UCC28070: Current Sense Circuit Explaination in UCC28070 Evaluation Module

Hello Sachin, 

The part of the current sense network that you highlighted in red is not absolutely necessary for PFC operation. 
Minimally, the part circled in blue is all that is necessary. 

The additional parts linked to the gate drive are used to add an offset voltage and small ramp to the current sense signal, as described in Section 8.2.2.8 in the UCC28070 datasheet (page 35).   Sometimes it is advantageous to add a small offset to CSA and CSB to improve the waveshape of the line current around the zero-crossing. 

For 3kW output at 230Vac input, expect a current of about 13.7Arms (higher if minimum input is lower than 230Vac).  13.7Arms = 19.4Apk, not including inductor ripple current.  
PE-63588NL is a 200:1 current-sense transformer (CT) rated for 600A-us when terminated with 200ohms.  This can be 1A for 600us, or 20A for 30us, or 600A for 1us.  
A more usual rating for CTs is a maximum volt-second value.  For PE-63588NL, 600A-us is equivalent to (600A/200)*200R = 600V-us. 

Assuming that you design for Vcsx = 3V at 19.4Apk x 110%, then 3V/(19.4/200) = 28.1 ohms.  A standard 1% value is 28.0 ohms.
It is important that the CT does not saturate, so considerable margin should be allowed to the 600V-us rating.  Sometimes magnetizing current can build up over several switching cycles.  For conservative design, limit each cycle to 100V-us.   Since the design is for 3V at the peak line current, each switching cycle can be at least 100V-us/3V = 33us long.
This is only on-time, but it indicates that switching frequency can be at least as as low as 1/33us = 30kHz (and even lower) so PE-63588NL should be adequate for this application.  

Regards,
Ulrich