SN74LV123A Q is not changed with simulation

Hi Na Na ,

Yes , I definitely feel that this behavior is strange and I wouldn't know why the model would not have output for the 5s duration pulse. I will bring this up to our modeling team .

Hi ShreyasRao

Thank you for your help.

I'm sorry to trouble you but I would appreciate if you could reply.

BestRegards

Hi Nana ,

I am in touch with our simulation team and will feedback once they have any inputs.
I am certain that the actual device doesn't have this behavior , however will have to look into the simulation model .

Hi ShreyasRao

Thank you for reply.

We want to know if this simulation model is correct or not.
We need to confirm if we keep using this simulation model for evaluation.

We are evaluating this device so we would like to use simulation model before actual device.

Is this problem due to the simulation model?
If so, could you give us a correct simulation model?

BestRegards

Na na ,

thanks for the reminders and I am in touch with the modeling support team and they are scheduled to start later this week.
He had a question :
The model has some parameters that need to be entered by the user.

They appear in the .PARAMS statement in the in model’s netlist:
.SUBCKT SN74LV123A Q Qnot Anot B CLRnot Rext_Cext Cext VCC GND PARAMS: C_EXT=0.001u R_EXT=1000

Those values need to be changed to same values used in the schematic.
If you don’t do this the model won’t give the correct pulse duration.

have you ensured this is right ?

Na Na,

Apologies for delayed response to your question.

It turned out the SN74LV123A model had a bug that caused an error for a particular range of external capacitor values > 50nF.

That has been corrected in the attached circuit. Please give it a try and let me know any feedback you have.

Thank you for your patience.

Regards,
JohnSN74LV123A.TSC

Na na,

I forgot to mention that the model's parameters R_EXT and C_EXT should be set to the same values as the external resistor and capacitor.

This was done in the uploaded schematic.

You can chnage this by double-clicking on those fields on the schematic symbol.

Please let me know if you have any questions.

Regards,

John

Hi John ,

thanks for getting the model corrected. will the updated model be on the web for download as well?

Shreyas,
Yes. The updated model will be posted to the product folder.
John

thanks John ! will be helpful in having for all to have error free models !!

     Hi ShreyasRao,

     Hi Na Na,

     I have a problem similar with Na Na. I built a circuit in Tina with SN4LV123A monostable multivibrator. At the output I expect 50 ms pulse duration. I used Rext=50k and Cext=1 uF and according to this formula Tw=K*R*C (K=1) Tw=50 ms. But at the output I obtain approximately 62 ms pulse duration. You can see my design below.

   According to transient analysis simulation:

    Could you help me how I can obtain 50 ms output pulse duration?

    Best Regards

Would you please post your TINA circuit to this thread?
Regards,
John

   Hi,

   I attached my circuit in Tina.

3566.18.10 Schematic.TSC

Apologies for the delayed reply.

I have confirmed the SN74LV123A model consistently gives pulse durations longer than is specified In the data sheet.

Testing the pulse duration over six orders of magnitude shows that for longer pulse durations, the model's pulse length is 10% to 20% longer than the what is calculated in equation 1 of the data sheet..

For shorter pulse durations, it can be 30% to 40% longer than the calculated value.

We will revise the model to agree more closely with the data sheet.
We will post a message to this thread when the new model is available.

Regards,
John