Hi,
In LDO design, the output stage is a big PMOS device acting as a scurrent source. It is always called "passive deivce". Why it is called passive deivice? It is coompared to the active deivce?
This PMOS in LDO can be regarded as a pass transistor of a voltage-controlled current source.
As such, it is like having a load-insensitive (ideally) source resistance (which is a passive element but non-linear). Hence you can also regard this a passive.
i am sorry, i know little about LDO.
could you explain why the PowerMosfet operate in active region?
does the PowerMosfet sometimes operate in saturation region, sometimes operate in linear region??
i am sorry, i know little about LDO.
could you explain why the PowerMosfet operate in active region?
does the PowerMosfet sometimes operate in saturation region, sometimes operate in linear region??
Almost all LDO pass device operate in saturation region instead of linear region. Some recent authurs
published papers operating LDO pass device in linear region to minimize device area. However, for pass device in linear region, it hurts PSRR as linear region will directly couples any noise from gate or input source to the output, almost no PSRR at all.
the minimum voltage to keep the power MOSFET work in the saturation region, because if the power mosfet leave saturation region ,it will not supply constant current to the load