This paper reports a new functional design and modeling of a vibration energy harvester composed from a mechanical resonator (MEMS), capacitive transducer and a conditioning circuit based on the BUCK DC- DC converter architecture. The basic configuration of conditioning circuit from [1][2] is enhanced with two major features for the power management allowing, firstly, to adapt dynamically to the variation of external vibration parameters and, secondly, a smart interface with the load, witch allows the system to manage a possibly variable load and to adapt to different situations (e.g. insufficient generated power level, load too large, etc.). The study is validated by behavioral VHDL-AMS/ELDO modeling.