• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 4 answers
  • Subscribers 23 subscribers
  • Views 637 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN74AVC16T245: The input and output pull up resistor

Lacey Lin
Intellectual 2900 points
Part Number: SN74AVC16T245

Hi team,

I don't see any description about the pull up resistor about the A port and B port.

1. So dose it mean we don't recommend to use the pull up resistor or we forbidden to use the pull up resistor?

2. If customer use the pull up resistor to pull up the A port to Vcca, what will be the issue?

Lacey

Thank a lot!

 

  • 0
    TI__Guru* 97046 points
    Hi Lacey,
    Today is a US Holiday. We will get back with you later this week.
  • 0
    Guru 317170 points
    Depending on the DIR and OE signals, the I/O ports behave like normal CMOS inputs or outputs (or are hi-Z). So using pull-up/-down resistors is perfectly fine. (This would be different with a "H" device with bus-hold circuits.)

    You can always pull up a pin to its own VCC.
  • 0 in reply to Clemens Ladisch
    TI__Intellectual 2900 points

    Hi Ladish,

    Thanks so much for your quick response.

    So my understanding is that if we don't add the pull up resistor, it will not affect the function of the device.

    If we add the pull up resistor, it's better for the device.

    So another question, if we only add pull up resistor in just port A or port B, will this cause issue?

    Lacey

    Thanks a lot!

  • 0 in reply to Lacey Lin
    Guru 317170 points
    Whether pull-up resistors are better, or necessary, depends on your circuit.
  • 0 in reply to Clemens Ladisch
    TI__Intellectual 2900 points

    Hi Clemens,

    Can you help to explain more?

    I can't find any description for the pull up resistor in datasheet.

    So I want to know in which case, it's must to add the pull up resistor, and in which case, the pull up resistor is not necessary.

    Lacey

    Thanks a lot!

  • 0 in reply to Lacey Lin
    Guru 317170 points
    When an I/O pin is an input, it needs a pull-up if no other device is driving a valid voltage level.

    When an I/O pin is an output, it does not need a pull-up.

    When an I/O pin is hi-Z, it needs a pull-up if it is connected to some other device that expects a valid voltage at its input.
  • 0 in reply to Clemens Ladisch
    TI__Guru 62200 points
    Thank you, Clemens for your inputs on this.

    Hi Lacey,
    Would you please let us know more about the application or usage of this device? Generally, strong pullup resistors are not recommended to be used with the pushpull devices like these. There are different class of autobidirectional translators which internally have pullup resistors (TXS) or need them externally (LSF) to be used with open drain devices.
    As Clemens mentioned, a weak pulldown / pullup resistors would be required to be used when the line goes Hi-Z to maintain a valid logic level.