Project Analog - December 2007 - (Page 7)

mcP73833/4 output VoLtage reguLatIon accuracy The output voltage regulation accuracy is critical in order to obtain the desired goal: maximize battery capacity usage. A small decrease in output voltage accuracy results in a large decrease in capacity. However, the output voltage can not be set arbitrarily high because of safety and reliability concerns. Figure 1 depicts the importance of output voltage regulation accuracy. charge termInatIon method It can not be stressed enough that over charging is the Achilles’ heal of Li-Ion cells. Accurate charge termination methods are essential for a safe, reliable, charging system. ceLL temperature monItorIng The temperature range over which a Li-Ion battery should be charged is 0°C to 45°C, typically. Charging the battery at temperatures outside of this range may cause the battery to become hot. During a charge cycle, the pressure inside the battery in- Battery dIScharge current or reVerSe Leakage current In many applications, the charging system remains connected to the battery in the absence of input power. The charging system should minimize the current drain from the battery when input power is not present. The maximum current drain should be below a few microamperes and, typically, should be below one microampere. concLuSIon Properly restoring energy using the latest battery technology for today’s portable products requires careful consideration. An understanding of the charging characteristics of the battery and the application’s requirements is essential in order to design an appropriate and reliable battery charging system. The guidelines and considerations presented in this article should be taken into consideration when developing any battery charging system. Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news The MCP73833/4 is designed to operate alongside a host microcontroller or in stand-alone applications. It adheres to all the specifications governing the USB power bus, for applications charging from a USB port. • Complete Linear Charge Management Controller • Constant Current / Constant Voltage Operation with Thermal Regulation • High Accuracy Preset Voltage Regulation: 4.2V, 4.35V, 4.4V, or 4.5V, + 0.75% • Programmable Charge Current: 1A Maximum • Preconditioning of Deeply Depleted Cells • Automatic End-of-Charge Control • Automatic Recharge • Two Charge Status Outputs • Cell Temperature Monitor • Low-Dropout Linear Regulator Mode • Automatic Power-Down when Input Power Removed • Available Packages: 3mm x 3mm DFN-10 and MSOP-10 click here for more information on the MCP73833/4 creases causing the battery to swell. Temperature and pressure are directly related. As the temperature rises, the pressure can become excessive. This can lead to a mechanical breakdown inside the battery or venting. Charging the battery outside of this temperature range may also harm the performance of the battery or reduce the battery’s life expectance. Generally, thermistors are included in Lithium-Ion battery packs in order to accurately measure the battery temperature. The charger measures the resistance value of the thermistor between the thermistor terminal and the negative terminal. Charging is inhibited when the resistance, and therefore the temperature, is outside the specified operating range. Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training • 7 · prOject AnALOg · Dec 07 http://www.microchip.com http://www.microchip.com/analog http://www.microchip.com/analog http://www.microchip.com/batterychargers http://www.microchip.com/batterychargers http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://ww1.microchip.com/downloads/en/DeviceDoc/22005a.pdf 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

Table of Contents Feed for the Digital Edition of Project Analog - December 2007

Project Analog - December 2007 Contents Viewpoint About Project Analog Sponsor4 Charging Lithium-Ion Batteries: System Considerations New Trends In Battery-Powered Portable Devices Low Power Design: LDO Thermal Considerations Runtime Measurements for a Hybrid Power Source Battery-Powered System Design Considerations Analog News—Analog News from Multiple Sources Enter to Win an iPhone Contact Project Analog Sponsor Mindi™ Battery & Power Circuit Simulator Microchip Advanced Parts Selector (MAPS)

Project Analog - December 2007

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