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TCAN1042-Q1: common mode choke requirement for this IC

smita wale
Prodigy 30 points
Part Number: TCAN1042-Q1
Other Parts Discussed in Thread: TCAN1051-Q1, TCAN1051

Currently we are using TJA1051T/3 IC but it requires big common mode choke. we have a size constraint on PCB, could you please confirm that whether TCAN1042-Q1 requires common mode choke?what are the other filters and circuits required for this IC so that this IC will not have a EMC problem also.

  • 0
    TI__Guru 62910 points

    Hi Smita,

    Whether or not a choke is required depends on the EMC performance of the transceiver (e.g., how well-balanced the CANH/CANL differential signals are), the performance of the PCB/cabling (e.g., whether or not they result in differential-to-common-mode conversion due to things like line imbalance and the degree to which they may radiate at different frequencies), and of course the EMC requirements for the application.  We've found that the TCAN1042-Q1 (and TCAN1051-Q1, which would be more directly comparable to the part number you mentioned) is able to meet most common automotive EMC requirements without use of a choke.  (Specifically, this has been determined for the SAE J2962 and IEC 62228 requirements that are referenced by many automotive OEMs.)  You can read more about that in this white paper:

    http://www.ti.com/lit/wp/slly020/slly020.pdf

    One thing that can help at the PCB level to improve performance is the use of "split" termination.  This is mentioned in the TCAN1042/TCAN1051 datasheets, but you could read more about it here:

    https://e2e.ti.com/blogs_/b/industrial_strength/archive/2016/11/17/how-termination-can-improve-emc-performance-in-a-can-transceiver

    It is also common practice to install some filter capacitances from CANH/CANL to ground at each node in order to provide additional low-impedance paths for high-frequency noise or transients.  Example values might be 100 pF, although this should be scaled based on the number of nodes in parallel and the desired data rate.  (Capacitive loading can introduce timing distortion on the CAN bus, so it should be limited for higher CAN FD rates like 5 Mbps.)

    I hope this is clear, and please let us know if you have any questions.

    Regards,
    Max