LDO Design Related issue

[rshu]

can anybody tell me why we are not using Miller cap for compensation in pmos pass transistor type ldo with full on chip capacitor ?
we are using nmos type ota there as error amplifier.


thanks,
Rohit

 

[dick_freebird]

"We"?

Miller comp on the pass transistor works with a high-Z
(OTA) gate drive there. But it tends to ruin HF PSRR.
Compensating the core amplifier ought to be better
for that, but the huge swing in total loop gain (from
no- to full load) remains a compensation challenge.
If you don't take the Miller gain somewhere then the
comp cap becomes huge.

 

[rshu]

"We"?

Miller comp on the pass transistor works with a high-Z
(OTA) gate drive there. But it tends to ruin HF PSRR.
Compensating the core amplifier ought to be better
for that, but the huge swing in total loop gain (from
no- to full load) remains a compensation challenge.
If you don't take the Miller gain somewhere then the
comp cap becomes huge.

Thanks @dick_freebird for the answer but can you explain me little bit more about how it impacts psrr or refer me any document(paper).

we means our team.