Project Analog - February 2009 - (Page 7) mcP73871 EvaluaTioN BoarD critical applications that involve sensitive measurements or systems that must pass strict governmental regulations. Other advantages of LDOs include ease of use and overall size. The most basic LDOs come in 3-pin packages, providing an input, output and a ground reference. Most LDOs require only a capacitor at the output for stability, providing for a very small system size. Finally, LDOs are typically more cost effective than the other dc/dc regulator architectures. swiTching reguLaTors In their most basic form, switching regulators use a diode, inductor and a switch in order to transfer energy from the input to provide a given output. Switching regulators can be configured in several different topologies including Buck, Boost and Buck/Boost. A Buck switching regulator provides a regulated output voltage that is lower than the input voltage, similar to the functionality of a LDO. A Boost switching regulator provides an output voltage that is higher than the input. This is a function that cannot be accomplished with a LDO. Finally, a Buck/Boost topology provides a regulated output across a range of input voltages that are above and/or below the output. The inductor inside the switching regulator acts as an energy-storage device and is much more efficient than the resistive element used in linear regulators. A switching regulator can achieve efficiencies of 85 percent or higher. Except in very specific conditions, an LDO cannot achieve this level of efficiency. Due to their high levels of efficiency, switching regulators are a better fit for higher-power applications, such as regulating a 24 V power bus down to 5V and supplying 500 mA to the load. In this case, a LDO would dissipate over 9W of energy in the form of heat, while only delivering 2.5 W to the load! For many portable applications, implementing a large heat sink or a cooling fan to account for thermal issues is not an option. As the name implies, switching regulators have a switching element, typically a transistor that is turned on and off rapidly. The frequency of this switching varies based upon the regulator’s design, and generates harmonics around the switching frequency. This switching noise can be problematic for circuitry that involves sensitive measurements, or for products that must past strict governmental regulations regarding electromagnetic interference. Integrated circuit manufacturers are making switching regulators easier and easier to use. However, most switching regulators still require the needed inductor to be external to the IC. The larger the inductor, the less effect the inductor current ripple will have on the regulated output. Hence, it is not practical to integrate the inductor in silicon. Depending upon the size of the inductor, this can be a considerable increase in the overall solution size. This external inductor can also create noise issues, so care must be taken when laying out the printed circuit board. Contents Viewpoint Selecting the Right dc/dc Converter Selecting the Right Battery System Understanding the Buck Switchmode Power Converter Analog news The MCP73871 Evaluation Board is designed to demonstrate Microchip’s stand-along linear Li-Ion battery charger with system power path and load sharing management control solution. The system load is also supported by the Li-Ion battery when input power is disconnected. A number of device options allow the MCP73871 device to be utilized in a variety of applications. Click here for more information on the MCP73871. Microchip analog page Sample center microchipDIRECT Reference designs/ app notes Technical training 7 · PRojeCt ANAlog · VolUme 3 / NUmBeR 1 http://www.microchip.com http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en536877 http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423
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