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TCAN4550-Q1: TCAN4550-Q1 basic questions

Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4550

Dear team,

My customer has some questions when using TCAN4550-Q1 as below,

1. when pin3 GPIO1 is not used, this pin can be floating,right?

2. does our device support wake up in standby mode? (using CLKIN from MCU schematic) How do I configure related pins?

3. Is this pin related to the wake-up function? If this pin is floating, does this device still have the wake up function?

Could you please help answer these questions?

Thanks & Best Regards,

Sherry

  • Hi Sherry,

    1. GPIO1 is configured by default as an output, so if you leave this pin floating, you will not interfere with the operation of the device.  However, you will not be able to take advantage of the Watchdog input trigger that the pin offers.  If that is okay with you, then you can leave it floating.

    2. The TCAN4550-Q1 does support wake-up in standby mode.  The wake mechanisms are independent of the GPIO1 functionality.  The two wake mechanisms are Local Wake-Up (LWU) through the WAKE pin, and Wake-Up Pattern (WUP) through the CAN bus.  When the device receives a valid wake request in standby mode, the RXD pin and the nWKRQ pin will fall to indicate the wake request to the MCU.

    3. The GPIO1 pin is not related to wake-up functionality.  You may leave it floating and still operated wake-up.

    Please let me know if I can clarify anything further.

    Best Regards,

    Max Megee

    TI Transceiver Applications

  • Hi Max,

    Sorry, the third question I didn't describe clearly. Actually I want to ask :

    Is INH pin related to the wake-up function? If this pin is floating, does this device still have the wake up function?

    Thanks & Best Regards,

    Sherry

  • Ah, thank you for the clarification.

    The INH pin is related to wake-up function.  The INH pin is meant to function as a high-voltage logic output that will act as an enable pin to a system-level power regulator.  When the TCAN4550 device transitions to Sleep Mode, then the INH pin will go low and the system-level power regulator using it will disable in order to save node current during Sleep Mode.  When a wake request is received, then the INH pin will rise again, and the system-level power regulator will re-enable.  

    If you do not wish to use the INH pin for this system-level enable function, then you may elect to float the pin.  There will be no adverse effect on the TCAN4550 or its own wake-up procedure.

    Best Regards,

    Max

  • Hi Max,

    I have another two questions,

    1. If I use a single-ended clock input from the MCU at the OSC pin. Is there any special requirements about the clock type? Is it ok to use PWM square wave?

    2. How to use the wake pin? If I use the wake pin, do I have to configure the circuit as below. What's the function of the resistor 3k ohm, the resistor 33k ohm and capacitor 10nF? And there is a switch connected with ground. Is there any special requirements about the switch? How should I choose the switch?

    Can I connect the wake pin to the MCU's GPIO directly without any resistors, capacitor or switch?

    Thanks & Best Regards,

    Sherry

  • Hi Sherry,

    1. Yes, you may use a PWM square wave from the MCU for the CLKIN signal.  Please refer to section 9.1.1 of the TCAN4550-Q1 datasheet for more information about clock accuracy and speed requirements.

    2. You may not connect the WAKE pin to the MCU GPIO.  The WAKE pin is designated as "high voltage logic input."  This means that the WAKE pin is meant to operate from ground to the VSUP voltage (typically 14V).  So connecting the pin to the MCU GPIO logic output will damage the GPIO.  

    The purpose of the external resistor and capacitor circuit is to protect the TCAN4550 from unwanted Wake events during a DPI event (direct power injection).  The resistors and capacitor act as a filter to keep the WAKE pin stable if noise is injected onto the VSUP line.  The switch to ground may be a simple push-button switch or a logic operated FET.  The purpose of the switch is to provide the toggle on the WAKE pin during Sleep or Standby mode to signal a Local Wake Up (LWU) to the TCAN4550.  After a wake request is registered by a toggle on the WAKE pin, then the TCAN4550 will process the wake request as defined in the datasheet, transitioning to Standby mode, setting the INH pin high, and signaling the MCU via the nWKRQ pin.

    If you do not wish to use the WAKE pin for Local Wake Up requests, then you may connect the WAKE pin directly to VSUP and remove the external circuitry.

    Best Regards,

    Max

  • Hi Max,

    Thanks for your detailed explanation.

    If I want to use the wake pin, I have to connect this pin with resistors, capacitor and switch as below, right? The 33k is to limit the current, right?

    Thanks & Best Regards,

    Sherry