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SN65HVD234-Q1: Differential input capacitance, common mode capacitance and common mode input resistance balancing

Clément Letonnelier
Expert 2426 points
Part Number: SN65HVD234-Q1
Other Parts Discussed in Thread: TCAN334, SN65HVD234, TCAN334G

Hello,

In our requirement specifications, we have to justify that we meet the following requirements for the can bus IO:

  • Differential input capacitance < 170pF
  • Common mode capacitance < 300pF
  • Common mode input resistance balanced one compared to other at +- 3%

So we need to take into account the data from the SN65HVD234-Q1 as well as the capacitance introduced by the tracks, the EMI filters and the TVS we have implemented for EMI/EMC and lightning protection (design for helicopters).

For the two first, the data sheet provides typical information but we need to justify it over the whole temperature range of the device.
What would TI suggest as a safe WCA estimation ? 10% ? 20% ?

For the third one, there is no info on the dispersion between the H and L inputs, do you have such data ?

Best regards,

Clément

  • 0
    TI__Guru 67002 points

    Clement,

    For the common-mode input resistance, it doesn't look like we included the number in this datasheet, but for our other 3.3V CAN transceivers (TCAN33x family) this is specified at +/-3%. Also, in the TCAN33x family, the bus capacitance is specified at a maximum of 20pF for common mode, and 10pF for differential, and I believe this is across all temperature ranges the device is qualified.

    For the information on the SN65HVD234, I'll have to dig a bit for that information as those are older devices. Is it possible to use the TCAN334 though? Or are there other requirements that don't allow this?

    Regards,

    Eric Hackett

  • 0 in reply to Eric Hackett
    Expert 2426 points

    Eric,

    We used that device because it was flagged Q1 but we didn't figure out the initial non Q1 version dated back to 2002 Sweat smile

    As we are developing equipments for the aeronautical field, we tend to pick Q1 devices as we value them as higher quality but it's not a strict rule.

    I don't see any particular reason why the TCAN33x family wouldn't fit, do you have any particular difference to highlight that we should be aware of ?

    Regards,

    Clément

  • 0 in reply to Clément Letonnelier
    TI__Guru 67002 points

    Clément,

    Thanks for the additional information. And yes, the SN65HVD234 devices are quite old, still regularly used, but old. 

    The one big difference between the two that may be a show-stopper is the CAN bus absolute maximum rating (voltage at which the pin will be damaged). On the SN65HVD234 device CANH and CANL are rated  from -36V to +36V. On the TCAN334, the rating is -14V to +14V, so it's a fairly significant difference. The TCAN334 is also available in a smaller SOT-23 package as well as the SOIC package that both are available in, and the TCAN334G can work above 1Mbps, where the SN65HVD234 is limited to 1Mbps.

    Let me know if any of these differences will be a problem in using the TCAN334. Also, can you give a bit more information about your application? I'm curious about what kind of equipment we are talking about. And if you do decide to share more information but don't want to put it on this public forum, you can email me directly.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Expert 2426 points

    Eric,

    The rating was an issue in our current design related to sustainment of the lightning agressions as we had 24V TVS but a change of the TVS pushes that issue away.

    The speed is not of interest for us, due to environment constraints we can't go higher than 500kbit/s.

    Regards,

    Clément

  • 0 in reply to Clément Letonnelier
    TI__Guru 67002 points

    Clément.

    Understood, please let us know if you have any other questions or concerns. For now, I will close this thread.

    Regards,

    Eric Hackett