SN74LV123A: The guide line for how to choose the parameter for the Tw

Hi Lacey,

K cannot be set - it is a byproduct of nonlinearity in the operation of the monostable multivibrator.  You first select a capacitor, which sets the K value (figure 2 in the datasheet), then it's easy to calculate the resistance required based on the desired pulse width with this equation:

tw = K*R*C

Let me know if I can be of further assistance.

Hi Lacey,
The value doesn't really matter - as long as your calculations are correct. We always recommend prototyping with monostable multivibrators to tune the pulse width to the application.

What matters more than the capacitor value selected is the _type_ of capacitor you choose. Resistors typically don't change that much over temperature and you can get 0.1% accuracy resistors relatively cheap. Capacitors, on the other hand, can vary huge amounts over temperature, and it's not uncommon to see 20% or more for the manufacturing tolerance of the nominal value -- and very accurate and temperature insensitive capacitors can be expensive. I'd recommend contacting a capacitor manufacturer if you want to learn more.

The simple fact is that monostable multivibrators are inherently not all that accurate. If your customer is looking to get an incredibly accurate 1ms pulse, then I would recommend finding a different method (microcontroller + crystal oscillator). However, if they are ok with ~1ms, then a monostable multivibrator is a good choice.