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Original question:

HVDA551-Q1: HVDA551-Q1: Output differential voltage abnormal

HVDA551-Q1: CANH CANL waveform jitter

Beida Song
Intellectual 810 points
Part Number: HVDA551-Q1


Tool/software:

Hi Expert,

Customer find HVDA551-Q1 CANH and CANL waveform jitter and the low level voltage is about 0.7V, which is higher than 0.5V. Every board has this issue, so this could be related to schematic and layout.

The schematic is shown as below. Which parameters does I need to check? For the layout, there is other CAN NET near to this HVDA551. Whether the other CAN affect the waveform quality?

The waveform is as below:, the orange line is the differential signal. The Pink is CANH, the yellow is CANL.

  • 0
    TI__Genius 14632 points

    Hi Beida,

    How is termination implemented on the CAN bus? When the test is ran, how many other CAN devices are on the bus? A diagram here would be helpful.

    The two farthest end nodes should have 120 Ohm termination resistors in place. This will minimize reflections and improve the signal quality:

     

    Another note is that there seems to be a lot of capacitance on the CANH/L lines as can be seen from that schematic drawing. The ESD diodes also add capacitance. I do not believe this is the cause of the noise you are seeing, but the capacitance might be outside the recommended budget. 

    Additionally, I would highly recommend switching to TCAN1044AV-Q1. It has improved bus fault protection, wider supply voltage range, faster data rates, and an overall improved product at a lower price. Due to its improved drive tolerances, it will likely have less noise/jitter as well. 

    Best,

    Ethan