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TCAN1043A-Q1: Common mode choke power loss in CAN transceiver circuit

Sradha Ajay
Prodigy 20 points
Part Number: TCAN1043A-Q1

Tool/software:

Hi,

We are having two CAN transceivers (TCAN1044ADRBRQ1 & TCAN1043ADMTRQ1) connected to the bus. Before the transceivers, a common mode choke & termination resistors are there in the circuit. For calculating the common mode choke power loss, i used the average short circuit current formula given in the transceiver datasheet.

1. For conduction loss part, rms current rating is used conventionally. How i can find the rms value of current flowing through the common mode choke in this particular example.

2. Considering the worst case scenario, i have taken %Transmit as 0.5, %Receive as 0.5, %DOM_Bits=0.9, %REC_Bits=0.1. Is this the right approach?

Please clarify.

Regards,

Sradha

  • 0
    TI__Expert 8427 points

    Hi Sradha,

    Can I ask what your goal is for calculating this current value?

    If your goal is just the worst case current through the CMC, then you can just assume the current value is I_OS(DOM) which is 100mA. 

    Regards,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Prodigy 20 points

    Hi,

    The goal is to carry out the stress analysis of the common mode choke.

    In the circuit, there is only one CMC connected to two CAN transceivers (TCAN1043ADMTRQ1 & TCAN1044ADRBRQ1). That is the two CAN transceivers are made parallel at the output side of CMC.

    For TCAN1044ADRBRQ1, I_OS(DOM) is around 115mA.

    For TCAN1044ADRBRQ1, I_OS(DOM) is around 100mA.

    For the worst case analysis, do i need to consider the sum of above two currents? (i.e, 215mA).

    Also for calculating the I^2R loss across the DC resistance of CMC, is there any RMS current value available?

    Regards,

    Sradha

  • 0 in reply to Sradha Ajay
    TI__Expert 8427 points

    Hi Sradha,

    Thank you for clarifying that.

    For the worst case, you would just need to pick the larger current value, which is 115mA. 

    There is no RMS current value as the CMC does not exhibit AC characteristics.

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Prodigy 20 points

    Hi,

    If two CAN transceivers are in dominant mode, the maximum bus current through CMC is the highest dominant current of two transceivers?

    Can you please explain me why summation is not applicable here.

    Regards,

    Sradha

  • 0 in reply to Sradha Ajay
    TI__Expert 8427 points

    Hi Sradha,

    Theoretically it could be a little higher than the IOS dominant current for a very short period when both devices are driving dominant, but due to CAN arbitration it will just be the dominant current of one device. Using just the single device's IOS dominant current will be good for estimating the worst case scenario. So 115mA will be good for your calculations. 

    Regards,

    Ethan