what's the function of this type of LDO ckt?

[youda.chen886]

i dont understand the purpose of this special LDO
i just know there's a pmos used to sense current ....
anybody could tell me more?

 

[erikl]

See this response!

 

[youda.chen886]

It is over-current protection?
but why does the sensed current need to be added to the reference voltage?

 

[erikl]

It is over-current protection?

Yes!

why does the sensed current need to be added to the reference voltage?

I would compare its voltage to a reference voltage (with some hysteresis) to completely switch down the output voltage.

In order to achieve a fold-back current limiting -- which might be more favorable in terms of thermal power management and application simplification -- one would subtract the current sensor's created voltage over R_s from V_ref (as indicated in the image by "or -") -- or add it to V_fb .