In today's highly information-based society, portable smart devices are helping everyone all the time. At the same time, many of them need corresponding power management modules to provide them with stable power from the Li-ion battery. Since different functional modules require different voltage levels, a special DC-DC converter or driver must be designed to meet the requirements. In this thesis, one design is proposed to fulfill the requirement of high efficiency, and another one achieves fully integrated. This thesis proposes a hybrid DC-DC step-up converter with a new architecture by merging a traditional inductor-based (IB) boost converter with a switched-capacitor (SC) converter to boost 3-4.2-V input to 20-30-V output. By serially connecting an IB boost converter and a 1:6 Dickson SC converter, the capacitors take over most of the output voltage stress. As a result, the voltage stress over each switch is limited to 5 V, which makes it possible to implement all the power switches with only on-chip 5-V devices. Thanks to the 5-V devices, the overall power conversion efficiency is improved in various aspects. The switching frequency of the SC stage is decreased by the soft charging technique, which helps further improve the efficiency. The proposed converter is designed and simulated in TSMC 0.18 um BCD process. An efficiency of 93.08 % is achieved under 3.7-V input and 29-V output voltage with a 25-mA current load. A fully integrated VCSEL driver with adjustable pulse width is also proposed in this thesis. By combining two separate control signals, the VCSEL driver is able to overcome challenges posed by PVT and technology process limitations to achieve the narrowest pulse width of around 300-ps. The proposed converter is designed and simulated in SMIC 55 BCD process.