Project Analog - December 2007 - (Page 15) To enable this precision control the power controller needs to be able to sense many factors to generate the key values of peak available energy and total available energy. These key values definitions are as follows: Peak available energy can be defined as the amount of energy that can be sourced from the hybrid power source over a given short time, maybe a DVD startup or shutdown save to disk operation. The peak period will be based on the end equipment load profile. fig. 1 a PoWEr systEm using a hybrid PoWEr sourcE The battery-monitoring solution interfaces with the power controller via a data bus such as I2C, SMBus, or HDQ. This allows the power controller to have very accurate data on the state of charge (SOC) of the battery and to ensure safe use of the battery during charging and discharging. Monitoring the fuel cell and fuel cartridge is a little more challenging. The type and quantity of fuel available in the fuel cartridge, along with the present and average efficiency of the fuel cell, needs to be factored into the available energy from the fuel cell. In many instances, the fuel cartridge is unique to the system so the type of fuel can be stored in the power controller. In other solutions it may be beneficial to have the data for fuel stored with the fuel cartridge and provided to the power controller via a similar interface bus as the battery monitoring system. In solutions where the fuel cartridge has the capability to store data, it would be ideal to allow the power controller and possible refueling system to write back to the fuel cartridge the mea- Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news Total available energy can be defined as the total energy available from the hybrid power source, regardless of discharge rate. With this level of complexity, the system’s power path management must be precisely controlled to ensure the system load can always run to meet the end users demands on it. The most critical time is when the amount of available energy reaches a level where, under certain conditions, it can no longer power the system load and a limited-use configuration is initiated or even a controlled shutdown is performed. monItorIng the SyStem The battery can be monitored by a standard fuel gauge readily available in the market today such as the bq20z75 for two, three, or four series Li-ion cell configurations, or the bq27210 for single series Li-ion cell solutions. These solutions provide data based on voltage, current, temperature, and state-of-charge needed, as a minimum, by the power controller. cell and/or the battery can provide power to the system load. Also, when the dc supply is not present, the battery could also be charged by the fuel cell to maximize end-ofpower-shutdown capability or enable better dynamic power response to the system. When the dc supply is available, it provides energy to both charge the battery and power the system load. Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training 15 · 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
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