fanrong
Banned
Added after 22 minutes:
This is a LDO's driver and current limiter .
The refernce , pmos pass device , feedback resistor network are not shown here.
Vss is input voltage , Vss=6V
Vb1,Vb2 is the bias voltage , make the current of unit W/L current source and sink
0.5uA .
Vo is the LDO's output , Vo=5V
Vref is the refence , Vref=1.2V
Vfb is the feedback , Vfb=1.2
shut is the shut signal , Vshut = 6V
The W/L :
M1 : 32/3 , M2: 8/80 , M3 : 64/8, M4 : 32/8
M5 : 64/8 , M6 : 32/8 , M7 : 8/3 M8 : 8/80
M9 : 16/16 , M10 : 16/16 M11 : 16/16
The driver and current limiter should limit the current :
When Vo > 0.8 , and not in low drop out region , Imax=400mA
when Vo<0.8 , Imax=200mA
When low drop out , no current limit .
My question is :
As u can see, when Vo< 0.8V , M1 ,M 3 are shut off .The current source M 9, M 12 can't balance the curent of M 5, M7,M12 when vo <0.8 . So the voltage of
A is very low . So how the driver and current limiter limit the current under 200mA
when Vo < 0.8V .