UCC28070A: Interleaved 4 Phase operation using UCC28070

Hello Venkatesh,

There are not many changes needed to adapt the UCC28070 to 4-phase operation. 
The biggest change (in my opinion) is that a pair of synchronized SYNC pulses are required to achieve the 4-phase interleaving at 90-degree phase shift between them. 
See Figure 6-1 on page 20 of the UCC28070A datasheet.  
The SYNC pulses are themselves at 180 degrees and each IC then splits its SYNC input into a local 180 degrees, with the net result that all 4 phases are shifted by 90 degrees between them. 

The Excel design tool does not directly accommodate calculations for 4-phase interleaving, but it can be used to design 2-phase interleaving at 1/2 of the total output power.
Obtain all of the component values based on the 1/2 of your total Pout target. 
Then, you simply have two 2-phase power stages - each processing 1/2 of the total power - connected and operating in parallel. 

A few exceptions to being connected in parallel can be seen in Figure 6-1:
a) VREF1 and VREF2 must not be connected together.
b) RT1 and RT2, and DMAX1 and DMAX2, must not be connected together.
c) The four CAOx outputs must not be connected together.
d) RSYNTH1 and RSYNTH2 must not be connected together.
e) CDR1 and CDR2 are connected to their respective VREFs, not connected together.
f) RDM1 and RDM2 are used to receive the separate SYNC signals.

g) VSENSE, VINAC, and PKLMT can have common divider networks; they don't have to have their values paralleled.
h) Cout1 and Cout2 can be paralleled into a single Cout of double value. 
i)  Css1 and Css2 can be paralleled into a single Css of double value. 
j) Rimo1 and Rimo2 can be paralleled into a single Rimo of 1/2 value.
k) VAO compensation components Cpv, Czv, and Rzv values can be combined at double the capacitances and 1/2 the resistance. 

If you wish to simply double your 3.3kW design into a 6.6kW design, most of your work is already complete.
Follow the connection advice listed in points a) through k) above. 
The values for RTx and DMAXx, must be adjusted up about 10% to accommodate the requirements for External Clock Synchronization.
See Section 6.3.4 in the UCC28070A datasheet, page 18, for important details on "sync'ing". 
I recommend to minimize the pulse widths of the SYNC pulses. 

Regards,
Ulrich