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SN65HVDA1050A-Q1: Output impedance of the driver

Dice-K
Mastermind 7470 points
Part Number: SN65HVDA1050A-Q1
Other Parts Discussed in Thread: TPD2E007

Hello.

Please teach me the output impedance of the driver.

The reason why I want to know it is to check whether TPD2E007 with input capacitance of 15 pF can be used as a protection device of the communication line.

Regards,
Dice-K

  • 0
    TI__Intellectual 1895 points
    Hi Dice-K,

    I'll support you on your question. I'm probably will come up with an answer tomorrow morning.

    Kind regards
    Dierk
  • 0
    TI__Intellectual 1895 points

    Hi Dice-K,

    the CAN data transmission rate determines the maximum capacitance of the TVS device. A large capacitance on the data lines causes distortion in the signal waveforms. The distortion on the data lines is minimized by selecting a low capacitance TVS device.

    It is recommended that themaximum capacitance of the protective network measured from each signal line to ground should be less than 35 pF for 1.0 Mbits/s and 100 pF for 125 kbits/s.

    The TPD2E007 adds 15pF to each signal line to ground so its suitable to use with the SN65HVDA1050A-Q1 if you ensure to stay within the recommended range of total signal line to ground capacitance regarding the corresponding baud rate. 

    Let me know if this is answering your question.

    Kind regards

    Dierk

  • 0 in reply to Dierk Bronner
    Mastermind 7470 points
    Hello Dierk,
    Thank you for your reply.

    To summarize, is the answer as follows?

    There is not the data of the output impedance of the driver of SN65HVDA1050AQDRQ1.
    TPD2E007 with input capacitance of 15 pF can be used as a protection device of the 1Mbps communication line of SN65HVDA1050AQDRQ1.

    Best regards,
    Dice-K
  • 0 in reply to Dice-K
    Mastermind 7470 points
    Hi Dierk.

    Would you please let me know whether my answer above is correct?

    Best regards,
    Dice-K
  • 0 in reply to Dice-K
    TI__Guru 62920 points
    Hello Dice-K,

    (Dierk is out of the office this week, so I will address your question.)

    Yes, you are correct. When bus transitions from recessive to dominant, the change in voltage is driven across the load capacitance by the CAN driver (whose output impedance is typically in the range of 30-50 Ohms). When the bus transitions from dominant to recessive, the change in voltage across the load capacitance is driven by the termination resistance (60 Ohms). In either case, a load capacitance would result in a charge/discharge time that is very short compared to a bit period at 1 Mbps.

    One thing to consider in your analysis, though, is the number of nodes. The capacitance at each node will add on the total capacitance of the bus, and it is this total capacitance that will serve to limit the communication rate. For example, if you had 100 nodes at 15 pF each, the total capacitance would be 1.5 nF. With a 60-Ohm effective termination resistance, the time constant for CAN bus signals to go from dominant to recessive would be >500 ns. This would be too slow for reliable communication at 1 Mbps, but could work for slower rates.

    Please let me know if you have further questions.

    Regards,
    Max