openloop transfer function of LDO for load changes

[ahmadiit]

open loop transfer function

Is it Openloop transfer function of LDO due to changes in load current is same as normal tranfer function of ldo i,e Vo(s)/Vi(s).

 

[FvM]

open loop transfer function

No, it's another transfer function Vo/Io or in other words, an output impedance. Any of these input/output transfer functions is closed loop, of course.

 

[ahmadiit]

ldo open loop

can i do stability analysis of Vo(s)/Io(s) , to determine the stability of LDO like Phase Margin of transfer function Vo(s)/Io(s), should be greater than 45 deg for stability of LDO like that.

 

[FvM]

transfer function vo

Zo(s) allone doesn't determine stability, you have to consider the connected load impedance. You can analyze the total output node impedance (parallel circuit of LDO and load) to check stabilty, but the stability criterion would be different to my opinion.