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SN65HVD234: Receiver Input Resistor Matching

Daniel Minors85
Prodigy 140 points
Part Number: SN65HVD234

1. There is no figure given in the datasheet for receiver input resistor matching.

2. There is no figure given in the datasheet for Driver symmetry.

Can those values be provided?

  • 0
    TI__Guru 74282 points
    Daniel,

    The receiver input resistance is provided on page 8, and a simplified illustration of the receiver input internal circuit is shown in figure 28 on page 18. Can you elaborate a bit on what values you would like relating to driver symmetry?

    Regards,
  • 0 in reply to Eric Hackett
    Prodigy 140 points

    Hi Eric,

    The standard ISO11898-2 defines an driver symmetry of 0.9 - 1.1, from the formula vsym = (VCAN_H + VCAN_L)/VCC.  Assuming the datasheet worstcase values for VCAN_H and VCAN_L i work this out as just outside the limits.

    The standard also defines the receiver input resistance matching, the datasheet provides single ended and differential resistance, but i cant equate that to how the two resistors are matched.  The ISO standard requires mR = -0.03 - 0.03, (mR = 2 × (RCAN_H − RCAN_L)/(RCAN_H + RCAN_L).

    I wondered if you have specified values for these parameters.

    Best Regards,


    Dan

  • 0 in reply to Daniel Minors85
    TI__Guru 74282 points
    Daniel,

    It's important to note that while 3.3V CAN transceivers are compatible with ISO11898-2, they are not compliant with it. One of the reasons for this is because of how 3.3V CAN transceivers are designed to be compatible with 5V transceivers on the bus, and what you pointed out in the driver symmetry formula. Because the 3.3V recessive level is shifted up to 2.0V to work with 5V CAN buses, instead of VCC/2 = 1.5V, the transceiver does not comply with the definition of a 5V CAN transceiver.

    In the datasheet, RIN can equate to RCAN_H and RCAN_L in the ISO specification. The intention of the design of the CAN bus lines would be to make them perfectly symmetrical. The datasheet parameter RIN is meant to imply that CANH and CANL resistance are identical (and fall within the range of the datasheet), and thus satisfy the requirements of ISO11898-2. I will look for characterization data to see if we have the actual values available.

    Regards,