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SN65HVD256: Application issues

Reed
Expert 1280 points
Part Number: SN65HVD256

Hi,

CAN signal waveform abnormality.

Schematic diagram:

-----------

Test points: SN65HVD256DR-6P
Test GND: SN65HVD256DR-8P
Test conditions:
DC high voltage: 320V
DC low voltage: 18V
Compressor operation

Note: There is also common mode interference on the CANH (SN65HVD256DR-7P) waveform

-------------

Test conditions:
DC high voltage: 0
VDC low voltage:18V
Compressor shutdown

Green: CANH
Yellow: CANL
Purple ：CANH-CANL

------------

Test conditions:
DC high voltage: 320V
VDC low voltage:18V
Compressor is working

Green: CANH
Yellow: CANL
Purple ：CANH-CANL

-----------

Test conditions:
DC high voltage: 320V
VDC low voltage:18V
Compressor is working

VCC 5V and 3V

-----------

  • 0
    TI__Guru 55050 points

    Hi Reed,

    I've assigned one of our CAN experts to this thread, they should get back to you by tomorrow.

    -Bobby

  • 0
    TI__Mastermind 24925 points

    Hi Reed,

    CAN transceivers do not cause ground shift like this. This waveform shape is very likely caused by your compressor's interference with the cabling. CAN receivers are able to reject this common-mode noise and focus exclusively on the differential signal, as shown in the purple line CANH-CANL. As long as these signals remain within the recommended operating conditions, the device should behave normally.

    I'd recommend reevaluating your cabling layout to see if you can provide some additional clearance between your compressor and the cable harness. Also, consider some sort of shielding if you're trying to eliminate this noise pattern.

    Best,

    Danny