hi guys:
As an classical LDO,comprised by three stage:an high gain stage,a buffer stage and a output stage.A big cap is at the output and the esr is essential to the stability.
There are 2 poles and 1 zero in the loop.My question is when the loading is changing and the 2 poles will be changing and the dominant pole will be exchanged between the 2 poles,how to analysis the stability issue?
Can anyone help,thanks~~
In most of LDOs, the dominant pole will change as load. For light load, the dominant pole is at the output node. For heavy load, the dominant pole might locate inside. However, you can design a LDO that dominant pole is at outout node for your max loading if all internal poles are pushed to very high frequency.
Added after 1 minutes:
or internal poles are compensated by internal zeroes. Many commercial LDO has internal zeroes to form pole-zero pairs.