Project Analog - February 2009 - (Page 6) to a different voltage potential in order to operate various integrated circuits (ICs) in the system. There are a variety of different converter topologies available, including linear regulators, switching regulators and charge pumps. Linear reguLaTors A linear regulator uses a voltagecontrolled current source to create a given output voltage. There are several different types of linear regulators, but for battery powered applications, the most common is the low dropout regulator (LDO), such as the MCP1703. This type of linear regulator uses a P-channel pass transistor as a variable resistor with feedback in order to regulate the output voltage. As this architecture relies on adjusting a resistive element to create a given output voltage, an LDO (or any linear regulator) can only create an output voltage that is lower than the input voltage. The minimum required differential voltage between the input and the output is called the dropout voltage. 6 · PRojeCt ANAlog · VolUme 3 / NUmBeR 1 Since an LDO uses only a single PNP transistor, it has a lower dropout voltage than the other linearregulator topologies. Another disadvantage of LDOs is they can be inefficient. The resistive element that is needed to drop the input voltage to the required level dissipates power in the form of heat. This is considered lost energy, as it is being supplied by the input source but is not being delivered to the output. This can also cause thermal issues as the regulator dissipates more and more energy in the form of heat. A system designer must be aware of the input and output voltage and current requirements. LDOs may not be a viable option for systems that require a large voltage drop and/ or a large output current due to the issues caused by self-heating. Despite these limitations, LDOs do provide some inherent advantages over other types of dc/dc converters. One advantage is that LDOs are relatively quiet in terms of noise, as there are no switching elements associated with their use. This can be very important to noise- Contents Viewpoint Selecting the Right dc/dc Converter Selecting the Right Battery System Understanding the Buck Switchmode Power Converter Analog news fig. 1 mcP1703 lDo Microchip analog page Sample center microchipDIRECT Reference designs/ app notes Technical training 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.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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