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I'd like to know some details about the BUF802 auxiliary path and its effects on the feedback loop of the op amp. In the datasheet there are several drawings of the circuit connecting the AUX_IN pin to the main path. In the first screenshot, IN_AUX is abstractly controlling a current source, and in the second there is some more detail showing AUX_IN connected to an emitter follower, with some unspecified internal biasing resistors Ra and Rb visible.
From what I gather, the purpose of this circuit is to better isolate the low-frequency op amp path from the high-frequency main path, compared to a conventional composite loop where the LF and HF paths are combined with a simple resistor-capacitor network. Without the RHF+CHF pole directly in the output path, the op amp phase margin and closed loop bandwidth are improved and the crossover frequency shifts higher.
But in lieu of this simple connection, what has replaced it? My goal is simulate the op amp feedback loop as connected to the BUF802 in CL mode, finding the closed loop bandwidth and phase margin. The datasheet gives one clue to use, that the auxiliary path gain (G_AUX) is 0.2. So is it sufficient for this goal to put some ideal gain block of 0.2 between the op amp output and the beta network in my simulations? Or is there a better model I should use?
Hi James,
Is the goal to run a stability analysis and replace the BUF802 aux path with an ideal gain block for your simulation?
Best Regards,
Ignacio
Is the goal to run a stability analysis and replace the BUF802 aux path with an ideal gain block for your simulation?
Yes. What is the best model to use for the connection from IN_AUX to OUT in a simulation?
Hi James,
We do have the BUF802 model available with the IN_AUX pin. It would be hard to outright turn that signal path into a simple gain block as there are other affects that could not be captured simplifying the signal path this way.
Best Regards,
Ignacio