• State TI Thinks Resolved
  • Locked Locked
  • Replies 13 replies
  • Answers 4 answers
  • Subscribers 32 subscribers
  • Views 3460 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

TCAN1042-Q1: Why are TCAN series the 5V only?

TCAN1042-Q1: The TVS on the front end of SM712 is damaged

user5273056
Prodigy 210 points
Part Number: TCAN1042-Q1
Other Parts Discussed in Thread: TCAN1042H,

The front-end TVS used in the design are SM712, and there will be D4 damage. However, after replacing D4, the fault will be solved.The circuit diagram is shown in the figure

  • 0
    TI__Guru 62910 points
    Hello,

    Is it possible that the CANH/CANL lines were shorted to a voltage greater than the breakdown voltage of the TVS? That's the most common cause of TVS failure that I have seen in CAN bus applications. In that case the solution may be to choose a TVS with higher breakdown voltage range. (The +/- 70 V rating of the TCAN1042H means that there should be plenty of margin to increase the TVS voltage if needed.)

    It is also possible for the TVS to be damaged by large transient surges. Do you think this might have occurred? If so, the solution would be to use a TVS with a higher peak power rating.

    By the way, you can read more about TVS selection for interface circuits in this blog:

    e2e.ti.com/.../how-to-choose-a-tvs-diode-for-rs-232-rs-485-and-can-based-on-voltage-ratings

    Please let us know if you have further questions.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Prodigy 210 points
    thanks
    What is the limit voltage input of CANH and CANL for TCAN1042H? What is the model or parameter used for TVS at the front end of TCAN1042H reference design?
  • 0 in reply to user5273056
    TI__Guru 62910 points
    The maximum voltage supported by TCAN1042H on the CANH/CANL pins is +/- 70 V. The internal ESD protection will not activate until above this level (~80 V).

    Max
  • 0 in reply to Max Robertson
    Prodigy 210 points
    thanks
    Could you please tell me the type of TVS on the EVM board of TCAN1042H, or what the Vc and maximum Vrwm parameters for TVS(D4) at the front end of this circuit design should be
  • 0 in reply to user5273056
    TI__Guru 62910 points

    The EVM layout was designed to support any dual bidirectional TVS in SOT-23 package.  PESD1CAN is a very common one that would fit this board.  In general, though, any TVS can be chosen based on the following characteristics:

    - Power rating that is appropriate for the transient immunity level required by the application

    - Vrwm greater than the maximum voltage expected in the application.  (For CAN it is expected for the signal lines to operate over a +/- 12 V range.  Additionally, higher-voltage support is often needed in automotive applications to protect against short-circuits to battery lines.)

    - Peak clamping voltage less than the maximum pin rating (in this case 70 V).

    Regards,
    Max

  • 0 in reply to Max Robertson
    Prodigy 210 points
    thanks
    Is it inappropriate to use SM712 for the design of D4? If the TVS of TI are selected, what model should be selected for the front end
  • 0 in reply to user5273056
    TI__Guru 62910 points
    No, SM712 would not be inappropriate. One potential drawback is that the working voltage range only extends down to -7 V. This is good for RS-485 interfaces (since it aligns with the operating common mode range specified by TIA/EIA-485), but some CAN applications are specified to operate over a wider range.

    If these diodes are getting damaged, though, it would be good to understand why. If they experienced DC stress beyond their reverse breakdown voltage, then the solution would be to select a higher-voltage TVS. If the TVS diodes were damaged by large transient energy, then the solution would be to select a TVS with high peak power rating.

    Max
  • 0 in reply to Max Robertson
    Prodigy 210 points
    Now according to the blog you provided before, I suggest to select TVS with a higher voltage clamping, but at present, it is still in the state of selection. Do you have any good Suggestions?
  • 0 in reply to user5273056
    TI__Guru 62910 points
    What is the highest voltage you expect on the CANH/CANL lines, either during normal operation or during a fault condition? (In many applications there is a need to protect against a short-circuit to a power supply, and so the power supply voltage would determine the worst-case bus voltage.) I would recommend picking a TVS diode with working voltage range a little bit larger than you plan to encounter. There is an SMAxxx series of diodes available from several different manufacturers (Bourns, Littelfuse, etc.) that are good for most applications. They are rated to 400 W, and if higher power is needed you could try the SMBxxx (600 W) or SMCxxx (1500 W) options - this will depend on the severity of transients encountered by your system. The PESD1CAN TVS I mentioned earlier is also very commonly used in these applications since it is marketed specifically for CAN (and has a working voltage range that would be suitable for 12-V automotive applications).

    Max
  • 0 in reply to Max Robertson
    Prodigy 210 points
    Hi Max，
    The maximum voltage of VRWM of PESD1CAN is 24V, but the maximum voltage of CAN we choose is 70V. In this case, is it not suitable for PESD1CAN? Why we choose it on the demo board?The voltage on the CANH and CANL of the original design plan is around 48V. According to your experience, what are the better TVS recommended according to such design requirements, and it is better to be TI.
  • 0 in reply to user5273056
    TI__Guru 62910 points
    It is important for the maximum voltage of the transceiver to be larger than the peak clamping voltage of the TVS. So, using a 24-V TVS with a 70-V transceiver is good. A higher-voltage TVS could likely be used as well, but I don't see much of a benefit to this. For a given surge current, a higher-voltage TVS will have larger power dissipation than a lower-voltage TVS, and so the device may need to be larger or more expensive to maintain the same immunity performance.

    The drawback to reducing the TVS voltages is that it reduces the usable operating voltage range of the system. Most CAN buses are specified over a +/-12 V operational common mode range, though, and so a 24-V TVS would not introduce any limit on operation.

    I hope this is all clear; please let me know if you have further questions.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Prodigy 210 points
    hi MAX
    thanks
    Thank you for your advice, according to your opinion, before using SM712 comply with the design requirements, but is there a clamping voltage close to the working voltage of the situation, there will be damaged, now understand that the original design CANH and CANL voltage around in 48 v, if this is the case before you recommend TVS diode should be accord with the requirement of design, if it is for this design do you have any Suggestions, now I also in finding suitable TVS diode, but has not found the right
  • 0 in reply to user5273056
    TI__Guru 62910 points
    Do you mean that the DC voltage on the CANH and CANL pins could be as high as 48 V in this application? In that case, then I agree that a TVS working voltage greater than 48 V is needed. These can be more challenging to find. SMF45A would be one example, although its rating is only 200 W - I'm not sure if this is large enough. You may want to contact some TVS diode vendors to see what kind of solution they would recommend.

    What is your target for ESD protection? The TCAN1042-Q1 already has a very high level of ESD immunity - have you evaluated whether this device could be used without a TVS in your application? (We have done a lot of characterization on this device and found that it is able to meet the most common customer ESD requirements without requiring additional components.)

    Another strategy would be to place a capacitor in series between the TVS diode and the CANH/CANL lines. This would allow fast transients like ESD to be clamped by the TVS but a DC short-circuit to be blocked. This would allow a lower-voltage diode to be used.

    Max