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Original question:

MAX232: About unused pins

MAX232: About unused pins

Shinji Kato
Prodigy 60 points
Part Number: MAX232

Regarding unused pins, the following answer was given.

     No; these logic inputs must not be allowed to float, so you need to connect them to VCC or GND.

7.3.2 of the datasheet states that there is a pull-up resistor.

I hear that there is a pull-up resistor, but is it better not to use it open?

  • 0
    TI__Guru 57880 points

    Hi Shinji,

    I need to verify if the TIN pins have an internal pull up resistor. Since I do not see a functional block diagram of the device with internal pull up resistors in the diagram, I'm a little hesitant to confirm they actually exist. Sometimes datasheet errors are carried over from previous datasheets or have errors that were never caught. 

    If TIN has internal pull up resistors then you can leave them floating. If they do not,  then you must reference the pins to either GND or Vcc. 

    I'm currently checking to see if I can find a design engineer who can confirm TIN has internal pull up resistors, I will get back to you when I find out.

    Sorry for the delay,

    -Bobby

  • +1 in reply to BOBBY
    TI__Guru 57880 points

    Hi Shinji,

    Design engineers got back to me. Looks like we did design internal pull up resistor into a diode to Vcc. So Tin for this device can float since they have internal pull ups. 

    -Bobby