Multibit Σ-Δ PWM digital controller IC for DC-DC converters operating at switching frequencies beyond 10 MHz

An integrated digital controller for dc-dc switch-mode power supplies (SMPS) used in portable applications is introduced. The controller has very low power consumption, fast dynamic response, and can operate at programmable constant switching frequencies exceeding 10 MHz. To achieve these characteristics, three novel functional blocks, a digital pulse-width modulator based on second-order sigma-delta concept (Sigma-Delta DPWM), dual-clocking mode compensator, and nonlinear analog-to-digital converter are combined. In steady state, to minimize power consumption, the controller is clocked at a frequency lower than SMPS switching frequency. During transients the clock rate is increased to the switching frequency improving transient response. The controller integrated circuit (IC) is fabricated in a standard 0.18-mu m process and tested with a 750-mW buck converter prototype. Experimental results show the controller current consumption of 55 mu A/MHz and verify closed-loop operation at programmable switching frequencies up to 12.3 MHz. Simulation results indicating that this architecture can potentially support operation at switching frequencies beyond 100 MHz are also presented.