TINA/Spice/THS4521: convergence problems and unexpected results in simulations using the new model released in 2016-Dec-18

Tool/software: TINA-TI or Spice Models

Hello,

I am using the THS4521 to drive the ADC ADS1278. I need a gain of 5 in order to cover the complete range of the ADC. In the datasheets there is the following example with gain 1.

ths4521.pdf

I am trying to simulate the same circuit but replacing the feedback resistor with 5k. From now I will call the feedback resistor RF.

1. Using the PSpice model (release date: 2016-Dec-18, downloaded from ti.com) to simulate with Cadence (Allegro), the simulation with RF=1k looks fine, but with RF=4k it does not converge.

   3276.PAGE1.pdf

   Using RF=3k, I get the following result:

   1. bias.pdf

      1. It looks like VOUTM is clipping, but it is not even close to the rail. The common mode, the output and the input voltages are all within the operation ranges, and I still get this unexpected result. Could you confirm if this is a problem of the model, or if there is some other phenomenon I am not understanding?

2. Using the TINA model from the library that comes with the software, all the simulations seem to work as expected. But the Macro for that model was released on 2009. If I download the latest model released in 2016 from ti.com, the results look similar to my Allegro simulations. I also tried downloading examples published in this forum by TI employees, and replaced the THS4521 model by the newer Macro, and some of them won't converge.

I am attaching my TINA and Allegro files.

Thank you a lot for your help.

2009_THS4521_driver_circuit_for_ADC_ADS1278.TSC

2016_THS4521_driver_circuit_for_ADC_ADS1278.TSC

ti_adc_driver_sim.zip