This work desribes a configurable converter together with a constant current stimulator. 600 pF on-chip MIM flying capacitors are utilized to provide 3.3/6/9/12 V output with load current ranging from 100 to 900 uA. The converter changes its output, i.e., stimulator supply voltage depending on the digitally controlled stimulation current. This eliminates the unused voltage headroom and provides more efficient operation compared to constant voltage converters. In-vitro tests show a decrease of up to 79% in the power dissipation of the constant current stimulator compared to its constant 12 V operation.