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SN65HVD234: CAN TX signal blocked

Luca Giambonini
Prodigy 10 points
Part Number: SN65HVD234

Dear TI,
in our PCBA design we use the component SN65HVD234D with a STM32F103 controller to send and receive data in our CAN bus line.
This PCBA is used on field in an elevator installation. The SN65HVD234D is used in many nodes in our CAN bus system in the elevator and we never had any issue, except for this very specific installation where we experience a weird effect. This installation suffers of bad power supply and noises on the main line.
For any reason it seems that the transceiver stop sending CAN messages but it continue to receive them. The STM32 send the messages, but using a CAN analyzer does not shows nothing on the line. To make it working again a power cycle on the PCBA must be performed.
Looking at your datasheet is written:
> Designed for operation in especially harsh environments, the devices feature cross-wire protection, overvoltage protection up > to ±36 V, loss of ground protection, overtemperature (thermal shutdown) protection, and common-mode transient protection > of ±100 V

If any of this condition occurs, what is the behavior of the SN65HVD234D? the device autorecover?
Is possible that only the TX line is being blocked caused by an external interference?

Transceiver connection:

CAN input filter/protection circuit:

  • 0
    TI__Guru 65812 points

    Luca,

    The behavior of the transceiver receiving data but not transmitting is how the device behaves when it is in silent mode. Silent mode is controlled by the Rs pin seeing at least 0.75*VCC, which in a nominal case would be 2.475V.

    Is it possible to share oscilloscope screenshots of the Rs, VCC, CANH, and CANL pins when the device starts showing this behavior?

    Regards,

    Eric Hackett  

  • 0 in reply to Eric Hackett
    Prodigy 10 points

    Dear Eric,

    thank you for the information, but is unlikely that the RS pin will float to  0.75*VCC. We discovered instead that the circuit was introduced an additional 120ohm termination. That can be the source of the problem and we are testing it.

    Unfortunately is not possible to give you the oscilloscope analyze, is on the field and this kind of measure can't be done.

  • 0 in reply to Luca Giambonini
    TI__Guru 65812 points

    Luca,

    Yes, I agree it is unlikely. Adding another 120 ohm termination will reduce the overall bus impedance to 40 ohms, which would heavily attenuate the CAN bus signals. This would make it so the dominant threshold for the receiver isn't ever crossed, leaving the bus recessive indefinitely.

    Regards,

    Eric Hackett