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Original question:

[FAQ] CAN transceiver power consumption

TCAN4551-Q1: Formula for power consumption for devices with VIO and VSUP pin only

Marvn Arcangel
Genius 12970 points
Part Number: TCAN4551-Q1


Hi Team,

I am calculating the CAN transceiver power consumption of TCAN4551-Q1 using this FAQ (https://e2e.ti.com/support/interface-group/interface/f/interface-forum/823824/faq-can-transceiver-power-consumption)

However, the device only has a VIO and VSUP pin and could not use the formula highlighted below. Can you please clarify how can I proceed? 

Thanks!

Regards,

Marvin

  • 0
    TI__Guru 53575 points

    Hi Marvin,

    The TCAN4551 has an internal LDO that derives a 5V rail for the CAN transceiver from the Vsup supply. The specifications for Isup in the datasheet reflect the current of this 5V rail for the CAN driver in various states. Use these values in place of the Vcc values on the listed calculations to get the power consumption of this SBC from the Vsup and Vio supplies. 

    Note if you are doing power calculations for thermal considerations, be sure to factor in the voltage drop from the LDO as thermal energy added to the IC itself. 

    Let me know if you have any more questions. 

    Regards, 
    Eric Schott 

  • 0 in reply to Eric Schott1
    TI__Genius 12970 points

    Hi Eric,

    The customer used the below formula for estimating the power dissipation and thereby finding the junction temperature. But the calculated Tj is greater than 150 Deg C. 

    please note that the load resistance is 50 ohms.

  • 0 in reply to Marvn Arcangel
    TI__Guru 53575 points

    Hi Marvin,

    The most significant part of the calculation listed here the Vsup_typ * Idom portion. Using the values listed here, this accounts for 1.44 Watts of the total calculated value. This portion does not account for the 50% dominant time estimation nor does it assume any of the power will be dissipated externally by termination resistors. This portion also includes all of the power that has been previously calculated as it multiplies the whole voltage drop across all previous circuits (we've already accounted for the voltage drop across the CAN driver with the Vcc calculations). 

    This last variable (Vsup_typ * Idom) should be changed to the following to accurately represent the power dissipated by the 5V LDO when deriving the Vcc supply from Vsup under dynamic loading conditions:
    ... + (Dcan * (Vsup_typ - Vcc) * Idom) + ((1-Dcan) * (Vsup_typ - Vcc) * Irec)

    This calculation will yield a much lower power requirement for the LDO of around 580mW (vs the 1440mW). The total power dissipation would then come to around 700mW for a junction temperature of ~25C above ambient (using only the RthetaJA estimation). 

    Where did the values for Ta(max) and Tint_heat come from? TCAN4551 does not specify a max ambient operating temperature. 

    Regards, 
    Eric Schott