This paper introduces a new current-programmed controller for non-inverting buck-boost converters. The controller facilitates tight voltage regulation and excellent transient convergence, all carried out through a simple CPM controller hardware. Steady-state operation for the full range of conversion ratios is supported with seamless transitions between modes and improved efficiency and ripple characteristics around unity conversion gain. In case of a load transient, an optimized boundary control scheme achieves near-optimal recovery, with programmable constrains for the voltage deviation and inductor current, covering the entire range of conversion ratios. The operation of the controller is experimentally verified on a 2-15V input to 3.3V output, non-inverting buck-boost converter, demonstrating significant improvement in steady-state around unity gain as well as fast convergence for load transients with programmable constraints for the output voltage deviation and inductor current.