I have found theta-ja=58.5C/W in ADP2303 datasheet.
But what is theta-jc value?? because I can't find it in datasheet.
Is there particular reason why customer cannot use the theta-JA and looks for theta-JC? If customer insists, please course request through a local FAE because this will take time to run simulation.
I found a reference table in attached file that you can use as starting point for computation estimate. You should go to Plastic SO, S8.