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SN65HVD230: CAN bus ringing

CHEN YAN
Intellectual 1430 points
Part Number: SN65HVD230
Other Parts Discussed in Thread: SN65HVD251, SN65HVD233, TCAN330

Hi, expert

My customer is using four CAN transceivers, and when the receiver node receives right signal, then output ACK. But every node will have a response difference at maximum 250ns. So the CAN bus will see a ring, is this ring matters? can customer reduce this ring by configurating DSP ?

The yellow waveform is DSP CAN1's transmit pin, the red waveform is DSP CAN2's transmit pin, and the yellow waveform is CAN bus's waveform. 

there is a ring in the CAN bus.

Best Regards.

Chen

  • 0
    TI__Guru 62910 points

    Hello Chen,

    As you said, this is most likely because of different response times of each node, which is usually due to differences in propagation delays between each node.  (Some farther nodes would receive the frame slightly later and therefore send an "ACK" slightly later, for example.)

    In general this isn't an issue.  CAN controllers are typically configured to sample the bit value sometime in the second half of the bit period in order to allow some time for the signal to settle after receiving responses from "later" nodes.  So, this sort of ringing would only become an issue if it continued for much longer and resulted in an incorrect bit value.  Please let me know if this isn't clear.

    Regards,
    Max

  • 0 in reply to Max Robertson
    TI__Intellectual 1430 points

    Hi, Max

     Thanks very much for your reply, it's clear, could you please also help on below further questions? 

    （1）The recommended voltage supply of SN65HVD230  is 3-3.6V ，but the maximum VS is 6V，could it be possible to use 5V as VS, if not, what parameters could it influence the performance?

    （2）What's application of 3.3V and 5V can transceivers SN65HVD230 and SN65HVD251, is the higher VS means higher robust while higher power consumption?

    （3）Refer to the parameter common mode voltage of SN65HVD230，CANH与CANL，is it proper to use TVS tube PESD1CAN？

    Best Regards.

    Chen

  • 0 in reply to CHEN YAN
    TI__Guru 62910 points

    Hi Chen,

    I don't recommend operating SN65HVD230.  It was only characterized to operate up to the recommended maximum VCC of 3.6 V and device reliability may degrade if operated beyond the recommended ranges for extended periods.

    Higher supply voltages (e.g., 5 V rather than 3.3 V) wouldn't necessarily be more robust. Both types of transceivers are designed to meet the differential signal requirements (e.g., TX output amplitude, RX input sensitivity) of the CAN standard.  Concerns like RF emissions or immunity to RF/transients would be more a function of the individual transceiver implementations rather than a direct function of supply voltage used.  In general, 3.3-V transceivers can bring a benefit to applications that would otherwise need to generate a 5-V supply to support a CAN interface.  The trade-off with this benefit is that some of the ISO 11898-2 standard requirements may not be met.  (Notably, the CANH output voltage is scaled down.  This does not directly restrict communication since CAN uses differential signaling.  But it would prevent the interface from fully complying to all standard requirements, which may be important for some applications.)

    The lower absolute maximum ranges on CANH/CANL of SN65HVD230 can make it difficult to protect via typical TVS diodes like PESD1CAN.  If this is a concern in your application, you may want to considered a higher-voltage-tolerance 3.3-V transceiver like SN65HVD233.  Or, you could consider a 3.3-V transceiver with a higher level of internal ESD protection (so that it could be used without an external diode) like TCAN330.

    Regards,
    Max