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AD8561 Latch function not working in simulation.  I'm simulating a circuit using the AD8561 and not able to get the latch function to work. I set up a simple test circuit with 5V pwr and GND (a single supply circuit). I put a reference voltage on one input and a pulse source on the other.  The Q and NQ outputs work and change as expected.  When I add a pulse source to the Latch input, the outputs never latch.  In my simulation I wait 1ms after the inputs change to assert the latch but the output does not latch. Set up a pulse source (0-5V) that is "held" on the Latch input.  I'm using Microcap that can read PSpice files.  (All the other AD spice models I have used work fine in this simulator). I looked at the AD subcircuit model syntax for the latch and switch sections and they look okay. No errors from the simulator. May try in LTsice to see if I get a different result.  Any suggestions?

  • Hi,

    Thanks for pointing out. I agree that the latch function is somewhat off in the model.

    If you want to see the functionality of the model with latch function, I'm attaching a sample test circuit wherein I added behavioral voltages at the output Q and Qnot.

    Unfortunately, as of now, I'm not aware of a function to retain the last value of voltage which is how a latch function works.

    It might need to be done using another implementation in spice or LTspice in particular but the consequence of it is that you might not be able to run it in other simulators because components in the model will be proprietary to LTspice.

    The attached sample latch implementation needs considerable changing of time delay values in behavioral sources added depending on the latch pulse timing. Also, the transient analysis is altered by start saving data at a particular time in order to show the effect of latch is translated in the output correctly (not a perfect solution for now)

    Here is a sample result.

  • Thank You,

    Based on your answer I'll do some testing on the the actual part to characterize the latch function. I can probably add some extra components or a behavioral block to the output of the AD8561 component to make it latch.