This paper introduces a lock-in integrated controller for resonant SCC. The controller identifies the resonant period of each sub-circuit on-the-fly and locks-in to the correct switching time to fully utilize the charge transfer rate for each flying capacitor. The various modules of the controller are detailed, including the auto-tuner and sequencer which accommodate any mismatch, variations or drifts of component values or circuit configuration. The IC has been designed and fabricated on a 0.18μm 5V process resulting in effective silicon area of 0.64mm2. Post-layout results of the controller IC operating in closed-loop are provided, demonstrating accurate lock-in for two resonators with individual independent resonant characteristics. A full-scale hardware prototype of 650W 4:1 switched-tank-converter is used to validate the controller's operation prior to IC fabrication, demonstrating excellent lock-in capabilities resulting in high efficiency of up to 98.6%.