Normal Trench                                                                                                                                                                         

In this structure the channel becomes vertical and needs less horizontal surface than in a planar structure.                        

We can thus further increase the cell density.Also, it removes the JFET structure thus further reducing the Rds(on).          
                 

 Shield Gate Trench             

A kind of amelioration of trench structure: the presence of a shield oxide can help create an oxide charge balance region.   

 The drift region can be strongly doped and thus reduce the on-resistance of the device.                             

CSP

Li-ion battery protection is mainly used for the charge and discharge control IC for overcharge and overdischarge, and the MOSFET will be turned off when the battery is abnormal.

The CSP package Rds comes from Rtotal = Rch + Repi + Rsub, this path is the main resistance,Great influence from Back side metal and metal thickness.