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MAX3223E: Unused channel

Hideki Hayashi1
Expert 7350 points
Part Number: MAX3223E
Other Parts Discussed in Thread: TRSF3221E, TRS3221E, MAX3221E

Hi team,

If the use-case is that 2nd channel (DIN2・DOUT2・RIN2・ROUT2) was not used, how can customer to set pins? Open or pull-up to Vcc or pull-down to GND?

Regards,

Hayashi

  • 0
    Guru 276420 points

    Unused outputs can be left open. Unused inputs must not float; the DIN pin requires an external pull-up or pull-down, while the RIN pin has an internal pull-down.

  • 0
    TI__Guru 57930 points

    Hi Hayashi,

    Generally, we recommend input pins be biased to either GND or VCC. Output pins that are unused may remain floating. This means pins like DOUT2 and ROUT2 can be left floating.

    The RS 232 receiver RIN2 is tied to the INVALID logic, where if the voltage sits between -0.3V and +0.3V for longer than 30uS then the device will flip the invalid logic and enable the auto-powerdown. This pin is already tied to GND  by a 5k resistor (see application information diagram on page 12 of datasheet).

    One concern I see is if the Auto-powerdown feature is enabled/used on this device, leaving RIN2 floating (internal 5k to GND would trigger this) could trigger it. If we tried to tie the pin to Vcc and a short to 25V occurred, this could damage the power tree on the Vcc rail. 

    If you don't need the auto-powerdown then leaving RIN2 floating (internal 5k to GND) would be okay.

    DIN2 is an input meant for processors/microcontrollers and can simply be tied to either Vcc or GND with a resistor. 

    Is there a reason why you can't move to a single channel RS232 device? 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 10 points

    Thank you for your answer.
    The above questions were submitted by Mr. Hayashi on my behalf.
    I understand how to handle unused pins.
    I have an additional question.
    I would also like to consider a single channel RS232 device, so could you please provide me with the product number?

  • 0 in reply to Koki Morita
    Guru 276420 points

    The MAX3223E supports 500 kbaud and has auto-powerdown and good ESD protection.

    Similar 1+1 devices are the MAX3221E/TRS3221E (250 kbaud) or TRSF3221E (1000 kbaud).

  • 0 in reply to Koki Morita
    TI__Guru 57930 points

    Hi Koki,

    I agree with Clemen's response for suggested devices. Please let us know if you have further questions.

    -Bobby