Hi,
I tried to simulate a circuit using SN74LV123A in orcad. The pspice model was downloaded from TI site.
I am using two multivibrator models in a circuit.
The first multivibrator consist of:
A high to low pulse given at ANOT, B and CLR is HIGH.
According to our design, Rext = 200k and Cext = 100nF. But when I give these values and simulate, I am always getting a low value at Q (approx 52uV).
I am only getting a pulse at Q when Rext is given 200 MEG and Cext is given 10nF. And, with this combination of Rext and Cext, the width of the pulse should be 200MEG*10nF = 2s. Unfortunately, I am only getting a pulse width of 32ms. Why is it so? Why I am not getting the correct logic of Rext and Cext? Is there any limitation in the model for Rext and Cext values?
Also, I have to use second same multivibrator in the same circuit with :
ANOT and CLR high and B is connected with Q of the first multivibrator
Rext = 100k and Cext = 100nF, and I am taking the output from QNOT.
And the output of QNOT should be high to low. But, I am sometimes getting a constant high voltage and sometimes getting a low to high pulse.
Why is it so?
Regards,
Sreelekshmi.
