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TCAN1043-Q1: TCAN1043 wake up problem

Jimmy Huang22
Expert 1470 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hi Ti team,

        I used TCAN1043 to replace TJA1043,used nfault pin to wake up MCU.

1, Do you help us check that can use nfault pin to wave up MCU in standby mode?

2, I used nfault  pin to wave up MCU find below problem

When MCU sends NSTB low voltage, CAN in standby mode . CANH/L has no information, nfault will cause an error low votalge  to wave up MCU, find this problem not in every time.

  • This phenomenon has occurred in several machines

  • Test condition:Vbat=6V, at room temperature

    • The test waveform and sch is as follows:

    • 3,

      • Could you please help us confirm the possible cause? the NXP TJA1043 no find this problem with nfault pin to wave up mcu.


  • 0
    TI__Guru 62920 points
    Hi Jimmy,

    This could happen if the WAKE line toggles. A change of state on WAKE will result in a NFAULT going low while the device is in standby mode, and this low level does not clear immediately when entering normal mode. (If the wake-up request came from the CAN bus, NFAULT would clear immediately. This feature allows the user to distinguish the source of the wake-up request.) Four recessive-to-dominant edges on the TXD line should clear the fault indication.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Expert 1470 points

    Max,

       Does Wake line toggles been the  Tcan1043  Wake pin? 

    CH1:nfault

    CH2:nSTB

    CH3/4: CANH/L

  • 0 in reply to Jimmy Huang22
    TI__Guru 62920 points
    Jimmy,

    Yes, if the WAKE pin toggles then it causes the TCAN1043 to exit sleep mode. This will cause the NFAULT output to assert low until the CAN bus toggles a few times in normal mode. Please let me know if this isn't clear.

    If you didn't intend to toggle the WAKE line, you may want to try observing it on the oscilloscope when this issue is occurring. There may be some noise coupling onto this pin that is causing an unintended wake-up.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Expert 1470 points

    Max,

    Thanks for your reply,then I test the Wake pin, no find some noise on it when in sleep mode.test picture as below.

    Whether there are other possibilities can cause nfault to low voltage to wake up mcu when in sleep mode. 

    thanks!

  • 0 in reply to Jimmy Huang22
    Expert 1470 points
    Max,

    Add one question, Is there a requirement for ripple with Vsup pin? datasheet no find this spec. thanks!
  • 0 in reply to Jimmy Huang22
    Expert 1470 points

    Max，

    Add a message，The RX pin has been drop out at the same time,as below

  • 0 in reply to Jimmy Huang22
    TI__Guru 62920 points
    Jimmy,

    Both NFAULT and RXD will go low in standby mode when a wake-up request is received. The RXD line will go high when the part transitions to normal mode (as long as the CAN bus is recessive). The NFAULT line will go high along with it if the wake-up request came from the CAN bus. If it came from the WAKE pin, though, then NFAULT will stay low until TXD toggles.

    In your image, the WAKE line looks to be at about 3.5 V. This is between its high-level and low-level input thresholds. Can you please pull it either to GND or VSUP so that it is at a defined logic state (high or low - either one is OK)?

    Does this behavior only occur at VSUP = 6 V?

    Does NFAULT de-assert after the TXD line toggles? (I would expect four falling edges to clear NFAULT.)

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Expert 1470 points
    Max,

    Thanks for your advise.

    I used a 100K resistor to connect wake pin with Vsup,then no find this problem

    Please help to confirm whether it is ok to pull up the wake pin from 100K resistor to Vsup, and what is a better recommendation? Vsup voltage from 6V to 36V

    If whether it is ok to pull down the wake pin from a resistor to GND,and what is a better recommendation.
  • 0 in reply to Miguel Robertson
    Expert 1470 points

    Max,

    Thanks for your advise

    Pls help us confirm whether it is ok to pull up 100K resistor from wake pin to Vsup,and what is the recommendation? Vsup voltage from 6V to 36V

    Whether it is ok to pull down a resistor from wake pin to GND,and what is the recommendation?

  • 0 in reply to Jimmy Huang22
    TI__Guru 62920 points
    Hi Jimmy,

    I'm happy to hear that this is resolved! It is OK to tie WAKE to either VSUP or GND. Typically I recommend tying it to VSUP since this results in slightly lower supply currents in sleep mode. You may want to use a smaller resistance value like 1 kOhm to provide a stronger bias and help reduce susceptibility to noise.

    Max