The problem about the parallel output of LTM4671

hi all:

Now I am using LTM4671 to generate three power supply for FPGA: 1.2V, 2.5V and 1.8V; the configuration of the LTM4671 is as follow:

VOUT0: 1.2V

VOUT3: 2.5V

VOUT1 and VOUT2: 1.8V

My circuit schematic is refer to Figure 31 of the datasheet.

1)Tie VOUT1 and VOUT2 together 

2)Tie VOSNS1+ and VOSNS2+ together and link to VOUT1 and VOUT2;

3)Tie FB1 and FB2 together, and use the 30.1K resistance downlink to GND;

4)Tie COMP1 and COMP2 together;

5)MODE/CLKIN12 float;

The VIN is +12V.

From the datasheet, if the RFB = 30.1K, the output = 0.6*(1+60.4/30.1)=1.8V, but now the actual output is 1.2V

If I change the RFB to 15.51K, the output will be 1.82V;

The outputs of VOUT0 and VOUT3 are OK..

Why?

Thanks!

Best wishes!