• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 19 subscribers
  • Views 428 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.

SN74AVC4T774: value of pullup resistor for dir

WONHO KIM
Prodigy 120 points
Part Number: SN74AVC4T774

i could not find the valuen of pull up resistors  for dir control in datasheet.

  • 0
    Guru 316670 points

    CMOS inputs are high impedance; any value between 0 Ω and 1 MΩ will work fine. What value to use depends only on the requirements of the rest of your circuit.

  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    Thank you, Clemens

    I can see same sentece as you said. 

    but how to calculate the resistance to ensure the current-sinking capability of the driver?

    is there any mathematical method before release PCB or experimental way after fabrication?

    The output-enable OE input circuit is designed so that it is supplied by VCCA and when the OE input is high, all outputs are placed in the high-impedance state. To ensure the high-impedance state of the outputs during power-up or power-down, the OE input pin must be tied to VCCA through a pullup resistor and must not be enabled until VCCA and VCCB are fully ramped and stable. The minimum value of the pullup resistor to VCCA is determined by the current-sinking capability of the driver

  • 0 in reply to WONHO KIM
    Guru 316670 points

    The DIR input is not the OE input.

    Do you actually need to have high-impedance state of the outputs during power-up or power-down? If not, you can connect OE directly to GND.

    The minimum value of the pullup resistor is interesting only if you need to switch very fast. This is usually not the case for the OE pin, so you can use a high value that saves power, such as 10 kΩ. Also see [FAQ] How do I size pull-up or pull-down resistors?