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SN74LV123A: the minimum input retriggering time

n ninomiya
Prodigy 10 points
Part Number: SN74LV123A

Tool/software:

Hi,

I have any questions.

I have a question about the minimum input retriggering time.

Looking at the input and output relationship in Figure 7, I understand that if t_rr of /A is shorter than t_w, output Q will remain High, and if t_rr is longer than t_w, output Q will alternate between High and Low.

I am considering this in conjunction with the Rext/Cext waveforms.

However, it says that t_mir=t_w*0.3 is the minimum input retrigger time, but where does this fall in relation to Figure 7?

Best Regards,

Ninomiya

  • 0
    Guru 317370 points

    In figure 7, if trr is less than tw × 0.3, then the retrigger might not happen, and the pulse width is only tw.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Thank you for your reply.

    I have two questions.

    1.

    If Ct is 0.066uF, is K=1?

    It says that if Ct is >1000pF, K=1, but in Figure 3, the vertical axis is in mF, so 0.066uF=0.000066mF, and K=2.3.

    Which is correct?

    2.

    I experimented with a circuit where t_w=0.017[s].I calculated t_w as K=1.

    I thought the retrigger threshold was t_mir=t_w*0.3, but when the input t_rr is longer than t_w=0.017[s], the output Q alternates between high and low (i.e. a retrigger occurs). Is this correct?

    I'm using it as a rising edge detector, and the waveform is as follows:

  • +1 in reply to n ninomiya
    Guru 317370 points

    1. The axis label in figure 3 is using the wrong font; the unit should be µF.

    2. The datasheet guarantees that retriggering happens after tmir. It does not make any guarantees for intervals shorter than tmir; retriggering might or might not happen.