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Original question:

TCAN4550-Q1: About the External crystal oscillator: When applying CAN communication, i must use external crystal oscillator...

TCAN4550-Q1:

Gabriel de Sousa
Prodigy 10 points
Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4550

Tool/software:

Hello team,

I have a question, in my application we use the Bus Wake via RXD_INT Request (BWRR) in Sleep Mode to detect CAN activity and wake up the host MCU using the nINT pin (CANINT). 

The clock is sourced from the MCU using a pll, but when the core is in stop mode (after setting the TCAN4550 to sleep mode) the MCU stops clocking the TCAN4550.

Is the TCAN4550 still able to detect CAN activity and wake up the host MCU when the clock is off? 

  • +1
    TI__Mastermind 33030 points

    Hi Gabriel,

    The nINT pin will not be operational until a clock is provided because this is controlled by the digital core.  So it is not useful to wake up the MCU if the clock is also controlled by the MCU.

    Instead the INH and nWKRQ pins are used to provided pin to indicate a wake event.  The INH pin is considered a High Voltage pin and will be driven to the VSUP voltage when the device wakes up to Standby mode.  This is generally the preferred pin if it is connected to the EN pin of a power regulator.

    The nWKRQ pin is a low voltage pin and powered by an internal 3.6V rail that is on during Sleep Mode.  It can be configured to be open-drain and require an external pullup resistor to VIO if VIO will be on while the MCU is asleep.  When the device wakes up into Standby mode, the nWKRQ pin will be pulled Low, similar to how the nINT pin will be pulled low, and this can be used as an interrupt to the MCU.

    By default the nWKRQ pin mirrors the INH function, but with a polarity inversion along with different voltage levels.  But it can be configured to act as a wake request interrupt pin.  While this second option sounds like what you want, it does require the clock to be active so that the digital core can set the interrupt bit in the register stack which is required prior the nWKRQ pin reflecting this bit.  So, if you would need to use the nWKRQ pin in the default "mirrors INH function" in order for it to be active while the MCU is asleep and there is no clock and or VIO supply voltage active.

    Hypothetically speaking if you were able to keep the VIO supply and Clock active during Sleep Mode, the nINT pin would be pulled low after the TCAN4550 has woken up into Standby mode, which would in turn allow it to be used an interrupt to the MCU. But because you do not have clock, the nINT pin will not be active until after the clock becomes active and stable.

    Regards,

    Jonathan

  • +1 in reply to Jonathan Nerger
    Prodigy 10 points

    Thanks for clarifying.