This paper presents a design and modeling of a block allowing converting a high voltage into a digital code which is used in a smart adaptive conditioning circuit to calibrate an electrostatic harvester for vibration energy. A smart energy management in the harvester is needed to achieve an optimal conversion of the vibration energy. This block is achieved with a successive approximation analogue-to-digital converter (SA ADC) and a voltage divider to reduce the voltage applied on the ADC. The design is done in Austrian Microsystem CMOS035HV technology. This study is validated by VHDL-AMS/ELDO modeling for the harvester, the divider and the harvester.