Charging Current Based on MAX1873

I am designing a kind of charging module which is base on MAX1873REEE.(This is the data-sheet of MAX1873REEE: )
My goal is to charge up the polymer battery–8.4V as well as the DC electrical source–12V. However,when in debugging, it’s OK if the current that DC electrical source provides is 1A. In another words, the Charging current is about 1.5A. But if the charging current is about 3A, there are some wrongs occurred here.In the beginning, the DC electrical source shows it’s 2A charging, but it will drop quickly and here just is 0.3A. Does anyone help me?

Thank you in advance.