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SN65HVD230: Part corrupts CAN line signals

Part Number: SN65HVD230

Attached below is the schematic of how we used it. The SN65HVD230D corrupts CAN line signals, it works again after replacing it with a new one. Multiple of our boards are experiencing the same problem. 

^Here's a screenshot of what it looks like after connecting the CAN transceiver. The peaks measure around 1.7 and the troughs measure around -2V

^This is the normal CAN signal. Peak/trough: 2.6/1.5V

 

Here are some voltage and resistance values on our functional and non-functional boards.

We are not sure what is causing this problem. 

Thanks!

  • Alvin,

    Based on the resistance and voltage readings of the CAN bus, and the waveforms shared, it looks like some damage has occurred on the CAN bus pins. Based on the CANH to GND voltage it looks like a short is occurring, but the CANH to GND resistance measurement shows a normal reading. Is it possible that some kind of voltage transient or ESD event could have happened during assembly, testing, or handling?

    Also, does this happen after a length of time during some kind of testing? Or is this right after assembly?

    Regards,

    Eric Hackett 

  • Hi Eric,

    I'm also working with Alvin on this issue.

    This is happening after standard use. It works initially but after some time it fails and we haven't been able to pinpoint what happened before it breaks down. There are other devices that are still working on the CAN bus line (eg. the BMS from our battery) so we're confused why only this transceiver is failing.

    We have a PESD2CAN ESD protection on CANH/L up to 30 kV but that's the only protection we have on the transceiver (other than the bypass cap on Vcc). The datasheet (https://www.ti.com/lit/ds/symlink/sn65hvd230.pdf) on page 34 shows bus filter capacitors that seem like they might be useful. What values do you recommend for that?

    Any advice will be very helpful.

    Thanks for your support!

  • Adonis,

    Thanks for the reply, this is a strange one. Given that this is happening under typical conditions, and you have enough protection on the bus lines for transient protection, it doesn't seem like an ESD or random transient event is happening. From your oscilloscope screenshots of the fault device, it also looks like the CANH and CANL signals are being internally shorted.

    Once you have removed the problem device, have you placed it on another board to see if the problem persists? I assume it would, but I just want to make sure we look at everything. In terms of bus filter capacitor values, they can range from 10pF to 150pF typically, and the value will depend on how many nodes are on the bus. The more added capacitance, the bigger the loop delay for each bit, so the more nodes you have, the less bus filter capacitance you can have. I'd recommend 50pF to start out.

    Regards,

    Eric Hackett 

  • Hi Eric,

    Sorry for the delay - it's been a bit busy for me and thanks for getting back.

    We removed the CAN transceiver from our board but it broke in the process unfortunately, so we threw on a brand new transceiver our board started working again - was able to read/write onto the bus.

    We will put the bus filter capacitor on to see if that helps it out and also try to pinpoint what happened right before it broke since we might be missing some part of a bigger picture.

    Thanks for your support!

    Best,

    Adonis

  • Adonis,

    Good to hear that the issue went away with a new part. If anything gives an issue, please don't hesitate to post your question here again.

    Regards,

    Eric Hackett