I have observed in LT spice that at soft start pin there is around 23V..but on my PCB am getting 2.4V..Can anyone knows about it??
That is caused because you haven't changed the
Spice analysis command to "start external supplies at 0 volts".
I have one more theory then I think you must take the measurements Ron S. has asked for.
Here is the theory: The .01 ohm sense resistor is very small. The traces on your PCB could easily be .05 ohms. So check this:
The resistor going to the sense pin should be connected at the top of the .01 ohm resistor. When I say at the top I mean right to it not an inch or cm away.
The other end of the .01 ohm resistor should have a
big short trace (or wire) directly to the ground of the IC.