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TCAN4550-Q1: time sequence requirements in MCU side for wake up process

Daniel Wang (auto)
Intellectual 1770 points
Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4550

Tool/software:

Hello team,

Kindly ask two questions about time sequence:

Background: The MCU needs to be woken up with a TCAN4550, customer need to check which time point need to be set by MCU side.

Question: 

1. Can the following CLKIN/Crystal time points be changed, and are there any requirements?
2. What are the requirements for the time points that need to be supported by the MCU during the wake-up process?

Thanks!

  • 0
    TI__Mastermind 25330 points

    Hi Daniel,

    Daniel Wang (auto) said:
    1. Can the following CLKIN/Crystal time points be changed, and are there any requirements?

    The Crystal/CLKIN circuit is powered by the VIO supply pin which is commonly disabled during sleep mode because this is usually the power supply for the MCU as well. If the VIO supply has been disabled during sleep mode, it will need to be enabled (usually through the INH pin connected to the regulator's enable pin) so that the crystal can start oscillating. 

    The startup time of the crystal will depend on the the inductance of the crystal and the load capacitance.  This can vary between different types of crystals and board layouts.

    Once both VSUP and VIO supplies are on and the crystal is oscillating, the TCAN4550's digital core will be functional and transition into Standby Mode and indicate this by pulling down the nINT pin.

    Therefore, the timing will be dependent on how long the VIO voltage takes to ramp and the crystal to start oscillating.  Both of these are outside the control of the TCAN4550.

    Daniel Wang (auto) said:
    2. What are the requirements for the time points that need to be supported by the MCU during the wake-up process?

    I don't understand, typically the TCAN4550 is waking up the MCU.  You have not indicated by what method the MCU is going to wake up, so I can only speak generally.

    Typically the INH pin of the TCAN4550 is connected to the EN pin of the low voltage regulator that supplies the MCU.  During Sleep mode, this low voltage regulator is disabled causing the MCU to power down.  The VSUP is always connected to the TCAN4550 and only a small internal circuit is powered to monitor for a wake up, either through a Wake Up Pattern (WUP) on the CAN bus, or a Local Wake Up (LWU) transition on the WAKE pin. 

    Once a Wake Event has been detected, the TCAN4550 will wake itself up and drive the INH pin high which enables the low voltage regulator that supplies the VIO voltage to both the TCAN4550 and the MCU.  The crystal on the TCAN4550 then starts to oscillate and the MCU starts it's power-on boot process.  Once the MCU has booted, it can re-initialize the TCAN4550 registers and start it's application.

    If however, the application does not use this traditional process, then the MCU will need to verify the TCAN4550 has entered standby mode (either through monitoring the nINT pin, or through SPI register polling) prior to initializing the TCAN4550 registers.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    TI__Intellectual 1770 points

    Hello Jonathan,

    Thanks a lot for your detailed feedback.

    Our further question is, it may take long time to power and give clock to TCAN4550, i.e. 100ms after MCU was waked up by nWKRQ, is it okay for TCAN4550 to work correctly? Is there any other timing constraint for MCU to give power/clock/other control signal to TCAN4550?

    Thank you.

  • 0 in reply to Daniel Wang (auto)
    TI__Mastermind 25330 points

    Hello Daniel,

    There is only one timing requirement that is part of the failsafe features called the Sleep Wake Error (SWE) Timer which is 4 minutes in length.  When the TCAN4550 wakes up, this timer starts and the Power ON (PWRON) flag needs to be cleared through SPI, or the device needs to be placed into Normal Mode through SPI.  Therefore, you have 4 minutes for the Wake Up and provide the clock and configure the TCAN4550 before it will transition back into Sleep Mode.

    Compared to the 4-minute SWE Timer, 100ms is nothing.  See the Failsafe Feature section of the datasheet for more information.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    TI__Intellectual 1770 points

    Hello Jonathan,

    Thanks for your support. Customers have another question about Standby Mode WAKEx function:

    From below diagram, it showed that WAKEx(static mode) is working in standby mode. If WAKEx assert, besides relative register will record this wakeup event, what else action will happen? i.e. nINT assert?

    Thanks!

  • 0 in reply to Daniel Wang (auto)
    TI__Mastermind 25330 points

    Hello Daniel,

    The Local Wake-up event can cause the nINT pin to assert if it is enabled in the Interrupt Enables register (0x0830).  If the LWU bit is set to "0", the nINT pin will not assert.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    TI__Intellectual 1770 points

    Hello Jonathan,

    Thanks for your support.

    Is it correct that If WAKE_CONFIG is configured as edge triggering(whatever rising edge, failing edge or Bi-directional edge), CONFIG WAKE_WIDTH_INVALID and WAKE_WIDTH_MAX will be ignored by SBC?

    Thanks!

     

  • 0 in reply to Daniel Wang (auto)
    TI__Mastermind 25330 points

    Hello Daniel,

    Yes, those parameters are only associated with the Pulse Wake Configuration.  If the device is configured for an Edge configuration, it will see any edge transition corresponding to the configuration (rising, falling, or either) as a valid wake event and respond immediately. 

    Regards,

    Jonathan