SN74LVC1G123: SN74LVC1G123 minimum retrigger time calculation

Hi,
Do not understand anymore, If we have 100nF, the retrigger should be more than 1us (figure 7 from datasheet)

hi
I found an other E to E comment :
As for the retrigger time, this has to do with the discharge rate of the timing circuit. although it is not precise, I would recommend using 0.1*Rext*Cext for this value to be safe. The largest value I have seen in our data is actually 0.09*Rext*Cext. The multiplier decreases inverse to capacitor size -- ie a 1uF capacitor has a multiplier closer to 0.00003, and a 100pF capacitor is closer to 0.09.

From that I do not understand where this formula coming from?
does this recommendation (0,1 * Rext * Cext) refer to my actual system (121k / 100nF) which is to be used on our board?
Is this recommendation based on any technical documentation ????

did you – by now - get any official answer to my request, concerning
the retrigger time (if used 121k/ 100nF) ?
Can your recommendation (0,1 * R * C – in our case 1,21ms) be officially confirmed (datasheet)?

Kamal,

You are correct - I mistakely read your 100nF as 100pF and gave you the wrong value. The recovery time for 100nF isn't listed on the plot because data was not taken for it. I would estimate it to be ~10us just based on the data available. The best way to verify would be to build your desired circuit and test.

The answer you saw to Satoshi-san was referenced to some experimental data I took, and looking back at it, I can see that it is incorrect. Rext should not affect the recovery time as previously stated, however the equation I gave would give you a safe time for recovery -- 1.21ms is certainly enough time. I believe that 20 us would be sufficient.

Can you tell me more about your application? What makes the recovery time so critical? Perhaps we can improve the application rather than going down a rabbit hole on this part.

hi,

So if I understand carefully, the 100nF for the recovery time would give an estimated time of 10us and there is not way to calculated it.

Can you tell me which equation you gave me ? which is correct.

I only have the equation you mention :  (0,1 * Rext * Cext) which Rext affect the recovery time.

so is this equation correct?

if yes why it is not mention on the datasheet?

Regarding your question, about the application, I will need to ask the customer but before I need answers from you.

REGARDS,

Kamal

 

 hi again,

just to be clear I am only talking about the RETRIGGER time.

what I need from you is to confirm the equation for the retrigger time : (0.1*Rext*Cext)

what is the minimum retrigger time possible?

What is the retrigger time by using 121K and 100nF ?

hi,
Thank you for your clear message.

What remains is the feeling that the datasheet lacks important information. Quite
unusual for TI-devices-datasheets.

I can understand your frustration.  

It is especially difficult in Logic to please everyone with our datasheets since our parts get used in so many varied applications.  In this particular application, a capacitor was chosen outside the values given on the datasheet.  Personally, when I choose external components for an application like this, I try to stick with the ones that the datasheet has already.  If I have to go beyond it, I test them thoroughly myself since the part might have never been designed to work with them.  Fortunately for this case, I have tested this part and found that it is incredibly resilient.  Even with fairly large capacitors (10 uF) it still works perfectly fine.

I wrote an app note on the subject available here: Designing with the SN74LVC1G123 Monostable Multivibrator

Unfortunately, I don't think it will help with this particular application.