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SN65HVD232Q About definition of Vod in datasheet

Tomoaki Yoshida
Expert 2200 points

Hi,

I have a question about definition of Vod in datasheet.

There are two descriptions of the VOD(D) upper of the data sheet on page 7.

What difference is the upper and lower ?

Although it has been terminated with 60Ω, the minimum value of the termination resistor is 85Ω in ISO11898.

Are these data  not related to ISO11898?

How was it defined the resistance of 167Ω in figure 2?

Although I think this device is conformed to the ISO11898, I can't understand whether this data is associated ISO11898.

I would like to understand the meaning of these data.

Best regards,

Tomoaki Yoshida

  • 0
    TI__Guru 62920 points
    Hello Yoshida-san,

    The difference in the two specs is the presence of common-mode loading/biasing. This is not included in the upper spec (referenced to Figure 1), but is included in the lower spec (referenced to Figure 2).

    CAN applications typically use a 120-Ohm termination resistance at each end of the bus. These two resistors in parallel present an equivalent differential load of 60 Ohms to a CAN driver (120 Ohm || 120 Ohms). That is why 60 Ohms is used in the test circuit.

    The 167-Ohm resistance are included in Figure 2 to emulate the effects of a fully-loaded CAN bus. In this case, each transceiver on the bus will present some additional loading to the active driver. The resistors connect to a test voltage that represents the reference (ground) potential of the passive transceivers. This is varied over some range in order to represent ground potential differences that can occur across a bus. These ground potential differences give rise to common-mode differences between the different transceiver.

    Please let me know if this is still unclear.

    Regards,
    Max