• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 20 subscribers
  • Views 920 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.

SN74LV123A-Q1: How to terminate unused channel

Ron Michallick
Guru**** 164956 points
Part Number: SN74LV123A-Q1

I need a 229ms high output pulse when a low input edge is received.

Please check my selection for R , C for the used channel.

How do I terminate unused channel? Can I leave Cext, Rext/Cext pins open?

qq.pdf

  • 0
    TI__Guru**** 164956 points
    Where do I add the protection diode to protect device from VCC fast power down (or VCC short to GND).
    The data sheet mentions current on pin 2 and 14. Pin 2 makes no sense.
  • 0
    TI__Guru* 97046 points
    Hey Ron,
    The Cext pin is internally grounded - if you want, you can also externally ground it, but it's not required. The Rext/Cext pin is fed directly into a comparator and nFET to ground (discharge path for external capacitor), and should be tied to ground. You could instead tie this line to Vcc, but if the channel were to somehow trigger, the device would attempt to discharge Cext, probably damaging the device.

    I would recommend reducing your resistor choice to something closer to 100 kohm (or less) and increasing the capacitor accordingly. The Rext/Cext input can have up to 2.5uA of leakage, and that would produce a sizable voltage across the 2.5Mohm resistor. I have operated our monostable multivibrator devices with very large capacitors (up to 100uF) without seeing any adverse effects.

    Please let me know if I can be of further assistance.