The slew rate of the inductor current is limited by the inductance value and the voltage across the inductor. In a buck converter, when the controller is saturated, the voltage across the inductor during a step-up load transient is V in − V ou t , while during a step-down load transient, it is −V ou t . Thus, a buck converter with a large conversion ratio offers asymmetrical step-up and step-down transients. Since the rate of fall of the inductor current is much slower than the rate of rise of the inductor current, the step-down transient lasts longer than the step-up transient for the same change in the load current. The step-down slew rate can be increased by reducing the inductance, but it results in higher inductor current ripple, and hence, higher losses in the power converters. In this paper, we present a novel topology for improving the step-down load transients without reducing the inductance value. The scheme operates only during load transients and restores to the normal operating conditions during steady-state operation. It provides reduced voltage overshoots and faster settling times in output voltage during such transients. The proposed scheme is tested on a 1-V/12-A buck converter switching at 1 MHz, and the experimental results are presented.Index Terms-Current-mode control, high slew rates, voltage regulator module (VRM).
Current sensing is one of the important function in a DC-DC Converter. It may be used for implementing current mode control or for achieving current sharing in a paralleled converters. Many current sensing schemes have been reported in literature, but they are either lossy or they require precise knowledge of the component value. In this paper a new Giant Magneto Resistive (GMR) effect based sensor is used for low voltage, high current VRM type applications. Since the current sensing is based on magnetic field, thus the sensing accuracy depends upon the placement of sensor on the conductor. Various implementation issues while using such a sensor are studied and finally the performance of the sensor is studied on a 1V/15A buck converter switching at 1MHz.
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