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SN65HVD230: No signal on CAN-H pin

gary speiser
Prodigy 20 points
Part Number: SN65HVD230

Vcc and Ground are OK

I see data on the D input; 1's and 0's toggling.

Rs Pin is pulled down.

I see good data on the CAN-L line (data is toggling like the D input) but the CAN-H line is stuck high.

Output is terminated with two, 120 ohm resistors; one on each end.

I tried 2 parts - both with the same issue.

Thank you for any help you can give me.

  • 0
    TI__Guru 62920 points
    Hi Gary,

    That sounds strange - I'm not sure what might be going wrong. When you say CANH is stuck high, is it at 3.3 V (equal to the VCC level)? Does the level change at all as CANL toggles? What voltage range do you see on the CANL pin - is it close to 0 V for dominant periods and close to the CANH signal level during recessive periods? Have you tried any other CAN transceivers on this PCB and had success? Any potential for a short-circuit or soldering issue?

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 20 points
    Thanks Max.
    After investigating things a bit more, the CAN-H line does have a small noisy signal around 2v amplitude. I can tell that it's an inverse of the CAN-L signal but really ugly. Feels like a bad part but I tried two boards with exactly the same result. I ordered some individual CAN Transceiver parts and I intend to solder them on to the two boards (which came with the transceivers onboard) as soon as they arrive.
  • 0 in reply to gary speiser
    TI__Guru 62920 points
    Hi Gary,

    Trying another device/resoldering sounds like a good strategy. If you haven't already, you may also want to use a multimeter to verify that the CANH pin properly connects to the bus and to the termination resistances and that there are no short-circuits from CANH to other nets (like VCC). Please let us know if problems still persist. If you'd like us to look over your schematic/PCB layout as well, we would be happy to do so.

    Max