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A CMOS Current-mode DC-DC converter using a quadratic slope compensation scheme is presented. The use of a quadratic slope instead of a conventional linear slope makes a damping factor and a frequency bandwidth of a current feedback loop independent of the converter's output voltage. Further designing the coefficient of the quadratic slope to be fully dependent of the input voltage, the damping factor and the frequency bandwidth become completely independent of both the input and output voltages. A test chip of a buck converter in a 5 MHz operation which uses a quadratic slope compensation scheme has been fabricated by using a 0.35 mum CMOS process. The evaluation results show that with a current capability of up to 500 mA the frequency characteristics of the total loop are constant when the input and output voltages change from 3.3 V to 2.5 V and from 2.5 V down to 0.5 V, respectively, and also that the recovery time is 50 mus with a peak voltage deviation of less than 50 mV for load current changes from 20 mA to 200 mA and vice versa.
Date of Conference: 11-13 Sept. 2007