In electronics , DC / DC switch mode power converter is a growing use . Portable applications, the main problem is the board space and thermal management, and therefore cost- efficient power conversion is critical to its terms . At present, the portable application designers decided to choose based on linear low- dropout regulators (LDO), sensing switch mode DC / DC converter, or capacitive charge pump DC / DC converter to meet its demand for power conversion , Faces in the overall cost, efficiency, integration, design flexibility and packaging and many other aspects of balance problems. Figure 1 Comparison of power conversion topology . The demand for power conversion Currently, many portable applications are using single lithium-ion battery , has all of the rechargeable batteries have the highest energy density and chemical properties , which can achieve the best small form factor design . The battery voltage is usually full to empty (full to empty) range of between 4.2V to 2.7V (from ), the battery voltage discharge cycle in the majority of about 3.7V. A wide range of applications of the technology in a non- rechargeable , single or dual cell alkaline battery system is also the acclaimed . Independent single- cell voltage range 1.5V to 0.9V. Many applications require multiple voltage rails to support the various components of the system . Common voltage rails are: 1.1V core voltage for the processor , memory, 2.5V and 3.3V, extended interface ( such as Compact Flash or USB interface) of 5V, and for LCD bias and white LED display backlight circuit system 28V. Made for various reasons should weigh the differences , we are here to provide several sets of power conversion options. Figure 1 shows a variety of DC / DC converter architecture overview. Existing solutions According to input and output voltage ratio , LDO ( low dropout ) regulator also apply to step-down applications . In short , LDO can occur any load resistance to change and adjust their internal resistance , so that a constant voltage regulator output . In short, the conversion efficiency is the output voltage and input voltage ratio of the decision . LDO voltage to 3.7V 3.3V memory rails can be generated in order to achieve up to 89% of the outstanding efficiency . However, the same battery 1.1V core voltage rail generated when it suddenly dropped to 29% efficiency . Currently , LDO uses such as chip-level and other ultra- small package size of only a few square millimeters , to achieve operating only ceramic input and output capacitor solution. Since LDO linear regulator solution, its almost non-existent output ripple , it is ideal for "noise -type "switch mode regulator , after the output filter , capable of supporting audio amplifier or RF circuitry . LDO output voltage differential with the input and current output increase increase , there would be moderate heat . Power loss is equivalent to input-output voltage difference is multiplied by the current through the linear adjustment of the product components . Charge pump (also called switched capacitor voltage converter ) or DC / DC converter , which uses a so-called "flying (flying) " or " pump (pump) " of the capacitor , inductor or transformer rather than to use energy Storage . It could not only increase or decrease the input voltage , but also for generating negative voltage . Internal FET switch array control , " flying " capacitor charge and discharge , according to its control, the input voltage multiplied or divided by 0.5,2 or three other factors , can produce the desired output voltage. Specific modulation scheme requires only ceramic capacitors can be up to 80% efficiency. As related to the switch, which will produce some output ripple charge pump will also generate EMI ( electromagnetic interference) . Some of the charge pump topology can be deployed dual charge pump structure , and the additional output voltage regulator in order to minimize EMI and ripple . The maximum charge pump output current limit of about 300mA or so , basically from the integrated switching transistor and the external " fly " by the decision of the size of the capacitor . Charge pump with space-saving SOT-23 package or no -lead quad flat package (QFN), can significantly reduce board space , and demands a more efficient LDO with space or budget, but not enough to implement more efficient induction DC / DC converter circumstances, to provide solutions. Figure 2 shows the display backlight applications, the core power for the white LED charge pump to provide application examples . Figure 2 SOT-23 package provides the core power for the white LED charge pump . Energy storage technology using electromagnetic induction switch mode DC / DC converter provides a difficult enterprise and the power conversion efficiency , whether it is higher or lower voltage, voltage under all circumstances, the case . Despite its relatively linear charge pump solution or solutions will require more than the board room , but this program is ideal for power conversion applications in higher current . Conversion to achieve minimum efficient cooling , and simplified thermal management , especially when compared with the LDO solution , especially when so often avoid the use of additional, bulky and expensive heat sinks needed. As can be up to 97% conversion efficiency , it will also help extend battery life. DC / DC converter as a DC / DC controller , when the designers have chosen a specific resistance of the external FET switch , and adjust based on the application the current needs of the current restrictions , which can provide the greatest design flexibility . At the same time , demands for tens of amps of current non- portable devices, it is particularly useful . Advanced packaging technology also allows the integration of switching transistor , so that switch mode DC / DC solution for the output current range SOT-23 package or chip-scale package, 100mA and TSSOP-28 package, any value between 9A . Taking into account the sensor with integrated FET switch mode DC / DC converter output current capabilities and efficiency , we can often achieve significantly improved space utilization efficiency solutions, often only one sensor, and the necessary input and output capacitors can be . Figure 3 shows the efficient use of DC / DC converter and linear regulator example. Step-up DC / DC converters can improve alkaline battery input voltage range between 1.5V to 0.9V , so the system can support 3.3V rail . Integrated on the same IC LDO can buck to support the processor core voltage of 1.8V . The two functions are integrated in 4mm x 4mm quad flat no- lead package (QFN) in order to minimize board space requirements . Figure 3, step-up DC / DC converter and by a single alkaline battery-powered LDO. Figure 4 shows the use of high energy efficiency and space-saving DC / DC buck converter example . Step-down DC / DC converters can be used to reduce the single lithium-ion battery input voltage , input voltage range between 2.7V to 4.2V , 1.2V processor core can support , 95% efficiency . The circuit also features the integrated switching FET, synchronous DC / DC buck converter , using only three external components , the space occupied by only the LDO circuit than most competing over 30% , it can provide nearly three times the Efficiency , and significantly extend battery life. Figure 4 , single Li-Ion applications, the voltage drop DC / DC converter