Project Analog - December 2007 - (Page 13)

mcP1631 for intElligEnt PoWEr control systEms lar to air flow has a greater effect than does heat sink length. Therefore, a wider heat sink should be chosen over one with longer fin length. See Figure 4. mountIng the heat SInk Care should be taken to select a heat sink with a base plate close in size to the device it is used with. This ensures generated heat is evenly distributed over the surface of the heat sink. A size mismatch will increase the spreading resistance which can result in an increase in the heat sink’s thermal resistance by as much as 30%. fig. 4 heat sink orientation Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news The MCP1631 is a high-speed microcontroller based pulse width modulator (PWM) used to develop intelligent power systems. Alongside a microcontroller, the MCP1631 will control the power system duty cycle providing output voltage or current regulation. The microcontroller can be used to adjust output voltage or current, switching frequency and maximum duty cycle. The MCP1631 integrates a voltage and current sense amplifier. It also integrates a high-speed comparator used to protect the charger and battery from being exposed to high voltages if the battery is removed. click here for more information on the MCP1631. forced conVectIon cooLIng Providing forced convection with a fan or blower will significantly improve heat sink efficiency while at the same time facilitating the use of smaller, lower cost heat sinks. Heat sink fins should be vertically oriented to take full advantage of free air flow in natural (non-forced air) convection applications. Space should be provided to allow air to circulate to and from the heat sink. In addition, full advantage of radiation heat transfer should be taken by using a heat sink with an anodized or painted surface. Air flow should be parallel with the fins in forced convection cooled heat sink applications. A minimal amount of forced air will aid natural convection, so heat sink orientation with respect to the airstream should take priority. The width of the heat sink in the direction perpendicu- The thermal resistance between the device and the heat sink (ΘCS) depends on many variables such as type of interface material, interface material thickness, dry or grease filled joints, mounting force (clip load, screw torque), contact area, and surface flatness. Material or heat sink manufacturers will generally specify interface thermal resistances. Summary System thermal management considerations are not a trivial task. Many issues are involved in selecting the proper component, heat sink and airflow source. These issues need to be considered early in the design cycle to insure all options are available to implement the lowest cost, and most efficient thermal management solution. Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training • 13 · 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://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en531783 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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