Techniques for high-performance integrated switched-mode DC-DC converters

Power management ICs are essential in all electronic systems nowadays for providing regulated supply voltages to internal functional blocks from the rude and unregulated power sources such as batteries, household line power and energy harvesters. Switched-mode DC-DC converters are one of the most crucial integrated DC-DC converters, as they can provide the highest power efficiency and offer the flexibility to perform both step-up and step-down voltage conversions. Current-mode switching DC-DC converters are widely used in all battery-operated portable electronic devices such as cell phones, digital cameras, PDAs, etc. Minimizing the required inductance and the inductor size in the power stage of the converter is important for reducing the cost and the board area of the power module. The switcher thus needs to be operated at a high frequency that depends on both the speed of the current sensor and the control scheme of the converter. This thesis develops a speed- and accuracy-enhanced current sensor for sensing the inductor current and an auto-selectable peak- and valley-current control scheme for relaxing the settling time requirement of the current sensing. As a result, a current-mode switcher can operate at a high switching frequency of 5 MHz, use a small-value off-chip inductor of 1 muH, and achieve the peak power efficiency of 91%.;In addition, switched-mode DC-DC converters are also necessary for power conditioning in a rapid-growing area of energy harvesting. Long battery run time and small physical size are important requirements for energy-harvesting-assisted electronics (EHAE), so it is crucial for the switcher to achieve high power efficiency over a wide load range and be area efficient simultaneously. This thesis proposes a single-inductor triple-input triple-output (SITITO) DC-DC converter for the EHAE application, as the SITITO converter offers the most area-efficient and low-cost solution. Only a single inductor is used in the proposed SITITO converter while the converter extracts energy from two independent energy harvesters and provides two regulated output voltages and one regulated current for battery charging without the cross regulation. For minimizing power losses of SITITO converter over a wide range of load currents, a multi-mode control scheme that regulates each output of the converter by using either the pulse-width modulation (PWM) or the switching-timing-aware pulse frequency modulation (STAPFM) is developed. Together with the sub-threshold operation of the proposed multi-mode controller, the proposed SITITO converter is able to achieve a peak power efficiency of > 87% for the load range between 0.3 mW and 42 mW. The capability of extracting energy from two independent energy harvesters via timing interleaving in the proposed SITITO converter can further extend the battery run time of EHAE.