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The difference of TCAN1042 and SN65HVD230（VP230）

David zhang
Prodigy 60 points

Other Parts Discussed in Thread: SN65HVD230, TCAN1042G-Q1

The problems our OBD encountered on Honda cars are as follows:

1. Our device uses TCAN1042 as a transceiver ，If increase the resistance of 120 ohms,  then it can communicate with the car normally.

2. Our equipment uses TCAN1042 as the transceiver without increasing the 120 ohm resistance, but adding an extension cable between the device and the car (only the obd extension cable) can also communicate with the car normally.

3. Our equipment uses SN65HVD230 (VP230) as the transceiver (without 120 ohm resistor) can also communicate with the car normally.

Therefore, we want to know what is the electrical difference between TCAN1042 and SN65HVD230 (VP230).

Therefore, we want to know what is the electrical difference between the TCAN1042 and the SN65HVD230 (VP230). How to solve the problem of using the TCAN1042 as a transceiver (without adding a 120 ohm matching resistor), because most cars cannot solder 120 ohm matching resistors.

  • 0
    TI__Guru 53535 points
    Hi David,

    The CAN protocol operates using sending "dominant" and "recessive" signals on a bus. After a dominant is driven, the bus must fall back to a recessive state. Termination resistance is added to the bus to allow the two bus lines to reach an equivalent state when not being driven. Without termination on the bus, the dominant to recessive edges could be very large and may greatly reduce operating speeds. For this reason, it is important to include termination on CAN buses.
    The value of the termination resistance should be as close to the characteristic impedance of the cable (generally 120-Ohms) as possible to reduce signal reflections and maintain signal integrity.

    I have a few questions to help understand the situation:

    The TCAN1042 operates normally when terminated with 120-Ohm. Where is this termination being applied?
    The TCAN1042 operates normally when not terminated but connected to an extension cable. Is this cable terminated at some point?
    The SN65HVD230 operates normally when not terminated or connected to an extension cable. This may be due to a difference in the internal biasing network in this device that could allow it to operate more effectively in an unterminated environment than the TCAN1042, but it is still not ideal.

    In what case are either of these devices unable to communicate with the car and what is your desired implementation?
    Any more information that you can share about your system would also be helpful.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    Prodigy 60 points
    TCAN1042 is a high-speed CAN transceiver, but SN65HVD230 is a low speed CAN transceiver？
  • 0 in reply to David zhang
    TI__Guru 53535 points
    Hi David,

    The SN65HVD230 is designed for CAN signals with data rates up to 1Mbps.
    The TCAN1042 supports Classic CAN and CAN FD up to 2Mbps. Models that have a 'G' suffix (i.e. TCAN1042G-Q1) are designed to support up to 5Mbps.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    Prodigy 60 points

    What is the appropriate capacity of the filter capacitor C115 and C116?

    What is the appropriate capacity of the filter capacitor C112?

    See the attachment in detail。

    TCAN1042_SCH.docx

  • 0 in reply to David zhang
    TI__Guru 53535 points
    Hi David,

    Bus filter capacitors (C115 and C116) are typically in the range of 20pF - 60pF. Using large capacitors (such as the 470pF in the schematic) could considerably slow the edges of the signal. What data rate are you planning on driving in this system? The resistors in series with these (R282 and R283) are not typical. Are you trying to filter out any particular noise?

    The split tap capacitor (C112) is generally 4.7nF. When using 60-Ohms for each resistor in the split termination (R279 and R280), the RC circuit filters out much of the high frequency common mode noise on the line.

    Let me know if you have any other questions.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    Prodigy 60 points

    The attachment is the signal waveform of the CAN BUS we have tested

    Is there a problem in the signal？

    TCAN1042_CAN_BUS_WAVE_3.pdf

  • 0 in reply to Eric Schott1
    Prodigy 60 points
    What data rate are you planning on driving in this system?
    500K, the highest 1M。
    The resistors in series with these (R282 and R283) are not typical. Are you trying to filter out any particular noise?
    Our device is used in cars, so it is to filter out the noise on the CAN bus of car.
  • 0 in reply to David zhang
    TI__Guru 53535 points
    Hi David,

    I don't see anything abnormal in the bus waveform. Is there a problem in the data you're recieving? If so, could you provide a waveform from the Rx pin on the device to help debug?

    At speeds of 1Mbps, bus capacitance could slow your fall times enough to cause glitches. To avoid this I would recommend lowering the value of the filter capacitors on the bus (C115 and C116) as referenced in the previous reply.

    Regards,
    Eric
  • 0 in reply to Eric Schott1
    Prodigy 60 points
    So if we change (C115 and C116) to 68PF or 100PF, which value do you recommend?
  • 0 in reply to David zhang
    TI__Guru 53535 points
    Hi David,

    These capacitors are typically in the range of 20pF - 60pF to filter out noise while not adding too much bus capacitance that could lengthen signal edges. 68pF would fit this application. If you're anticipating long cable lengths that could increase bus capacitance, you may want to consider a smaller value.

    Regards,
    Eric