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SN65HVD24: About SUPER-485

Tsukui Yusuke
Guru 21930 points
Part Number: SN65HVD24

Hi,

The following contents are described in the SN65HVD24 data sheet.


My customer wants to implement the above circuit using SN65HVD24.
Could you tell me the recommended SN65HVD24 circuit that supports SUPER-485?
And Please tell me the input/output signal condition, cable condition and speed condition that can realize SN65HVD24.
Customer designed the circuit with a prototype board, but there is a problem that the amplitude of the output signal becomes small.
In the background, we need recommended circuit information that can realize SUPER-485.

Best regards,
Yusuke

  • 0
    TI__Mastermind 25705 points

    Yusuke,

    What's the data rate and communication distance? To clarify, the super485 feature with wide common mode range supports wide ground potential shift, which might not equal to the long distance communication. You can find the detailed discussion about the ground potential difference in section 11 on page 6 this app note.

    https://www.ti.com/lit/an/slla272c/slla272c.pdf

    If the bus signal's amplitude is small, it's commonly due to the cable loss. You can refer to the application space plot on the same page of the datasheet. SN65HVD24 doesn't need any special circuit to make it work. The internal equalization works with small high speed signal.  

    Regards,

    Hao 

  • 0 in reply to Hao L
    Guru 21930 points

    Hi Hao,

    Thank you for your support.
    >What's the data rate and communication distance?
    Data rate is 2～2.5Mbps.
    Communication distance is 0.5m.
    cable is HFA-20
    HFA-20.pdf

    >SN65HVD24 doesn't need any special circuit to make it work. The internal equalization works with small high speed signal.
    I want to show the customer a circuit that can realize super485 by SN65HVD24.
    Could you please tell me the design of circuit example and cable example using SN65HVD24 tested by TI?

    Best regards,
    Yusuke



  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 25705 points

    Yusuke,

    The data rate and distance look benign to me. Could you get more detail about the customer's issue, like setup, waveforms? The datasheet of SN65HVD24 includes many good discussion about the application. A test example is shown in Figure 31, which is 5Mbps communication over 500m Belden 3105A twisted cable. You can compare the results with a regular RS-485 with the same setup.

    Regards,

    Hao

  • 0 in reply to Hao L
    Guru 21930 points

    Hi Hao,

    Thank you for your response.

    I want you to check the customer test circuit.
    Let me send you a private message.

    Best regards,
    Yusuke