Project Analog - December 2007 - (Page 9)

fig. 1 thE incrEasing numbEr of smartPhonE fEaturEs is driving thE nEEd for morE loWvoltagE outPut rails at varying PoWEr lEvEls. at the smartphone block diagram in Figure 1, it is easy to see how the increasing number of features is also driving the need for more lowvoltage output rails at varying power levels. the uSe of a hdd A key driver for the adoption of a HDD inside a PMP or smartphone has been the need for large and easily read/writeable compact storage. Consider the case of the PMP. It can usually be powered from an ac adapter, a USB cable, or the Liion battery; although managing the power-path control between these power sources presents a significant technical challenge. Another common dc/dc converter problem is to generate a regulated output voltage that lies somewhere between a wide range of input voltages. To help put this problem into a clearer perspective, it is useful to consider a single-cell Li-ion battery PMP with a 3.3 V power rail. A conventional lithium-cobalt oxide cathode cell has a discharge profile from a high of 4.2 V down to 3.0 V. Nevertheless, the system power rail requires a fixed 3.3-V output. As can be seen, the output voltage is at times above, below, and equal to the input voltage range for the Li-ion battery. The traditional approach taken to solving this type of problem has been to use either a single-ended primary inductance converter (SEPIC) or a buck/boost converter. These types of converters will deliver a fixed output voltage whether the input voltage is above, below, or equal to the output voltage. However, SEPIC converters present some significant drawbacks: * Complicated design due to the multiple inductors or bulky transformer required. The control loop is complex and difficult to stabilize under a wide input voltage range typical with Li-ion battery applications. The solution footprint is large and also has a high height profile. The efficiency of conversion is low: usually mid 70% to low 80%. Thermal problems can arise at higher-output power levels. Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news At the same time, memory and I/O voltage requirements can vary between 2.5 and 3.3 V. Thus, it is becoming impractical to use multiple point-of-load (POL) dc/dc converters directly from the Li-ion battery, and so system designers are adopting a more integrated approach. Similarly, cellular phones do more than just allow people to talk with each other. Most “smart” cellular phones allow Web browsing, wireless transfer of e-mail, photography, streaming video, TV reception, and even GPS capability. 9 · prOject AnALOg · Dec 07 An embryonic trend is to also include a micro hard-disk drive for high-capacity storage capability. There are 10-Gbyte microdrives on a single platter only 1-in. in diameter that are already proven and available, with 0.8-in.-diameter platters on the near-term horizon. The 1-in. disk drives need only about 300 mA at 3.3 V for normal operation; although during spin-up, peak current demand can reach 500 mA. Future 0.8-in. models will need less nominal current and will have peak currents less than 400 mA. Looking * Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training * * * 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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