Question about PMOS and feedback circuit for LDO

[mitgrace]

The question of the LDO

Dear All :

I work on LDO design , the chip is come back , We use external PMOS .
and we use feedback circuit to control the LDO , this is very populart structure , But now the Circuit have some problems , the OPen loop of OP is correct , But when we connect the closed loop , The OP's behavior is wrong , I find the PMOS gate has some leakage current , DO I need current buffer after the OP ? I use the PMOS is NDS356 . Does anyone know the PMOS or other part number PMOS , Thanks

 

[alphi]

Re: The question of the LDO

I think such LDO is classic and basic circuit,can you upload you schematic in here,then we can give advanced suggest.

 

[Humungus]

Re: The question of the LDO

What do you mean by extrange? Does it oscillate? Does it settle to a wrong voltage? Does it saturate to one of the rails?

Explain please