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A 0.9-V input discontinuous-conduction-mode (DCM) boost converter delivering 2.5-V and 100-mA output is presented. A novel low-voltage pulse-width modulator is proposed. The modulator can be directly powered from the 0.9-V input instead of using the 2.5-V output as in general modulator designs. Sophisticated low-voltage analog blocks, which normally consume a large amount of power and chip area, are not required in the modulator. The impact of output-voltage ripple and transient-induced output-voltage perturbation on the operation of analog blocks inside the modulator is eliminated. Boost converter start-up sequence is also greatly simplified. A CMOS-control rectifier (CCR) is also proposed to improve converter power efficiency. The CCR is used to replace the conventional rectifying switch to provide adaptive dead-time, which helps to minimize charge-sharing loss and body-diode conduction loss. Corresponding thermal stress on the rectifying switch is hence minimized. The CCR also enables the use of small off-chip inductor and capacitor at sub-MHz switching frequency to improve light-load efficiency. This converter has been implemented in a 0.35- mum CMOS process. It is designed to operate at ~ 667 kHz with a 1 mu H inductor and 4.7 mu F output capacitor to reduce both switching loss and form factor. Experimental results prove that the converter can be directly powered from 0.9-V input with ~ 85% efficiency at 100-mA output.
Date of Publication: Sept. 2008