Mikay wrote on Feb 6th, 2014, 11:49am:Thanks Rob, there may be a in-band doublet in the band gap loop. The loop was not analyzed in detail manually since it's a very complicated architecture. But to ensure a quick loop response, extensive Monte Carlo simulation has been done and all of the simulation results show the band gap starts up very quickly(less than 300ns). Is it possible Monte Carlo simulation could not predict the doublet space(p1-z1) very accurately and thus the far spaced doublet degrade the speed in the end?
After thinking about it a bit, it would have to be a vary large mismatch or your doublet is at very low frequency to get a time constant in the 400us range. What are you using for the load capacitance? Maybe it has a large ESR (equivalent series resistance), but it seems unlikely to be that large.
Maybe you are getting some feedback via parasitics into your bandgap or opamp that is shutting it down. These can recover slowly if they are biased lightly or have big filter caps on it.