Bidirectional current-mode capacitor multipliers for on-chip compensation

Abstract

Single-ended and two-ended bidirectional capacitor multipliers for providing on-chip compensation, soft-start, and fast transient mechanisms are proposed in this paper. The bidirectional current mode capacitor multiplier technique can effectively move the crossover frequency toward to the origin in the start-up period for a smoothly rising of the output voltage. Besides, the small time constant is set by the fast transient control circuit in order to get a higher crossover frequency. Thus, the output voltage can be regulated to its stable value as fast as it can when large load current changes. A test chip fabricated by the Taiwan Semiconductor Manufacturing Corporation (TSMC) 0.35-mu m process verifies the correctness of the bidirectional current mode capacitor multiplier technique. Experimental results demonstrate the transient speed by our proposed technique is faster than that by conventional. control by about 2 times, and there is only about 76% dropout voltage of the conventional design with off-chip compensation. The proposed circuits consume more quiescent current about 10 mu A in single-ended capacitor multiplier and 20 mu A in two-ended capacitor multiplier. With the proposed bidirectional current mode capacitor multiplier technique, the performance of dc-dc converters is improved significantly and the external pins and footprint area are minimized.