• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 33 subscribers
  • Views 576 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN65HVD231: Can powered SN65HVD231 drive VCC of unpowered SN65HVD231?

Nick Denniston
Prodigy 100 points
Part Number: SN65HVD231


I have two separate boards, each with an SN65HVD231 transceiver, that can communicate with each other successfully. In a previous version of the design, both boards were powered from the same external +12V supply and generated their own +3.3V supply.

In a new revision, one board (Board #1) generates its own +12V supply while the other board (Board #2) continues to use the external +12V supply. I connected the CANBus lines between Board #1 and Board #2, and I powered Board #2 from the external +12V supply while leaving Board #1 unpowered. This means that the CAN transceiver on Board #1 was powered, active, and generating messages to an unpowered transceiver on Board #1. The current draw from the +12V supply to Board #2 was about twice as much as normal.

If I powered Board #2 from the external supply without the CAN connection made to Board #1, the current draw was nominal.

I reconnected the CAN lines between Board #1 and Board #2 and powered Board #2 from the external supply; eventually Board #2 failed with a short on the +12V line. This happened on two separate instances of Board #2. I am in the process of troubleshooting the failed boards, but the only connections between the Board #1 and Board #2 are a return connection and the two CANbus lines. Is it possible that the powered CANBus lines back-drove VCC through the CAN transceiver on the unpowered Board #1, attempting to drive the entire +3.3V load on Board #1 and burning out? If so, is there any way to prevent this?

  • 0
    TI__Guru 62920 points
    Hi Nick,

    That's a good thought, but the SN65HVD23x devices were designed to have high impedance CANH/CANL lines when unpowered and have blocking diodes integrated internally to prevent larger bus voltages from back-feeding current into VCC. So, I wouldn't expect that to be the problem here. To help better understand how one board might be affecting one another, though, would it be possible to take a look at the CANH/CANL/VCC pins of the unpowered board on an oscilloscope? Also, you mentioned that the current doubled when the unpowered board was connected - what is the level of current? (I ask because there will be some leakage into CANH/CANL of an unpowered transceiver, but this should only be around a couple hundred uA.)

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points
    I can get scope traces, but I will most likely blow another board doing so. I'm trying to get some replacement ones out of stock that aren't connected to a battery so that they are easier to rework; then I'll get some captures and post them.
    The normal current draw of Board #2 is about 35mA; the current draw increased to ~75mA when running the power through Board #1 (where there should no longer be any load, although the returns are common).
  • 0 in reply to Nick Denniston
    TI__Guru 62920 points

    Nick,

    To avoid damage to the board, perhaps you could try introducing some resistance in the connection between boards in order to limit the current. Then, you could gradually decrease the resistance until the onset of the issue can be observed (hopefully before damaging current levels are reached).

    Max

  • 0 in reply to Miguel Robertson
    TI__Guru 62920 points

    Hi Nick,

    I just wanted to check back in.  Has there been any progress on resolving this?

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    Prodigy 100 points

    Hi Max,

    I received m replacement boards yesterday and hope to test tomorrow.

    -Nick

  • 0 in reply to Nick Denniston
    Prodigy 100 points

    Hi Max,

    I've been unable to reproduce the issues on the new circuit boards, so it seems to be unrelated to pushing +3.3V backwards through the transceivers. Because the original boards were soldered to a battery stack and the replacement boards are not, I'm thinking the problem is due to hot-plugging/unplugging the batteries instead of any kind of low voltage power paths.

    Thanks for the support; I will close this issue.

    -Nick

  • 0 in reply to Nick Denniston
    TI__Guru 62920 points

    Nick,

    Thanks for the update, and I'm glad the issue didn't re-appear.  If you have any follow-up questions please don't hesitate to contact us.  Just wanted to let you know I'll be out of office for the next couple of weeks, though, so if you do have follow-up questions it would be better to start a new thread (so that one of my colleagues is more likely to see it).

    Max