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[FAQ] CAN transceiver power consumption

Genius 13175 points

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How can the power consumption of a CAN transceiver in active operation be calculated?

Eric Hackett

Texas Instruments | INT-TRX| Applications Engineer

1 Reply

  • When calculating power consumption from a CAN transceiver on an active bus, several parameters must be known/assumed/measured. These parameters are:

    • Current consumption of the transceiver when the bus is in the recessive state
    • Current consumption of the transceiver when the bus is in the dominant state
    • Percentage of overall time the bus is in dominant vs. recessive state
    • Differential output voltage in the dominant state
    • VCC supply voltage
    • If the CAN transceiver has a VIO pin, the IO voltage and current will also need to be known.

    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)]

    And for transceivers with a VIO pin:

    P = [(1-D)*IREC*VCC] + [D*IDOM*(VCC-VOD)] + VIO*IIO

    • P is power
    • D is percentage of time the bus is in dominant state
    • VCC is the supply of the transceiver
    • IREC is the current consumption from VCC in the recessive state
    • IDOM is the current consumption from VCC in the dominant state
    • VOD is the output differential voltage of the bus in dominant state
    • VIO is the IO voltage of the device (if there is a VIO pin)
    • IIO is the IO current of the device

    As an example, we can use the TCAN1042 and assume 50% of the time in dominant state, and 50% recessive state.

    • VCC = 5V
    • IREC = 1.5mA
    • IDOM = 40mA
    • VOD = 2.25V
    • D = 0.5

    P = [(1-0.5)*1.5*5] + [(0.5)*40*(5-2.25)] = 3.75mW + 55mW = 58.75mW

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

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