Analog and Interface Solutions Portable Power Conversion Design Guide www.microchip.com/analogDesign Guide Introduction and Contents Portable power conversion applications present unique and challenging design considerations. Innovative, small electronics require solutions with small footprints. In order to maintain battery life, portable applications require both high conversion efficiency and low standby power dissipation. Multi-cell battery packs may require step-down (buck) conversions and single cell batteries often require step-up (boost) conversions to maintain consistent power levels while the batteries discharge. Some products require constant voltage regulation for microcontrollers, sensors or RF signal processing while some circuits need constant current regulation for backlighting or battery charging. Microchip offers a broad array of solutions which feature small package sizes, high-efficiency, low standby power, accuracy and versatility solutions to solve these portable power conversion challenges. Table of Contents Step-Down (Buck) Switch Mode Power Converters ....................... 2 Linear (Low Drop Out) Regulators .................................. 9 Step-Up (Boost) Switch Mode Power Converters ....................... 12 Backlighting Solutions with Switching Regulators ...................... 17 Backlighting Solutions with Charge Pump DC/DC Converters .............. 19 Linear Battery Chargers ........................................ 20 Programmable Battery Chargers .................................. 22 Application Notes and Demonstration Boards ......................... 24 DC/DC Conversion Step-Down (Buck) Switch Mode Power Converters Step-Down (Buck) Switch Mode Power Converters For wide input range voltage sources and high output current applications switch-mode power converters offer a significant increase in efficiency compared to linear regulators. This results in longer battery run time in portable applications. Step-down or buck converters are used to regulate an output voltage that is always lower than the source voltage. Using inductors and capacitors for energy storage allows buck converters to commonly be more than 90% efficient, and under some circumstances they can be more than 95% efficient. Microchip offers a wide selection of buck converters and PWM controllers. Many of them are specifically designed to convert power from NiMH, Ni-Cd, Li-Ion, Alkaline multi-cell or 12/24V SLA batteries. Converters integrate power MOSFET switches used to commutate the supply current, while controllers rely on external power MOSFETs in diodes to switch the converter current. Synchronous converters rely on two MOSFETs working together to control the current flow, while asynchronous converters replace one MOSFET with a freewheeling power diode. Synchronous converters deliver higher efficiency for low output voltages, especially less than 3.3V, while asynchronous converters work well for higher output voltages. 2 Portable Power Conversion Design Guide