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TCAN4550-Q1:Single-Ended Clock Input

takatsuki0204
Prodigy 10 points
Part Number: TCAN4550-Q1

Hello.
Regarding the single-ended clock in TCAN4550-Q1, when a single-ended clock is input to OSC1, how long should OSC2 be left GND (low) to switch to a single-ended clock input?
Also, how is the CAN output data affected if it is misidentified as a single-ended clock while operating with an external clock?
Is part of the CAN data missing as if it were fixed to HI or LOW, or is no CAN data generated and output?...

Is the waveform output from OSC1 temporarily disturbed at the timing of switching from external clock to single-ended clock input?

  • +1
    TI__Mastermind 33020 points

    Hello takatsuki0204,

    The OSC2 pin must stay connected to GND for the device to remain in single-ended clock mode.  If the voltage on the OSC2 pin rises above the detection threshold that is typically 100mV, but could be between 90mV and 150mV, it will switch to the crystal oscillator mode.

    If the clock mode is misidentified, the device will not have a working clock to operate the digital core or CAN controllers.  If this happens, the SPI and CAN communication will fail because they require a clock to operate.

    When the device switches from the crystal oscillator mode to single-ended mode, the transimpedance amplifier will stop supplying current to the crystal from the OSC1 pin and instead expect a single-ended clock to be provided on this pin.  If a crystal is attached, the voltage waveform will still show an oscillation because the crystal and load capacitance form a L/C resonance, but the peak-to-peak amplitude of the oscillation will start to decay because of the resistive losses in the circuit and the amplifier is not supplying a replacement current.  The common mode voltage will also change as a result of a change of impedance in the circuit and the removal of the feedback resistor. However, because the crystal oscillation waveform on the OSC1 pin will not meet the 0V to VIO single-ended voltage requirements, the TCAN4550-Q1 will not have a functional clock to run the digital core and CAN controller.

    Additional information about the clock circuit can be found in the TCAN455x Clock Optimization and Design Guidelines application note.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 10 points

    Is it possible to check if the clock is switched to single-ended clock during the operation? What is the measurement method?

  • 0 in reply to takatsuki0204
    TI__Mastermind 33020 points

    No, there is no status or detection method to indicate which clock mode is being used.  However, if the wrong clock mode is active, the device will not have a functional clock to operate the digital core and CAN controllers and communication will fail.  SPI errors are reported when there is no functional clock during register read/writes.  This is probably most common indication that the clock mode is incorrect.

    Regards,

    Jonathan