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SN75HVD10: half duplex

Takashi Yamaguchi
Genius 13420 points
Part Number: SN75HVD10
Other Parts Discussed in Thread: SN65HVD10

Hi team,

Can the SN75HVD10 be electrically connected to a device that requires RS-422 (half-duplex)?

Regards,

Yamaguchi

  • 0
    TI__Guru 74292 points

    Yamaguchi-san,

    Technically yes it can because the bus signals can be interpreted by the RS-422, but care will have to be taken of the system design. Will SN65HVD10 act as a receiver to an RS422 commander node? How exactly will this system be implemented?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    TI__Genius 13420 points

    Hi Eric-san,

    Thank you for your support. I couldn't get the feedback about your question from the customer, but could you please help with the additinal questions below?

    1. Can this device (VCC=3.3V) drive a photocoupler by connecting the differential outputs A and B to the anode and cathode of the photocoupler (current limiting resistor 100Ω)? 

    It is stated that VOD (differential output voltage) = 1.5 (MIN). If this is the output voltage, I think it is impossible to drive the photocoupler.

    2. Regarding Figure 17 (HIGH-LEVEL OUTPUT CURRENT vs DRIVER HIGH-LEVEL OUTPUT VOLTAGE) in the data sheet, the voltage rises as the current increases, so is it appropriate as a graph to check the above output voltage?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    Guru 317280 points

    The differential output voltage is specfied for a normally terminated bus. A photocoupler usually needs less current than that. What current do you actually need, and what is the LED's forward voltage at that current?

    Not all information in figure 6 is useful. With an output current of 0, the output voltage is 3.3 V. When the output sources current (which is negative because it flows out of the device), the output voltage drops.