The maximum discharge current you can pull from the PMID output depends on if adapter (VIN) is present or not. Operating on BAT only mode, the max current from PMID will be your Current Limit on Discharge Mode (IBAT_OCP). When the adapter is present the max current from PMID will be your Input Current Limit (ILIM) + IBAT_OCP. You can find the currents specs of the BQ25120A on the Electrical Characteristics table of the datasheet.