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TCAN1043-Q1: Initial INH Pulse on Power Up

Casey McCrea
Guru** 103215 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

Hey Team,

I'm working with TCAN1043-Q1 and trying to figure out this behavior which I noticed regarding the wake/INH circuit. I am using the TCAN1043-Q1 EVM with no modifications except to short the WAKE pin to GND with a jumper. I've noticed that on initial ramp of the VSUP voltage, the INH pin goes high for about 200ms even though the WAKE pin is held low. This only happens once on initial power up for VSUP, but I'm wondering if there is a way to prevent this from happening. Other than that, the WAKE circuit works as expected. 

See scope shot:

Purple = VSUP

Green = Wake

Yellow = INH

Best Regards,
Casey 

  • 0
    TI__Intellectual 2090 points

    Hi Casey,

    Thank you for your inquiry. 

    Normally we expect the INH pin to rise to around VSUP-1V during power up and stay high during the operation of the TCAN1043, with the exception that INH will go high-Z and decay to 0V when the device enters sleep mode.  The WAKE pin should have no effect upon the INH pin outside of sleep mode.  When the WAKE pin toggles in sleep mode, then the INH pin should respond by transitioning from 0V to VSUP-1V (low-to-high).  It is certainly curious that you see INH staying high for only 200ms upon power up and then going low, but there should be no functional dependency on the WAKE pin in this case. 

    I am curious what your power up sequence looks like.  Are you using a VIO voltage supply?  The TCAN1043 possesses an under voltage timeout feature for the VIO supply (specified between 160ms and 340ms) that will place the device in sleep mode if VIO remains low for too long.  In this case, the INH pin will fall after the VIO under voltage counter times out.  

    Otherwise, are you placing the device into sleep mode via EN=High and nSTB=Low?  This also might explain the falling edge on INH, since INH is expected to be low in sleep mode.

    Let me know your feedback on the two items above (VIO supply state and Control Logic Pins).  See the State Diagram below from the datasheet to follow the paths I have highlighted above:

    Power up -> Standby -> Under Voltage VIO Timeout -> Sleep Mode

    Power up -> Standby -> Go-to-Sleep Mode -> Sleep Mode

    Best Regards,

    Max Megee

  • 0 in reply to Max Megee
    TI__Guru** 103215 points
    Hey Max,

    I'm actually trying to start the device directly into sleep mode so I'm supplying only VSUP and keeping VIO/VCC grounded. Since VCC and VIO have not been applied, I have done nothing with EN or NSTB.

    Best Regards,
    Casey
  • 0 in reply to Casey McCrea
    TI__Intellectual 2090 points

    Casey,

    In that case, what you are seeing is expected behavior from the device.  As I said above, the TCAN1043 powers up into Standby Mode, and INH will rise.  Since VIO and VCC are never supplied, the device will timeout to Sleep Mode after the t_UV counter expires.  Typically that timer is ~200ms, so what you are seeing is expected behavior.

    Is there anything else I can help you with?

    Thanks,
    Max

  • 0 in reply to Max Megee
    TI__Guru** 103215 points
    Hey Max,

    That makes sense. I was hoping there was a way to power the device directly into sleep mode or to suppress the initial INH pulse because in my system I have the VCC and VIO supplies enabled by the INH signal. That way when the CAN WAKE signal is detected the VCC and VIO will power up and the device will go into standby mode (and stay there). Unfortunately because of the initial INH pulse, when the power is first powered, the INH pulse triggers the downstream regulators to come on and forces the board into standby mode automatically. From there I have to go back and toggle nSTB in order to get the board back into sleep mode. Do you know if there is a common scheme that is used to prevent this behavior?

    Thanks,
    Casey
  • 0 in reply to Casey McCrea
    TI__Intellectual 2090 points
    Casey,

    Do you have a particular application that requires this? I don't know of any clean way of suppressing the INH pin during Standby Mode; moreover, from a reliability point of view, I would tend to advise against that route, just in case INH somehow is suppressed when you actually want it to power up and enable the external regulators. Keep in mind that you would be operating the device outside of its recommended functionality. I would hate to land in a "perpetual sleep mode" somehow if the INH pin gets suppressed and VCC/VIO under voltage timers keep you returning to sleep mode.

    Regards,
    Max
  • 0 in reply to Max Megee
    TI__Guru** 103215 points
    Never mind about it. If you would like to know more about the application we can take it into email, but apparently this is not a request you have seen before.