LDO Design Related issue

rshu · Mar 19, 2024

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 · Mar 19, 2024

"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 · Mar 20, 2024

dick_freebird said:
"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.

LDO Design Related issue

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LDO Design Related issue

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