Load-Independent Control of Switching DC-DC Converters With Freewheeling Current Feedback

A new control scheme of freewheeling current control is proposed for switching DC-DC converters. The output voltage is regulated by a comparator operation, and in the main current loop, the freewheeling current is feedback-controlled to a reference level in average. The converter control loop is no longer dependent on the values of the inductor, output capacitor, or the load equivalent resistance. The design of a loop compensator is therefore greatly simplified and the loop response can be very fast approaching that of a hysteresis converter. As an example, a single-inductor bipolar-output DC-DC converter with the proposed freewheeling current control is implemented in a 0.5 mum BiCMOS process. The converter has one positive output of 4 V and one negative output of -4.8 V. A maximum efficiency of 81% is achieved at a total output power of 250 mW with a switching frequency of 800 kHz.