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TCAN4550: Wake pin question

Mihir Gupta65
Intellectual 2155 points
Part Number: TCAN4550

Hi Team,

Is it possible to awaken an MCU from sleep mode via WUP (Wake Up Event) on the CAN bus and is the response indicated by the TCAN4550: "nINT" pin?, i.e. communicated to the MCU? Or do you absolutely need the "nWKRQ" line to wake up an MCU?

As I understand it, a WUP should be displayed on nINT and switch the controller from sleep mode to standby mode, but it is not clear from the documentation.

Thanks and Regards,

Mihir

  • 0
    TI__Mastermind 26270 points

    Hi Mihir,

    Yes it is possible to awaken an MCU from sleep mode via a WUP (Wake Up Event) on the can bus.  There are a couple of different methods to do this, but using the nINT pin is probably not the preferred method since the MCU would need to be in a state that could monitor the state of this pin.  I would think that sleep mode would not allow the MCU to monitor this pin, but once the TCAN4550 detects a WUP, it will pull the nINT pin low to indicate the TCAN4550 has changed from sleep mode to standby mode.

    Generally, the INH pin is used for waking up the MCU following a WUP.  The TCAN4550 will drive the INH pin to the VSUP voltage in all modes except for Sleep Mode where the INH pin is placed in a Hi-Z mode.  When the TCAN4550 detects a WUP on the CAN bus, it will wake up and change states to Standby Mode which will then drive the INH pin high.  Typically the INH pin is connected to the Enable Pin of a power supply device such as a LDO or DC-DC regulator that supplies the power to the MCU.  Once the INH pin goes high, the enable pin of the power supply is enabled and produces power which will cause the MCU to power-on and enter its default initialization routine.  This is the most common method for waking up the MCU from sleep.

    The TCAN4550 has an internal 5V LDO that also becomes active when the device is not in sleep mode.  Therefor it too will become active following a WUP and if you use this LDO for the MCU supply, or connect it to the enable pin of a larger power supply, it too will cause power to be restored to the MCU causing it to wake up.  If your power supply enable is not tolerant of the VSUP voltage, the VCCOUT 5V may be a better lower voltage option.

    Then nWKRQ and nINT pins will also reflect the wake up event and can be monitored for state changes by the MCU or other circuitry.  However in order to use these pins as an indicator, the MCU or monitoring circuit must have enough power to be able to monitor the voltage on these pins and then wake up the MCU.  Typically, the MCU is completely powered off or put to sleep to conserve the maximum amount of power and only the smallest amount of circuitry inside the TCAN4550 that is supplied directly from the higher voltage VSUP rail will remain active and monitor the CAN bus for a WUP.  This in turn will control the rest of the board's power supply and wake up the entire board when a WUP is detected.

    You can reference the Typical Application Figures in the TCAN4550 datasheet to see how the INH pin can be connected to the EN pin of a voltage regulator and how it powers the external MCU.

    I hope this clearly answers your question but please let me know if anything is still unclear or you have any additional questions.

    Regards,

    Jonathan