Cant understand what this part of the circuit does

[hrishib]

Hi, Can anyone please help me understand this circuit (see the attached PDF. The part I cant understand is in the red box in the top left corner). Is this some sort of power-path control? This is basically a Li-Ion battery charger. The MOSFET seems to be controlled by the CHRG pin which goes low when charge is complete and otherwise stays high. The high and low on this pin are logic levels. I tried simulating this in LTSpice IV (also attached) but couldnt really understand what it does. This part is actually optional but I'd still like to know what it does. Any help would be appreciated. Thanks!

 

[Harald Kapp]

Read this article with emphasis on the part that describes figure 4.

Basically you have either the MOSFET or the diode, not both. The MOSFEt operates as a controlled diode in this circuit to prevent reverse current.

 

[hrishib]

Thanks Harald!! That certainly helps. Wonder how I missed that document...