Hello!

I am analyzing stability of a number of circuits using AD8513, my first approach is through PSpice simulation and rate-of-closure criteria. So first, I need to confirm the model of this opamp behaves as it is depicted in its datasheet. In Figure 17 "*Open-Loop Gain and Phase vs. Frequency"*, the X-axis starts at 10kHz and ends up to 50MHz. I ran an AC Sweep simulation to replicate Figure 17 (open loop, RL=2.5k and Cscope=20pF):

From comparing the right hand plot versus the left hand plot, one could assume that the model behaves as it is expected from the datasheet:

The question rises when the X-axis of the same plot above is zoomed out to start at 1Hz in the PSpice simulation; the phase is reversed 180° at low frequencies (lower than ~61Hz). **Is the model of the opamp inaccurate? or I should expect such behavior at low frequencies?**:

Thanks a lot for your support and your time!

Hi,

The spice models are usually modeled based on what you see on the datasheet. In the case of AD8513, the open loop gain and phase vs frequency plot is from 10kHz to 50MHz only in the datasheet. Anything beyond that is likely not modeled Ex. 1Hz to 1KHz, 51MHz above. Based on the simulation results you presented in correlation with the datasheet, 10kHz@ 90 degree phase, unity gain (0dB) @ around 45 to 50 degrees phase margin and 28MHz @0 degree phase are modeled.