As mentioned, you can't regulate both current and voltage at the exact same time. However, you can still have two control loops; one voltage and one current. The way you set it up is to have one dominate the other. Usually the current loop dominates by putting an upper limit on current flow. For example, in a lead acid battery charger, the current control loop will limit the current until the voltage rises to the charge termination voltage. Then the voltage control loop kicks in and maintains a steady voltage as the current decreases due to the battery being unable to absorb any more charge. Once the current drops to a certain level, then the voltage loop set point is updated to a lower voltage to maintain the battery charge level (float voltage) as the battery is fully charged. What I just described is called a 3 stage charger.