What suppliesthe ae2100d3 fadec with power until engine rpm is sufficient for the alternator stator to take control?

The FADEC already has power prior to engine start. In fact it controls the entire start sequence. It receives power under normal starting conditions via an ECBU ; the acft will have power from either an external source, the APU, or an operating engine. The alternator stator provides power to the FADEC once the engine reaches 10% NG. This way the engine is entirely self sustaining once started and during the majority of start sequence. Should the alternator stators fail, power is then given from the ECBU again (28v DC power source).