Project Analog - December 2007 - (Page 17)

Managing the SOC is a major departure from how a battery is used in most portable applications today. Typically the battery is the only wireless power source, so it has to provide all the power to the host system. Therefore, it needs to store as much energy as it safely can. This provides the ultimate goal of the longest run time. Also, battery charging time is important—the shorter the better! sure also that the system load has enough power from the dc supply when it is connected by regulating the battery charging current. The recent smart battery data set (SBDS) addendum adding fuel cell data to the existing data set that supports batteries, allows the host to access data that enables it to control the use of the fuel cell and the battery. The use of the power controller can handle the complexity of the HPS and enable the SBDS fuel cell additions to assist the host system to use the HPS more effectively. The simple addition of total available energy from the fuel cell and battery can provide a basic level of functionality to the host system to indicate available run time, remaining time alarm (RTA), or remaining capacity/ energy alarm (RCA). An equation for predicting runtime is as follows: AtRateTimeToEmpty (ARTTE) = Total Available Energy / AtRate( ) This equation allows the host system to determine the available run time based on what the host system knows about what the user is trying to do, for example, play a DVD, or run a system diagnostic. It is only beneficial if the host system has information about the energy it uses in different modes and for different programs. controLLed ShutdoWn and maxImIzed hpS run tIme Predicting runtime for the user is a “crystal ball” approach as the future is hard to predict. However, the data provided can be used for enabling a controlled system shutdown when power is low. The more accurate the function is, the longer the system run time. The measurement error must be added to controlled shutdown reserve to ensure that under all conditions the system will perform a controlled shutdown. The improved accuracy of measuring total available energy is directly added to the user available energy. Hence, longer run time can be achieved with exactly the same potential energy source, as shown in Figure 2. Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news integrating a fuel cell with a battery, supercapacitor, or other power storage device as a combined power source solves several dynamic power supply and thermal issues. Tradeoffs can be made with charge time, peak SOC, and longevity of the battery. But these are not common in today’s consumer applications. These two usage dynamics don’t apply when it comes to the HPS, so a better balance between the optimal states of the battery and fuel cell can be achieved by using the power controller. Ideally, the battery in a HPS will last for the lifetime of the HPS without needing to be replaced. To achieve this goal the power controller can enable battery charge management options such as charging at lower voltages, charging at slower rates, and temperature compensation of the charge voltage/ rate. The power controller can en- Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training • 17 · 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://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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