Project Analog - December 2007 - (Page 10)

fig. 2 a morE simPlifiEd building block aPProach is a good altErnativE to suPPlying a hdd With thE nEcEssary PoWEr during thE natural dischargE cyclE of this nEWEr tyPE of li-ion battEry. is 4.2 V down to 2.5 V, this would leave more than 30% of the battery’s energy unused. In this instance, a more-simplified building-block approach is a good alternative to supplying a HDD with the necessary power during the natural discharge cycle of this newer type of Li-ion battery. In this case, a monolithic synchronous buck-boost converter that can deliver a fixed 3.3-V output regardless of whether the input voltage was above, equal to, or below the output voltage would be the ideal solution. Many devices in the market today address this need, such as the LTC3532 buck-boost converter from Linear Technology (see Figure 2). In a single-cell Li-ion battery-powered PMP, a 1-in. miniature HDD needs a constant 3.3 V at a nominal 300 mA, with 500-mA peak currents. The output voltage from the Sony’s Nexelion battery varies from 4.2 V down to as low as 2.5 V. The LTC3532 would operate in step-down mode while the battery voltage declines from 4.2 V to a nominal 3.3 V. At 3.3 V, the LTC3532 will operate in four-switch buck-boost mode. This four-switch operation ensures a smooth switchover between buck and boost modes, providing no jitter, ripple, or erratic noise generation. Once the battery voltage drops below 3.3 V and continues down to 2.5 V, the LTC3532 operates in stepup mode. In addition to the above, there is also a growing demand for a moderately integrated switching dc/dc converter that can supply multiple outputs with high-efficiency operation at moderate current levels. Such a converter would easily find a home in either a PMP or smartphone. Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news A more effective approach would be to use a single inductor-based converter that can control four internal switches to perform the stepdown, step-up, and 100% duty cycle modes. This part would have the advantage of being easy to design, having high power density, and providing high-efficiency operation because of its synchronous drive capability. SuppLyIng 3.3 V, 500 ma for hdd SpIn-up It is clear that designers of PMPs have several options available to ensure that battery life is optimized 10 · prOject AnALOg · Dec 07 for their particular configuration. A combination of multifunction ASSPs can provide the necessary voltages and power levels to provide optimum system performance while ensuring that the power drain on the battery is minimized during normal operation. However, an ASSP might not be able to use the complete energy density of the newer cathode chemistry Liion batteries such as Sony’s Nexelion product family. The reason is that once the battery’s voltage is below the required 3.3-V output level, the ASSP cannot boost this battery voltage to the required output level. Since the Nexelion battery range • 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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