance will determine how much current is being consumed through that resistance. The differential output voltage during recessive mode isn't necessary because there should not be a significant (or any at all) voltage drop across the resistor when the bus is recessive; CANH and CANL should be within tens of millivolts of each other, if not the same exact voltage.
The formula for power consumption after knowing all of these variables is:
P = [(1-D)*IREC*VCC] + [D*IDOM*(VCC-VOD)]
For transceivers with a VCC and VIO pin:
P = [(1-D)*IREC*VCC] + [D*IDOM*(VCC-VOD)] + VIO*IIO
And for transceivers with a VCC, VIO and VSUP pin (like TCAN1043):
P = [(1-D)*ICCREC*VCC] + [D*ICCDOM*(VCC-VOD)] + [(1-D)*VIO*IIOREC] + (D*VIO*IIODOM) + VSUP*ISUP
As an example, we can use the TCAN1042 and assume 50% of the time in dominant state, and 50% recessive state.
P = [(1-0.5)*1.5*5] + [(0.5)*40*(5-2.25)] = 3.75mW + 55mW = 58.75mW
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