A Power Management Circuit for a portable electronic device comprising an internal battery to be charged either through a first interface or through an AC_DC conversion circuit. The circuit comprises a first buck/boost converter having a Switched Mode Power Supply (SMPS) mode which can be controlled either in a buck or a boost mode, said first buck/boost controller being associated with a first external coil for the purpose of embodying a battery charging circuit through a first interface (USB). The circuit further comprises a second buck/boost converter which can also be controlled either in a buck or a boost mode. Bypass circuits are used for performing, under control of a control circuit, the bypass of either the voltage of the battery or the voltage generated by said buck/boost controllers when in boost mode to a second interface (SIM/MMC).