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TCAN3414: 8Mbps compatibility and 3.3V tradeoffs

Nino Abundes
Prodigy 30 points
Part Number: TCAN3414
Other Parts Discussed in Thread: TCAN3413, SN65HVD233, TCAN332, TCAN3403-Q1, TCAN3404-Q1, TCAN3404

Hello,

I am looking for a new CAN transceiver for a new from scratch design. Since I last looked at CAN many years ago, there are higher speed devices and devices that run on 3.3V that are interesting.

TCAN3414 is an example. It appears to run solely off a 3.3V supply and support up to 8Mbps CAN FD. I have the following questions:

  1. The datasheet specifically says "up to 8 Mbps operation in simpler networks is possible with these devices." There is no further mention of what this exactly means. What is the threshold on a simpler network vs less simple networks? Can this chip work at 5Mbps for all other networks then?
  2. I don't have a 5V supply in my system so using 3.3V is intriguing to me. Section 8.3.1.4 of the datasheet suggests the only difference between a 3.3V device and a 5V device is the recessive common mode voltage, but it seems that is still within the ISO CAN spec. However, there are much fewer 3.3V systems on the market. I am curious if there are other tradeoffs that aren't mentioned here? Is it just a legacy thing, or if I care a lot about performance, I should consider 5V?
  3. I have read app note SLLA337 and I am trying to weigh the cons of interoperability between 3.3V and 5V as well. If we have a common ground system with two CAN nodes talking to each other (one at 3.3V and one at 5V), it seems to me that there will be common mode current flowing from the 5V node to the 3.3V node in both the recessive state and states where 5V is trying to dominate. As we alternate between those two states and the 3.3V dominant state, the common mode current would alternate. I presume there is voltage division going on inside the chip to allow for a wide common mode range. Does that mean these common mode currents are small? Or is this a valid concern?

Thanks!

  • 0
    TI__Mastermind 23945 points

    Hi Nino,

    Thanks for reaching out!

    The two primary considerations for CAN communication are the transmitter and the bus. The CAN transmitter itself has some maximum rate that it can communicate on an "easy" bus or with very little loading. This is usually what you'll see shown in data sheets, since it represents the actual capability of the transceiver. By standard, transceivers are generally 5 Mbps capable in an ideal environment. What you're reading in the data sheet for TCAN3413 indicates that this transceiver slightly exceeds that industry standard and can transmit/receive up to 8 Mbps in ideal or light loading conditions.

    The bus, on the other hand, is the second limiting factor. As the bus gets heavier or more complex, it lengthens the time it takes for the dominant-to-recessive edge of the CAN waveform to fall back to logic 1. As ringing or capacitance increase this fall time, it reduces the maximum communication rate of the bus, regardless of the transceiver's maximum capability.

    Unfortunately, determining the maximum speed of a CAN bus is not an exact science and there generally aren't very many easy ways to do back-of-the-napkin analyses to determine maximum speed. Many network designers implement this by actually creating the cable harness or bus that they plan on using, and then they execute testing with real transceivers on the bus to determine their maximum achievable speed in that architecture. While there are some new simulation models that are being developed more recently, they have not quite yet become fully established as replacements to real-world testing.

    In an industrial environment, 3.3V CAN has existed for a while for exactly the reasons you listed. Since receivers don't care about the actual common-mode of a signal but rather just care about the differential voltage, they should be interoperable. In industrial systems they've existed for a while, which has allowed designers to get rid of the 5V rail. The new family of TCAN34xx(-Q1) devices are designed for improved performance compared to the prior generation (TCAN33x) and even achieve electromagnetic capability performance that allows them to be used in automotive applications. Previously, this was the barrier to use in most automotive CAN systems, but TI's recent developments in 3.3V CAN technology have shown that it is achievable, and now the international standards bodies have begun formally adopting this into international standards.

    And lastly, regarding your question of SLLA337, while the information in it is correct, it is current as of 2013, at which time we only had SN65HVD233 and its associated family on the market, which is two generations before TCAN3413 (I'm considering the TCAN332 and associated family as the generation in-between). To specifically address your questions, when a transceiver is recessive or not transmitting, it is largely high-impedance to the bus, so it shouldn't be sourcing/sinking much current. So though your concern is certainly valid, it has been considered when designing for 3.3V CAN transceivers.

    In general, the top three considerations for developing this family were:

    1. Is there a market need for 3.3V CAN?
      1. Yes - this has been established for a while as it allows designers to move away from 5V LDOs/SMPSs.
    2. Is 3.3V CAN interoperable with 5V CAN transceivers on the same bus?
      1. Yes - this also has been known for a while but was not too much of a shock or concern since the differential voltage requirements were being met by both transmitters and receivers for 3.3V and 5V CAN.
    3. Do mixed/heterogeneous networks perform well together, just like homogeneous networks?
      1. Yes - this is the newer breakthrough. The TCAN3403-Q1 automotive family passes requirements for electromagnetic compatibility, a concern previously not considered achievable. For the TCAN3414 industrial counterparts, they've been designed to target these same concerns while optimizing cost and performance.

    Best,

    Danny 

  • 0 in reply to Danny Bacic
    Prodigy 30 points

    Hello !

    Thank you for a very thorough response! You have to be careful being so helpful because now I want to ask you more questions haha!

    What new EMC performance spec has the TCAN34xx(-Q1) greatly improved on?

    Also your final point implies that TCAN3403-Q1 is better than TCAN3414 because the latter optimizes cost. The TCAN3403-Q1 is still in preview but the website suggests it is cheaper than TCAN3414. The TCAN3403-Q1 also has a lower common mode input voltage range. Other than than automotive rating, what specs does the TCAN3403-Q1 improve on that one would consider trading the lower common mode input voltage range? Or if I don't have an automotive application, should I just go with TCAN3414?

  • +1 in reply to Nino Abundes
    TI__Mastermind 23945 points

    Nino,

    Please always feel free to ask questions. I appreciate the sentiment. Slight smile

    The issue with interoperating 5V and 3.3V CAN devices on the same bus is that the common mode of the 3.3V transmitter(s) is different from that of the 5V transmitter(s). In older devices, this varying common-mode is what contributes to increased emissions characteristics. Our newer family shapes the 3.3V waveform in such a way to reduce or eliminate this concern.

    Nino Abundes said:
    Also your final point implies that TCAN3403-Q1 is better than TCAN3414 because the latter optimizes cost.

    Let me clarify. Our TCAN34xx family includes the TCAN3403-Q1, TCAN3404-Q1, TCAN3413, and TCAN3414. This entire family is cost-optimized compared to its prior generation, which was the TCAN33x family. The newer TCAN34xx family is produced on an optimized process technology, newer than the process used to produce the TCAN33x portfolio. This is what allows for both cost and performance optimization; I did not intend to imply that it's particularly a difference between TCAN3403-Q1 and TCAN3414.

    For the -Q1 devices, the added benefit is the AEC-Q100 qualification. If this is not needed for your application then the TCAN3413/TCAN3414 should be good for your needs.

    Best,

    Danny

  • 0
    Prodigy 30 points

    Is there an estimate when the other packages of the TCAN3414 will be available? I would like to use one of the smaller packages. It seems the datasheet doesn't even have the VSON package drawing yet. 

  • 0 in reply to Nino Abundes
    TI__Mastermind 49975 points

    Hi Nino,

    The TCAN3414 will be available in the SOIC, VSON, and SOT packages. The current datasheet preview on TI.com includes summary information for these on the first page. The detailed drawings and land patterns near the end of the document look like they need to be updated to include the VSON information. In the meantime, you can reference the drawings on pages 13-15 of the TCAN3404 datasheet preview as these packages are the same:
    https://www.ti.com/lit/ds/symlink/tcan3404-q1.pdf 

    Regards, 
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 30 points

    , is there an anticipated release date for the other packages? I see they are still in pre-production, and one cannot even purchase pre-production SOT-23 packages.

  • 0 in reply to Nino Abundes
    TI__Mastermind 23945 points

    Nino,

    Currently the TCAN3413/TCAN3414 is expected to completely release a little bit before the TCAN3403-Q1/TCAN3404-Q1 as the latter pair needs additional qualification related to AEC-Q100. Specifically, we are expecting the TCAN341x pair to fully release within the next month or so, while the TCAN340x-Q1 pair will release closer to midyear around the end of the second quarter of 2024.

    Best,

    Danny