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SN75ALS191: Connection of not needed pins

Michael Daimer
Intellectual 1725 points
Part Number: SN75ALS191

Hello,

can you please recommend, how to connect the pins of the second driver, if only one is needed in my circuit? Can you leave all pins floating of the second driver?

Second, the negative output of the first driver is also not needed. Can it be left floating or what is your recommendation for connecting the pin?

Thanks and best regards,

Michael

  • 0
    TI__Mastermind 26806 points

    Michael,

    Thanks for reaching out!

    For unused input pins on any device, I always recommend connecting them to VCC or GND as appropriate for design. When input stages remain floating, it would usually not cause any damage to the device, but it frequently causes significant current consumption, since the input stage would be sitting at midrail, allowing current to pass through the stage from VCC to GND.

    Here, tying the unused input A to a voltage rail would be recommended.

    Unused output pins can be left floating if desired.

    Remember that, for proper operation, the device needs external biasing pursuant to RS-485/RS-422 requirements (see datasheet Figure 1 and Figure 2). I would recommend applying RL between outputs Y and Z, even if you are ignoring one of them.

    Best,

    Danny

  • 0 in reply to Danny Bacic
    TI__Intellectual 1725 points

    Hi Danny,

    thanks for your recommendation. Helped a lot!

    Best regards,

    Michael