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Original question:

TCAN332G: Application questions about TCAN332GD

TCAN332G: protection for Surge at CAN Bus lines

Olaf Altrock
Prodigy 10 points
Part Number: TCAN332G

To protect a TCAN332G CAN transceiver for surge test at the CAN-H and CAN-L lines we need a hint which TVS may be suitable.

The input range is limited to +/-14V. How it is internal protected? If we use a bidirectional TVS for 12V (common mode input range), voltages higher as 20V may occur during 8/20µs Surge test (IEC61000-4-5) with 500V test level. TVS for example is a SP4022-01FTG-C from Littlefuse.

Will the TCAN332G device be damaged?

A split termination will be present. Is a larger capacitance at the split termination to ground helpful to limit the peak voltages during surge test?

  • 0
    TI__Guru 50115 points

    Hi Olaf,

    An ideal protection diode would remain off within the common-mode input range of the transceiver (breakdown > 12V) but also clamp the voltage below the absolute maximum rating (clamp < 14V). This is a pretty tight and unreasonable range for a TVS diode, so I would recommend preferring the protection (clamp < 14V) and allowing for some leakage during non-nominal but acceptable conditions (breakdown > 6V). 

    The internal protection circuitry of TCAN332G is capable of protecting the device up to the ESD levels listed in datasheet section 8.2. Any conditions beyond these specifications will require external protection devices to ensure survival. Because you are testing for conditions beyond what is listed in the datasheet, external protection will likely be required. 

    Split capacitance primarily helps to filter common-mode noise, but will have limited effectiveness for transitents due to the series resistances from the termination resistors. Bus capacitors placed directly on CANH and CANL may help slow transient edges and marginally increase surge immunity. I typically recommend bus capacitor values between 10pF - 150pF depending on the size of the system (larger systems should use smaller bus capacitors to avoid overloading the CAN bus). 

    Lastly, I would like to advise against including series resistance in a CAN system. CAN is particularly sensitive to series resistance due to the relatively large current used to generate a dominant signal. Any series resistance will have a significant impact on attenuating this dominant signal and may degrade noise resistance or signal integrity. For device protection, active blocking components such as PTC fuses will be preferable as they have minimal impact on a nominally operating system. 

    Let me know if you have any questions on my response. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 10 points

    Hi Eric,

    thank you for your detailed answer.

    I found a suitable TVS diode array at SEMTECH: TClamp0602N.
    It is available for example at Mouser. There you can find the datasheet too.

    The breakthrough voltage is 6.8V and the protection level to ground is lower as 14V up to current flow about 15A. This is much more as during the surge test may flow.

    Since in large CAN-BUS systems ground fluctuation may be present, the TVS array cannot be used as the datasheet recommends. The protection must be performed from the pins 1,2,3 (CAN-L or CAN-H) to 8,9,10 (GND). The center tab should be left floating. Two parts must be used. One for each CAN line.

    The best thing is the parasitic capacitance is low about 15pF line to line.
    1MBaud will be possible with this protection.

    Regards

    Olaf Altrock