Current-Mode Converters with Adjustable-Slope Compensating Ramp

Sub-harmonic oscillation is a well-known problem in DC/DC converters with current mode control. To avoid this problem, a method to achieve adjustable-slope compensation is proposed. This method makes the compensating ramp slope appropriate for various output voltage levels. Besides solving the sub-harmonic oscillation problem, this method can also make the system respond better due to the alleviation of the over-compensation found in the traditional method, especially at low output voltage levels. Furthermore, power-saving in the current sensor is one other advantage because only the initial inductor current value in every cycle is needed. This can improve efficiency in current mode control, which is inherently lower than voltage mode control. An integrated circuit implementation of a current mode buck converter with the proposed method was made with a standard 0.35-mum CMOS process