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TCAN1043-Q1: CANH & CANL high logic value without 120ohm resistor

Marvn Arcangel
Genius 13650 points
Part Number: TCAN1043-Q1


Hi Expert,

Customer's system lose 120ohm resistor, and they test the CANH high logic is only 866mV regard to GND. And high level logic of CANHL to GND is also 866mV. Besides, Vsup =12V, VCC=EN=5V, Vio=3.3V.

Is it normal?

image (10).png

Thanks and regards,

Marvin

  • 0
    TI__Guru 54596 points

    Hi Marvin,

    No, figure 8-2 shows a typical bus voltage range. Normal recessive where CANH = CANL is around 2.5 V or VCC / 2. 

    Removing termination changes the bus impedance but should not as low as 1 V and suspect both lines are being pulled toward GND externally or a failure mode.

    • You may isolate the bus by disconnecting all other nodes to confirm
    • Ensure the power supplies are reaching their thresholds and not sagging
    • Capture CANH and CANL single ended and the differential to compare with the data sheet's VO and VOD specs to further clarify, thanks.

    Best Regards,

    Michael.