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TINA/Spice/CD74HC221: Requesting TINA SPICE models or equivalents for possibly obsolete parts

Part Number: CD74HC221
Other Parts Discussed in Thread: TINA-TI, CD4035B

Tool/software: TINA-TI or Spice Models

Hi, Team,

I am requesting information on TINA SPICE models for the following parts (or suggestions for possible equivalents):

74HC221 - (The only multivibrator I can find in TINA is a 74121)


Analog Devices AD7819 - (8-bit Parallel Out, Single Channel SAR ADC)

I am attempting to replicate a simulation from an old schematic from the 1980's, for educational purposes.

Thank you very much.

James Suttles

  • Hi James,
    We do not currently have an available PSpice model for any CMOS monostable multivibrators (like the HC221). We recommend prototyping rather than simulation with this type of device. This is due to the nonlinearity factor (K) that is a function of the connected capacitor value. PSpice just plain out doesn't support modifying a model based on a passive connected to it. We have been working on a possible work around for a while, but it's unlikely that it would be available this year.

    We have a similar trouble with shift registers like CD4035B. It's extremely intensive for PSpice to model the internals of a shift register since it wasn't designed to support digital circuits. Ideally we would make a model that has analog inputs, a digital core, and analog output. Unfortunately, this is just something that we haven't been able to accomplish yet. Again, we are working towards a fix, but we probably won't see results in the near future.

    I don't support SAR ADC's for TI -- if you have a question regarding PSpice models for those, I would recommend creating a new post and using the appropriate TI part number to find the right team to answer.

    Please let me know if I can be of further assistance.
  • Mr. Maier,

    Thank you very much for your quick reply. I am aware of some of the problems that SPICE simulators
    have had with digital circuits. But, I did not know of the larger issues involved. Thank you again for
    your help. James Suttles