• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 34 subscribers
  • Views 313 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.

TCAN1044V-Q1: CAN_H and CAN_L have abnormal output

Amelie Zheng
Genius 10865 points
Part Number: TCAN1044V-Q1


Hi Team,

My customer use TCAN1044VDRQ1 and found CAN_H and CAN_L have abnormal output. Customer already try to change the terminal res and also try to remove terminal res. But have no improvement.

The waveform is as following:

Actually customer use NXP 1042  before and the waveform is normal...

Any advice?

  • 0
    TI__Guru 53575 points

    Hi Amelie,

    Thanks for sharing this issue and the waveforms. 

    It looks like the dominant to recessive (D>R) transition in the TCAN1044 scope shot is very slow. This transition occurs when the transceiver releases the bus and CANH and CANL naturally decay to a common recessive voltage. This means that this transition is relatively independent from the transceiver itself (is not actively driven). The D>R transition time is primarily a result of the RC relationship between CANH and CANL. This includes the bus capacitance of each signal line and the resistance (termination) between them. Generally when I see slow fall times like this, it is caused by either an unterminated CAN bus or one that has a very large amount of bus capacitance or differential capacitance. 

    • In this test, are there any other components on the CAN bus? Bus caps, differential caps, termination resistance, other transceivers? Please include values or a schematic if possible. 
    • Are there any board differences between the two test results shown other than the transceiver swap?

    If there are no differences identified here, we can look further into the difference presented on the CAN bus.

    • Can the resistance between CANH and CANL be measured with a multimeter to ensure that termination is properly in place?
    • Can the capacitance of the can bus be measured (CANH to GND, CANL to GND, CANH to CANL)? Make sure no termination resistance is measured during this measurement.

    Let me know if you find anything else or have other questions in the meantime. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Genius 10865 points

    Hi Eric,

    The terminal res is 1.6k.

    The circuit of TJA1042 and TCAN1044 are the same. Should customer remove the 56pF cap?

  • 0 in reply to Amelie Zheng
    TI__Guru 53575 points

    Hi Amelie,

    Has the customer been able to confirm this resistance with a multimeter measurement? Can they confirm that the capacitance measurements of the two boards is roughly equivalent? 

    Do these abnormal waveforms appear for all TCAN1044 devices tested? Or is this only a few devices that show this behavior? 

    Additional testing with the 56pF capacitor would be fine. I don't suspect that this relatively small value would have such a large impact. I expect the cause has more to do with the resistance between the CAN lines. 

    Regards,
    Eric Schott