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SN65HVD230: RS pull down resistor value

Harry Ma
Intellectual 2610 points
Part Number: SN65HVD230

Hi Team

Customer is using CAN transceiver SN65HVD230 encountered the problem,  bus failure rate is relatively high.

The scenario is： 500K baud rate, the 8-pin RS is pulled down to ground by 20KΩ, the CAN bus is easy to be interference, the failure rate is more than 1%, and the report  CRC incorrect.  After pulling pin 8 down to 0Ω, the failure rate is significantly improved.

So, they would like to ask if you has encountered similar problems. and 

  • 1. When the RS pin is pulled down to the ground, why does it have an anti-interference effect?
  • 2. what's the root cause of the failure caused by RS using 20K pull-down ?
  • 3. When RS is pulled down to the ground, what precautions should be taken when applying it?
  • 0
    Guru 316940 points

    A resistor on pin 8 slows down the driver's edges (see section 10.4.2). This is helpful to prevent EMI at low data rates, but it appears that the edges were too slow for your data rate.

    You can use a resistor if it is small enough; check the waveform (at all receivers) with an oscilloscope.

  • 0 in reply to Clemens Ladisch
    TI__Guru 74262 points

    Harry,

    Clemens is correct, the value of the pull-down resistor controls the slew rate of the CAN bus signals. If they are too slow for your data rate, this will cause timing issues and is likely what is throwing errors in your system. Using a stronger pull-down resistor (lower value), this will allow the device to work at the highest capable data rate.

    Regards,

    Eric Hackett