aaron_do
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Hi subgold,
I think i've found out why it was oscillating (managed to get it to stop), and i'll see if i can post it after I analyze it to make sure. As for the analysis, I broke the loop with an iprobe and ran an stb analysis.
I realize with three gain stages I should have three poles and therefore a poor phase margin, but I guess due to the sizing of the stages, the PM didn't need compensation.
You mentioned that the CMFB should be able to regulate the circuit even when the operating points are deviated from the desired values. I was wondering about that too since I usually only ensure good PM at the operating point (my circuits input and output CM are fixed). However, on start-up, the PM is probably very different from what it is at the desired operating point. So how do we normally deal with this?
thanks, Aaron
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