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SN74LV13A tw value

user4775773
Intellectual 300 points
Other Parts Discussed in Thread: SN74LV123A

      Hi,

      I designed a circuit in Tina by using SN74LV123A monostable multivibrator. In this design I expect 50ms tw at the output pins(Q) of SN74LV123A. According to tw=K*R*C formula I used 5k resistor and 10u capacitor to obtain 50ms tw at the output. But I obtain approximately 62 ms at the output and this value is not useful for my design. I used below formula to calculate tw value. Could you help me how I can obtain 50 ms tw? I attached my circuit.

     Regards,

Schematic.TSC

  • 0
    TI__Guru 62350 points
    Hi ,
    I for some reason cannot open the tina circuit attached .
    adjusting the R and C based on the observed tw is suggested.
    Going by fig14 , I would suggest using 1uF cap and using higher values resistor to set the tw. To be a precise at 50ms, accurate RC are recommended . with 20% cap and 1% R , the tw could reach 60ms and variation of temp and applied bias voltage across a ceramic cap can vary the C values a lot .
  • 0 in reply to ShreyasRao
    Intellectual 300 points

         Hi,

          I added circuit again.I adjusted capacitor value as 1uF and then I changed resistor values. For example if I want to obtain 110ms I used R=110k and C=1 uF but I obtain approximately 140ms.I couldn't understand this sentence ''To be a precise at 50ms, accurate RC are recommended . with 20% cap and 1% R'' .Could you explain this sentence with an example?

        Regards,

    4338.15.10.TSC

  • 0 in reply to user4775773
    Intellectual 300 points

        Hi,

        I adjusted tolerance values of capacitor and resistor as C=%20(C=1uF) and R=%1(R=50k) to obtain 50 ms output pulse.But I obtain approximately 55 ms at the output and it is not useful for me.How I can obtain 50 ms at the output?

       Regards, 

  • 0 in reply to user4775773
    TI__Guru 62350 points
    what I meant was the R and C will have its tolerance range within which it can vary and will affect the pulse width.

    assuming K=1 , the RC time can vary between 60.6ms(1.2uFohm x 50.5kohm) to 39.6ms(0.8uF x 49.5kohm) .
    55ms is within this range.
    you will require a 1% cap and 0.1% R to get close to the desired values.(49.45 - 50.55ms)