Method and device for charging a storage device with energy from an energy harvester

A power management integrated circuit (1) for charging a storage device with energy from an energy harvester comprising

• an input terminal (11) for receiving an input power (Pin) from the energy harvester,
• a voltage converter (20) for converting said input power (Pin) into an output power (Pout) and wherein said voltage converter (20) comprises
• i) a main voltage converter (22) operable if an output voltage Vout_VC at an output node (24) of the voltage converter (20) is equal or larger than a first voltage value V1, and
• ii) a coldstart voltage convertor (21) operable if said output voltage Vout_VC is lower than said first voltage value V1,
• a first input/output terminal (12) connectable with a storage device (50),
• a first conductive path (5) conductively coupling said output node (24) of the voltage converter (20) with said first input/output terminal (12), and wherein said first conductive path (5) comprises a switching device (41) configured for opening and closing said first conductive path (5), and
• a second input/output terminal (13) connectable with a buffer capacitor (30), and wherein said second input/output terminal (13) is conductively coupled with said output node (24) of the voltage converter (20) such that a voltage Vbf of the buffer capacitor when being connected to said second input/output terminal (13) corresponds to said output voltage Vout_VC, characterized in that said coldstart voltage converter (21) when operable is configured for transferring charges from said input terminal (11) to said second input/output terminal (13) until the voltage Vout_VC has reached said voltage value V1, and in that said power management integrated circuit (1) comprises
• a second conductive path (6) conductively coupling said output node (24) of the voltage converter (20) with said first input/output terminal (12), and wherein said second conductive path (6) comprises a current control device (42) configured for opening and closing said second conductive path (6) and configured for limiting a current flow in said second conductive path (6) to a maximum value when said second conductive path (6) is closed, and
• a controller (40) configured for
• i) disabling operation of the coldstart voltage converter (21) and enabling operation of the main voltage converter (22) if said output voltage Vout_VC has reached said voltage value V1,
• ii) controlling said current control device (42),
• iii) monitoring said voltage Vout_VC at said output node (24) of the voltage converter (20),
• iv) monitoring a parameter Msto indicative of a voltage Vst at the first input/output terminal (12),
• v) if Msto is lower than a reference value Msto-min then maintaining the first conductive path (5) open and repetitively performing steps of
• a) controlling a charge transfer from said input terminal (11) to said second input/output terminal (13) by monitoring an increase of the voltage Vout_VC and if Vout_VC reaches a second voltage value V2, with V2>V1, then closing the second conductive path (6), and
• b) controlling a charge transfer from said second input/output terminal (13) to said first input/output terminal (12) by monitoring a decrease of the voltage Vout_VC and if Vout_VC reaches a third voltage value V3, with V1<V3<V2, then opening the second conductive path (6),
• vi) closing the first conductive path (5) if Msto is equal or larger than said reference value Msto-min,
• and wherein said reference value Msto-min is indicative of a reference voltage value Vst-ref of said storage device, with V1<Vst-ref<V3.