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TCAN4551-Q1: RGYRQ1

Huajian Li
Prodigy 70 points
Part Number: TCAN4551-Q1

Tool/software:

Dear everyone：

Recently when we recently used the chip TCAN4551, we found that the waveform was low in the middle and high on both sides. Because this part is not a terminal node, so when this component was tested separately, a 60ohm resistor was connected in parallel at the end of the cable. The terminal resistance is removed, and the wiring diagram for the test is as follows.

  • 0
    Prodigy 70 points

    So what is the reason for the appearance of such a low middle height waveform on both sides?

  • 0
    Prodigy 70 points

    Correction, the terminal resistance on the schematic was removed, but during the test, the 60 ohm resistance at the end of the cable was connected

  • 0 in reply to Huajian Li
    TI__Mastermind 33430 points

    Hello Huajian,

    The smooth varying wave-like amplitude change seen in the waveform are typically the result of impedance changes and reflected energy traveling along the bus.  The impedance is the product of the ratio of inductance and capacitance for both the wires as well as the components such as the common mode choke, discrete capacitors and resistors, PCB traces, etc. 

    As the signals travel along the bus and encounters a change in the impedance, some of the energy is reflected that can then interact with the source signal and alter the amplitude.  CAN buses typically have termination at both ends of the bus, to dampen reflected energy at both ends from returning back to the source.

    Regards,

    Jonathan