An implantable medical device (IMD) includes multiple stimulation engines for independently stimulating respective electrode sets of a lead system while avoiding collisions and/or channel contention during stimulation delivery. A first voltage multiplier is configured to generate an adjustable target voltage having sufficient headroom at an output node that is commonly coupled to anodic nodes of respective stimulation engines. Each stimulation engine includes a secondary voltage multiplier to drive the respective anode and a current regulator powered by a floating voltage supply, wherein the current regulator is coupled to a cathodic node and configured to control how much stimulation current is pulled from the patient tissue.